Plant Toxins: What You Need to Know
Plants are often described as healthy foods, and many people are encouraged to eat more vegetables, fruit, grains, nuts and legumes. However, there is another side to the subject that receives less attention in everyday dietary advice: plants also produce chemicals that can defend them against insects, animals, fungi and other threats.
Some of these chemicals can be harmful to humans. Depending on the compound, the amount consumed and how the food is prepared, the effects can range from mild digestive discomfort to severe poisoning. Research has also raised questions about whether certain plant compounds can influence processes in the body over longer periods.
Some people argue that plant defence chemicals may contribute to chronic disease and that removing plant foods from the diet can improve health. These arguments raise legitimate questions about plant chemistry and human nutrition. However, some of the broader conclusions go beyond what current research has established.
This page examines why plants produce defensive chemicals, what scientific research says about specific examples, how these substances may affect the human body, and what remains uncertain about their long-term effects.
Medicinal Uses of Plants and the Difference Between Medicine and Food
Plants have been used for medicinal purposes throughout human history. Long before modern pharmaceutical research, people relied on traditional knowledge of herbs, roots, leaves, bark and other plant materials to address a wide range of ailments. This knowledge developed across different cultures and traditional medical systems, and some of it later provided important starting points for scientific research into plant compounds. [17, 18]
The contribution of plants to modern medicine is significant. Some medicines used today originated from substances found in plants, while others were developed through the investigation of traditional medicinal practices. Examples include aspirin, whose development was influenced by the traditional use of willow bark; artemisinin, developed from sweet wormwood and used to treat malaria; and the cancer medicines vinblastine and vincristine, derived from the Madagascar periwinkle. These examples demonstrate that plants can contain biologically active substances with important medicinal applications. [18]
There are, however, different considerations when examining plants as sources of medicine and plants as foods. A substance may have a useful therapeutic effect under specific conditions without making the whole plant suitable for regular consumption. Medicinal preparations may use particular plant parts, extracts or isolated compounds, rather than the whole plant in the form in which it would normally be eaten. The composition, concentration and intended use of a medicinal preparation can also differ considerably from ordinary dietary exposure. [19]
There is an important distinction between using compounds derived from plants medicinally and regularly consuming plant foods such as vegetables, fruit, grains, legumes, nuts, seeds and herbs as part of our diet.
Medicinal use: Certain plants contain biologically active substances that can be used to treat specific conditions. Some modern medicines were developed from compounds first identified in plants.
Traditional medicine: Long before modern pharmaceutical research, traditional healers used plants and plant preparations to address a wide range of ailments. Some traditional uses subsequently led to the discovery of medically useful compounds.
Dietary consumption: A compound that has a therapeutic effect at a particular dose does not automatically make the whole plant beneficial or harmless when eaten regularly. Its effects depend on the substance, dose, preparation, route of exposure and individual circumstances. [19, 20]
Plants can therefore be considered from two very different perspectives: as sources of medicinal substances and as foods that form part of our regular diet. Their medicinal applications are one aspect of their chemistry. Their natural chemical defence compounds, and the potential effects of those compounds on the human body, are another. Both deserve to be examined in their own right.
Plant Toxins, Individual Tolerance and Vegetarian or Vegan Diets
Plants contain naturally occurring chemical defence compounds. Some of these compounds can affect digestion, nutrient absorption and other biological processes. However, people do not all respond to plant foods in the same way.
Some people follow vegetarian or vegan diets and thrive on them, including athletes who achieve exceptional levels of physical performance. Their experiences demonstrate that a diet containing a wide variety of plant foods can work very well for some individuals.
This does not mean that plant foods are free from chemical defence compounds or that everyone tolerates them equally well. Equally, the presence of these compounds does not mean that everyone who eats plant foods will experience adverse effects.
Why do some people thrive on vegetarian or vegan diets while others experience unwanted effects from vegetables and other plant foods? Research indicates that individual responses can be influenced by several factors, including digestive function, specific food intolerances, underlying health conditions and differences in how the body processes dietary compounds. The gut microbiome may also contribute, although its precise role in individual tolerance is not yet fully understood. The available research does not establish one explanation that accounts for everyone's response to plant foods.
Understanding these differences is important when considering plant foods, their naturally occurring compounds and individual dietary tolerance.
1. Why do plants produce toxins?
Plants are living organisms. Unlike most animals, they cannot run away from predators or physically fight off an animal trying to eat them. Over millions of years, plants have therefore developed a range of ways to survive, reproduce and protect themselves.
One of these strategies is the production of chemical compounds that can discourage feeding, interfere with digestion, damage cells or make a plant less attractive to potential predators. Plants also produce chemicals that defend against fungi, bacteria and other organisms.
Scientists call many of these substances secondary metabolites. This term refers to compounds that are not directly required for basic processes such as producing energy or building the plant's main structural components, but that can provide other advantages, including defence.
Examples include alkaloids, lectins, tannins, glucosinolates, cyanogenic glycosides and various other compounds. Their functions and effects differ considerably. Some are harmful to particular insects but have little effect on humans at ordinary dietary exposure. Others can be dangerous to humans if consumed in sufficient quantities.
The World Health Organization recognises that naturally occurring toxins can be produced by plants as defence mechanisms against predators, insects and microorganisms. It also identifies natural toxins as a genuine food-safety concern because some can cause serious illness. [1]
Plant defence is not limited to chemicals. Plants may also have thorns, tough outer layers, irritating hairs or other physical barriers. Chemical defence is simply one part of a much wider range of survival strategies.
Plant Defences and Toxins: What Do They Mean for Human Health?
Plants produce natural chemicals to protect themselves from insects, animals and other threats. Some of these chemicals are also present in the vegetables we eat and can affect the human body.
The effects vary depending on the compound, the amount consumed, how often it is eaten and how the food is prepared. Individual tolerance also matters. People can differ in their sensitivity to particular compounds and in how their bodies digest, process and respond to them. A vegetable that causes symptoms in one person may be tolerated by another without noticeable problems.
The presence of a plant defence chemical does not automatically mean that a vegetable is harmful. Equally, being a commonly eaten food does not mean that every compound it contains is harmless. Understanding the potential effects requires looking at the specific compounds, the amounts people consume and the available evidence about their effects on human health.
2. What did research into natural plant chemicals reveal?
One of the scientific papers frequently discussed in connection with plant toxins is a 1990 study by Bruce Ames, Margie Profet and Lois Gold, titled Dietary Pesticides (99.99% All Natural). Ames was a biochemist known for his work on mutagenicity and chemical carcinogenicity. [2]
The paper examined the chemicals that plants naturally produce to defend themselves, as well as the way scientists assess potential cancer risks from chemicals in food.
The authors estimated that approximately 99.99% by weight of the pesticide chemicals in the American diet were naturally occurring substances produced by plants. They also reported that, of 52 natural pesticides that had been tested in high-dose animal cancer tests, 27 produced cancer in rodents.
These findings are often cited to illustrate that plants contain many naturally occurring chemicals with biological activity, including some that can cause cancer in experimental animals.
The research makes an important point: chemicals produced by nature should not automatically be assumed to be harmless simply because they are natural.
However, the paper also has an important limitation that is sometimes overlooked. A substance causing cancer in a high-dose animal experiment does not establish that eating the food containing it causes cancer in humans at ordinary dietary exposure.
The dose, the substance's potency, the way it is absorbed and processed, and the amount people actually consume all matter.
Ames and his colleagues were examining how to assess chemical risks, including the need to consider actual exposure rather than simply count chemicals that have produced a positive result in animal tests. Their paper does not demonstrate that ordinary consumption of vegetables causes cancer or that avoiding all plant foods reduces cancer risk. [2, 3]
The distinction is between identifying a potential hazard and demonstrating a meaningful risk under real-world conditions.
This research supports the conclusion that natural plant chemicals deserve scientific investigation. It does not, by itself, establish that plants as a food category are harmful to humans.
3. What are the main types of plant toxins?
There are many different plant compounds, and they do not all behave in the same way. Some can interfere with digestion or nutrient absorption, some can irritate tissues, and others can be acutely poisonous.
The following sections examine several compounds discussed in debates about plant defence chemicals and in food-safety research.
Lectins
Lectins are proteins found in many plants, including beans, lentils, peas, grains and certain vegetables. Their defining characteristic is that they bind to particular carbohydrate structures.
Plants produce lectins for various biological functions, including defence. Some lectins can bind to cells lining the digestive tract, and particular types can cause harmful effects when consumed in an active form.
One well-known example is phytohaemagglutinin, a lectin found in kidney beans. Raw or inadequately cooked kidney beans can contain enough active lectin to cause severe nausea, vomiting, abdominal pain and diarrhoea.
The European Food Safety Authority (EFSA) published a scientific assessment of the risks of plant lectins in food in 2026. It concluded that inadequately prepared foods containing active lectins, particularly legumes, can cause adverse effects. It also found that appropriate preparation, including soaking and thorough boiling of beans, effectively deactivates the relevant lectins. [5]
This is an established example of a plant defence compound causing harm to humans.
However, lectins are a diverse group of proteins. Findings about one lectin cannot automatically be applied to every lectin in every plant food.
Some arguments about lectins go further, suggesting that lectins in foods such as wheat and legumes may interact with the intestinal lining, affect receptors and contribute to inflammation or disease.
There is scientific research examining these mechanisms, but the strength of evidence varies. Laboratory and animal studies can show that particular lectins have biological effects. They do not automatically establish that eating ordinary amounts of properly prepared foods causes the same effects in humans over many years.
The EFSA assessment found that the available human evidence was limited, with important gaps in the quality and design of studies. It did not establish a direct causal relationship between dietary lectins and autoimmune disease. [5]
It is therefore reasonable to recognise that lectins can be harmful in certain circumstances without concluding that all lectin-containing foods are harmful.
Phytates and phytic acid
Phytic acid is a compound found in foods such as seeds, nuts, grains and legumes. Plants use it to store phosphorus, particularly in seeds.
Phytic acid can bind minerals such as iron, zinc and calcium in the digestive tract. This can reduce the amount of those minerals available for absorption from a meal.
For this reason, phytic acid is often described as an antinutrient. The term refers to a substance that can interfere with the absorption or use of certain nutrients.
The practical effect depends on the overall diet, the amount consumed, the mineral involved and the body's nutritional status. A single meal containing phytic acid does not necessarily lead to a nutritional deficiency.
Food preparation can also affect phytate levels. Soaking, germination, fermentation and certain cooking processes can reduce the amount or influence of phytate in some foods.
The relevant question is whether the overall diet supplies sufficient absorbable nutrients. The presence of phytate is a real biochemical fact, but the amount by which it affects nutritional status depends on the wider dietary context.
Oxalates
Oxalates are compounds found in a variety of plant foods, including spinach, rhubarb, certain nuts and some other vegetables.
Oxalate can bind to calcium and contribute to the formation of calcium oxalate crystals. These crystals are the most common type of kidney stone.
A review published in the American Journal of Physiology—Renal Physiology examined the relationship between dietary oxalate and kidney stone formation. It described evidence linking urinary oxalate levels to the risk of calcium oxalate stones. Dietary oxalate contributes to urinary oxalate, although the body also produces oxalate itself. [6]
This is an example of a plant-derived compound with a clinically relevant effect in at least some circumstances.
However, the risk is not identical for everyone. Hydration, kidney function, calcium intake, intestinal absorption and other individual factors can influence the likelihood of stone formation.
People with a history of calcium oxalate kidney stones or certain medical conditions may need specific dietary advice. It does not follow that everyone who eats oxalate-containing foods will develop kidney stones or that all such foods must be avoided.
Tannins
Tannins are compounds found in foods such as tea, certain fruits, nuts, legumes and grains. They can bind to proteins and other substances, which is partly responsible for the bitter or astringent taste of some foods.
Tannins can affect the activity of digestive enzymes and the absorption of certain nutrients under particular conditions. Their effects depend on the type of tannin, its concentration and the food in which it occurs.
The fact that tannins can interact with proteins or minerals does not automatically mean that ordinary dietary exposure causes clinically significant harm.
Claims about tannins need to be assessed compound by compound and in relation to actual consumption, rather than treating all tannins as one uniform toxin.
Cyanogenic glycosides
Cyanogenic glycosides are plant compounds that can release hydrogen cyanide under certain conditions. They occur in several plant species, including cassava, some varieties of almonds and the kernels of certain stone fruits.
Cyanide interferes with the body's ability to use oxygen at the cellular level. A sufficiently high exposure can be life-threatening.
Cassava is an important example. It is a major food source in several parts of the world, but some varieties contain substantial amounts of cyanogenic compounds and require appropriate processing before consumption.
The World Health Organization explains that cyanogenic glycosides occur in at least 2,000 plant species, including several that are used as food. The risk depends on the amount of cyanide released and the exposure a person receives. [1]
Acute cyanide poisoning can cause symptoms such as dizziness, headache, vomiting, breathing difficulties, confusion, convulsions and, in severe cases, death.
Long-term exposure to inadequately processed cassava has also been associated with serious health problems in populations that depend heavily on it, particularly under conditions where exposure is high and nutritional circumstances are poor. [1]
This is clear evidence that certain plant compounds can cause both acute and longer-term harm. It is not evidence that all plants are dangerous or that the risk from properly prepared cassava is equivalent to the risk from inadequately processed cassava.
Glycoalkaloids in potatoes
Potatoes and other plants in the nightshade family produce glycoalkaloids. In potatoes, the best-known examples are alpha-solanine and alpha-chaconine.
These compounds help defend the plant against pests and other threats. Concentrations can be higher in green, sprouting or damaged potatoes, particularly around the sprouts and eyes.
EFSA has assessed the potential health risks of glycoalkaloids in potatoes. High exposure can cause gastrointestinal symptoms such as nausea, vomiting and diarrhoea. Peeling and some cooking methods can reduce the amount present, although the reduction varies. [7]
Food-safety authorities therefore advise consumers to avoid potatoes that are very green, heavily sprouted or bitter.
This is a practical example of why the condition of a food and the way it is handled matter. It is not evidence that an ordinary potato prepared and stored appropriately carries the same risk as a potato with elevated glycoalkaloid levels.
Glucosinolates and other plant compounds
Some vegetables, particularly those in the cabbage family, contain glucosinolates. When plant tissue is damaged, enzymes can convert these compounds into other substances, including isothiocyanates.
These compounds are part of the plant's defence system. They are also being studied for their biological effects in humans.
The effects of such compounds can be complex. A substance may be toxic to certain organisms or harmful at a high dose while having different effects at the levels normally encountered in food.
It is therefore not sufficient to identify a plant compound as biologically active and then assume that it necessarily causes harm in humans.
The same principle applies to other plant chemicals. Each compound needs to be assessed according to its biological effects, dose, exposure and evidence from human studies.
4. Tea: Plant Compounds and Their Effects on Humans
Tea is a plant-derived drink made by infusing leaves in water. Black, green, white and oolong tea all come from the plant Camellia sinensis. Herbal infusions, such as peppermint or chamomile, are made from other plants and have different chemical compositions.
Tea contains several plant compounds, including caffeine, tannins and other polyphenols. It can also contain minerals absorbed by the plant from the soil, including fluoride. The amounts vary according to the type of tea, growing conditions, processing and preparation.
The fact that tea contains plant compounds does not by itself establish that drinking tea is harmful. The effects need to be considered separately, based on the compound involved and the evidence from human studies.
Caffeine in tea and its effects
Caffeine is a stimulant that affects the central nervous system. Its short-term effects in humans are well established. It can increase alertness and reduce the perception of tiredness, but it can also cause restlessness, anxiety, palpitations and difficulty sleeping, particularly at higher doses or in people who are sensitive to it.
The European Food Safety Authority has assessed caffeine safety. For healthy adults, it concluded that single doses of up to 200 mg and total daily intake of up to 400 mg generally do not raise safety concerns. For pregnant and breastfeeding women, the assessment recommends keeping total daily caffeine intake to no more than 200 mg. These amounts include caffeine from all sources, not just tea. They are safety guidance, not targets that everyone needs to reach. People can experience unwanted effects at lower amounts. [10]
Tea usually contains less caffeine per serving than many coffees, but the amount depends on the tea, the quantity used and the brewing method. Drinking several cups can contribute a meaningful amount of caffeine to a person's daily intake.
For someone who experiences anxiety, palpitations or disturbed sleep, reducing caffeine or avoiding it later in the day may help. These are recognised effects of caffeine, rather than evidence that all the other compounds in tea are harmful.
Tannins and other polyphenols
Tea contains polyphenols, including compounds commonly described as tannins. These contribute to tea's flavour and astringency.
Some tea polyphenols can reduce the absorption of non-haem iron when tea is consumed with a meal. Non-haem iron is the form found in plant foods and in some fortified foods, whereas meat contains haem iron as well as non-haem iron.
The effect on iron absorption depends on the meal and the individual's circumstances. For most people, the presence of polyphenols in tea does not by itself demonstrate that drinking tea will cause iron deficiency. However, people with low iron levels or a higher risk of iron deficiency may be advised to avoid drinking tea with meals to reduce its effect on iron absorption.
Tea polyphenols are also studied for their biological activity. Laboratory findings and observational studies have prompted interest in possible health effects, but such findings do not prove that drinking tea prevents disease or that the polyphenols are beneficial for every person.
It is important to distinguish between a compound having an effect in an experiment and evidence that drinking a beverage produces a meaningful health outcome in humans.
Fluoride in tea
Tea plants can absorb fluoride from the soil. The amount in a cup of tea can vary depending on the plant, the growing conditions, the type of tea and how it is prepared.
Fluoride is not automatically harmful simply because it is present in a drink. The relevant issue is total exposure from all sources and the amount consumed over time.
Excessive fluoride exposure during tooth development can cause dental fluorosis. Much higher long-term exposure can cause skeletal fluorosis, which affects bones and joints. These conditions are associated with excessive exposure, not merely the detection of fluoride in a food or drink. The US National Institutes of Health Office of Dietary Supplements describes the sources, nutritional role and potential effects of fluoride. [11]
The amount of fluoride obtained from tea varies considerably. The fact that some teas contain fluoride does not, by itself, establish that ordinary tea consumption produces harmful exposure. Equally, it is not possible to assess exposure accurately without considering the tea consumed and other sources of fluoride.
Does drinking very hot tea increase cancer risk?
The International Agency for Research on Cancer (IARC) classified drinking very hot beverages, generally defined as beverages consumed above 65°C, as probably carcinogenic to humans. The concern relates to repeated thermal injury from very hot drinks and the observed association with oesophageal cancer. It is not a finding that tea itself is a carcinogen. The same temperature-related concern can apply to other beverages consumed at similarly high temperatures. [12]
This distinction matters. The issue identified by IARC is the temperature at which a drink is consumed, rather than a specific plant toxin in tea.
Allowing tea to cool before drinking reduces exposure to very high temperatures. The classification does not mean that tea consumed at a comfortable drinking temperature has been shown to cause oesophageal cancer.
What does the evidence establish about tea?
Human research establishes that caffeine can affect alertness, sleep and anxiety, and that tea can influence the absorption of non-haem iron when consumed with meals. Excessive fluoride exposure can also cause recognised health problems, although the fluoride content of tea varies and the presence of fluoride alone does not establish harmful exposure. Drinking beverages at very high temperatures is a separate concern.
By contrast, many broader claims about tea's long-term benefits or harms rely on observational research, laboratory findings or proposed mechanisms. Observational studies can identify associations, but they cannot by themselves establish that tea caused an outcome. People who drink tea may differ from those who do not in other ways that influence their health.
The available evidence therefore does not support a simple conclusion that tea is either universally beneficial or inherently harmful because it contains plant compounds. Its effects depend on factors such as caffeine intake, individual sensitivity, iron status, total fluoride exposure and drinking temperature.
Tea and a carnivore diet
A strict carnivore diet excludes tea because tea is derived from a plant. Some people following more flexible versions of a carnivore diet choose to drink tea, while others avoid it.
Whether tea fits a person's dietary approach is a separate question from whether ordinary tea consumption has been shown to cause harm. The presence of plant compounds is a reason to examine the evidence, but it does not prove that drinking tea is harmful to everyone.
At Healing by Nutrition, we distinguish between what a plant contains, what has been demonstrated to affect humans and what someone chooses to include or exclude from their diet.
5. Coffee: Plant Compounds and Their Effects on Humans
Coffee is made from the roasted seeds of coffee plants. Like tea, it contains caffeine and a range of other naturally occurring compounds. These include chlorogenic acids and other polyphenols, as well as substances formed or changed during roasting.
Coffee is often discussed in terms of its possible health benefits, but it is also a source of compounds that can have physiological effects or raise food-safety questions. The relevant evidence differs from one compound to another.
The presence of a chemical in coffee does not automatically mean that drinking coffee is harmful. Equally, claims about possible benefits should not be treated as proof that coffee prevents disease.
Caffeine and its effects
Caffeine is one of the best-studied active compounds in coffee. It can increase alertness and temporarily reduce tiredness, but it can also cause anxiety, restlessness, palpitations and sleep disturbance. The effects depend on the dose, timing, individual sensitivity and other sources of caffeine in the diet.
EFSA's caffeine assessment concluded that single doses of up to 200 mg and total daily intake of up to 400 mg generally do not raise safety concerns for healthy adults. For pregnant and breastfeeding women, the assessment recommends no more than 200 mg of caffeine per day from all sources. These are general safety guidance levels, not amounts that everyone needs or should aim to consume. Some people experience unwanted effects at considerably lower doses. [10]
The amount of caffeine in coffee varies according to the type of coffee, the serving size, the preparation method and the beans used. A large serving can contain substantially more caffeine than a small cup.
For people who experience poor sleep, anxiety or palpitations, reducing coffee intake or changing the timing of consumption may help. These effects are directly related to caffeine and do not establish that every other compound in coffee is harmful.
Cafestol and kahweol: compounds that can raise cholesterol
Coffee contains naturally occurring compounds called diterpenes, including cafestol and kahweol. Their amounts in the finished drink depend heavily on how the coffee is prepared.
Cafestol can raise blood cholesterol, particularly LDL cholesterol. Research comparing coffee preparation methods has found that unfiltered coffee, such as coffee prepared in a French press or boiled directly, can raise cholesterol more than filtered coffee. Paper filters retain much of the cafestol, reducing the amount that reaches the cup.
A randomised study comparing filtered coffee with cafetière coffee found that the preparation method affected blood cholesterol. The research was supported by the Netherlands Heart Foundation through the Netherlands Organisation for Scientific Research, rather than by the coffee industry. [13]
This is a useful example of why the preparation method matters. Two cups of coffee can differ in their exposure to particular compounds even when both are made from coffee beans.
The evidence does not mean that every type of coffee has the same effect on cholesterol. Nor does it mean that all coffee drinkers will experience the same change. The diterpene content, amount consumed and individual response all matter.
Acrylamide: a compound formed during roasting
Acrylamide can form when certain foods are cooked at high temperatures. It is found in a range of foods, including coffee, because it can develop during the roasting process.
Acrylamide has raised food-safety concerns because it has produced cancer-related effects in some animal experiments. However, assessing the risk to humans from the amounts encountered in food is more complicated. The dose received, how the body processes the compound and the relevance of experimental exposures all matter.
The US National Cancer Institute summarises the evidence concerning acrylamide in food and cancer. Human studies have not established a consistent relationship between dietary acrylamide exposure and most cancers. This does not prove that acrylamide is harmless at every exposure level, but it means that the presence of acrylamide in coffee is not, by itself, proof that drinking coffee causes cancer. [14]
Acrylamide is not unique to coffee, and its presence should not be treated as evidence that coffee is necessarily harmful as a whole. The relevant question is whether typical human exposure produces a measurable health risk.
Furan and related compounds
Furan and some related compounds can form during the heating or processing of food. Coffee is one of the foods in which they can be found, partly because roasting involves high temperatures.
EFSA has assessed furan and methylfurans in food. Toxicological research has raised concerns about potential liver effects and cancer risk, particularly from animal studies. However, translating those findings into a precise estimate of risk for humans consuming ordinary amounts of coffee is difficult. Exposure from the overall diet and the amount consumed both matter. [15]
The presence of furan in coffee therefore warrants assessment, but it does not establish that drinking coffee causes liver disease or cancer in humans. The evidence needs to distinguish between a hazard observed in experimental studies and the actual risk at realistic levels of exposure.
Does coffee prevent disease?
Research on coffee has reported associations between coffee consumption and various health outcomes. Some observational studies have found that people who drink coffee have lower rates of certain diseases, while other findings vary by outcome and population.
These associations should not be interpreted automatically as proof that coffee prevents disease. People who drink coffee may differ from people who do not in smoking habits, diet, physical activity, health status and other factors. Statistical adjustments can account for some differences but cannot remove all possible confounding.
Laboratory studies also examine coffee compounds for possible biological effects. Such findings can help identify mechanisms for further investigation, but they do not establish that drinking coffee produces the same effects in the human body or improves long-term health.
It is therefore not justified to treat coffee as a medicine or to assume that everyone should drink it for health reasons. Equally, observational associations and the presence of compounds such as acrylamide do not establish that ordinary coffee consumption is necessarily harmful.
What does the evidence establish about coffee?
Human evidence establishes that caffeine can affect alertness, sleep and anxiety. There is also evidence that coffee preparation influences the amount of cafestol consumed and that unfiltered coffee can raise blood cholesterol more than paper-filtered coffee. [10, 13]
Coffee also contains acrylamide and furan, which have raised toxicological concerns. However, the presence of these compounds does not by itself establish that ordinary coffee consumption causes cancer or liver disease in humans. The assessment of actual risk requires evidence about human exposure and health outcomes. [14, 15]
Many claims about coffee's long-term benefits rely on observational research. Such research can identify associations but cannot, by itself, establish that coffee caused the apparent benefit.
Coffee's effects therefore depend on the amount consumed, caffeine sensitivity, preparation method and individual circumstances. It is not scientifically accurate to label coffee either a universal health-promoting drink or a proven cause of chronic disease based solely on its chemical composition.
Coffee and a carnivore diet
Coffee is derived from a plant and is excluded from a strict animal-only carnivore diet. Some people following flexible versions of the diet continue to drink coffee, while others choose to avoid it.
The decision to include coffee in a particular dietary approach is separate from the question of whether it has been shown to cause harm. The evidence supports specific conclusions about caffeine and the cholesterol-raising effects of diterpenes in unfiltered coffee, but it does not establish that all coffee consumption is harmful to everyone.
At Healing by Nutrition, we distinguish between the presence of a plant compound, a demonstrated effect in humans and a personal decision about what to include in a diet.
6. Can plant compounds interfere with nutrient absorption?
Yes. Certain plant compounds can reduce the absorption of particular nutrients under some conditions.
Phytate can bind minerals, oxalate can bind calcium, and some tannins can affect the availability of nutrients. Certain lectins can interfere with the normal functioning of the digestive tract when they remain active in food. [5, 6]
This is why the term antinutrient is used in nutrition research.
However, three separate questions need to be considered.
First, does a compound reduce the absorption of a nutrient? In some cases, the answer is yes.
Second, does that reduction result in a meaningful nutritional problem? That depends on the quantity consumed, the overall diet, the individual's nutritional requirements and other factors affecting absorption.
Third, does the effect cause long-term disease or shorten lifespan? That requires additional evidence and cannot be inferred simply from the first finding.
A food can contain a substance that reduces the absorption of one nutrient while supplying other nutrients. The overall effect must be assessed in the context of the entire diet.
Some arguments about plant compounds emphasise that nutrients listed in food-composition tables are not necessarily all available to the body. The underlying point that the amount of a nutrient in a food is not always identical to the amount absorbed is correct. However, the degree of absorption varies, and it is not accurate to assume that nutrients from plant foods are generally unavailable or that animal foods are entirely free from factors affecting nutrient absorption.
The scientific question is how much of each nutrient is absorbed and whether the person's diet supplies enough to meet their needs.
7. Do plant toxins damage the gut lining?
The intestinal lining is a barrier between the contents of the digestive tract and the internal environment of the body. It allows nutrients to be absorbed while helping to prevent unwanted substances and microorganisms from crossing into the circulation.
Certain lectins can interact with cells lining the intestine. Research, including experimental work, has examined whether some lectins can affect intestinal cells, alter barrier function or influence the gut microbiome.
The EFSA assessment of plant lectins reviewed evidence relating to intestinal effects. It found that particular lectins can cause changes in intestinal structure and function in experimental animals, while also identifying substantial limitations in the available human evidence. [5]
This is a legitimate area of scientific investigation.
However, the phrase leaky gut is often used broadly in online discussions to suggest that ordinary plant consumption routinely damages the intestinal barrier and allows toxins to enter the body. That broad claim is not established by the evidence reviewed here.
Intestinal barrier function can be affected by various conditions, including infections, inflammatory diseases and other factors. Demonstrating that a purified lectin affects intestinal cells in an experiment does not establish that eating a particular food causes chronic intestinal damage in a healthy person.
To establish that claim, researchers would need well-designed human studies showing that realistic dietary exposure produces the proposed effect and that the effect leads to meaningful health consequences.
8. Do lectins cause inflammation, autoimmune disease or Parkinson's disease?
Some arguments about plant defence chemicals suggest that certain compounds may contribute to inflammation and autoimmune conditions. Others propose that lectins could be involved in the development of Parkinson's disease.
These claims require careful examination because they involve several steps between a chemical's biological activity and the development of a human disease.
Lectins and autoimmune disease
Autoimmune diseases occur when the immune system attacks the body's own tissues. Their development can involve genetic susceptibility, environmental influences and other biological factors.
One proposed mechanism is that certain foreign substances may resemble structures in the body closely enough to influence immune responses. This is sometimes discussed in relation to molecular mimicry.
Although molecular mimicry is a recognised biological concept, showing that it can occur does not prove that dietary lectins are a general cause of autoimmune disease.
The EFSA assessment concluded that a direct causal relationship between dietary lectins and autoimmunity remains to be demonstrated. [5]
Some people report that particular foods worsen their symptoms, and food-related conditions such as coeliac disease are well established. But a person's reaction to one food does not demonstrate that all plant foods cause autoimmune disease or that removing every plant food is necessary for everyone with an autoimmune condition.
Lectins and Parkinson's disease
Parkinson's disease is a neurological condition involving the loss or dysfunction of particular nerve cells. Researchers have investigated whether, in at least some cases, processes associated with the disease may begin in the gastrointestinal tract and involve pathways connecting the gut and brain.
Research has examined vagotomy, a surgical procedure in which part or all of the vagus nerve is cut. The vagus nerve connects the brain with organs including the digestive system.
A Danish study published in 2015 examined whether people who had undergone vagotomy subsequently had a different risk of Parkinson's disease. The study explored the hypothesis that a disease-related process might travel from the gut towards the brain along the vagus nerve. It did not test whether plant lectins cause Parkinson's disease. [8]
A later Swedish study found no statistically significant association between vagotomy overall and Parkinson's disease, although it reported a possible lower risk in a subgroup of patients who had undergone truncal vagotomy. The authors described the findings as suggestive rather than conclusive. [9]
These studies are relevant to research on the possible relationship between the gut and Parkinson's disease. They do not demonstrate that dietary lectins travel along the vagus nerve and cause the disease.
That is a separate hypothesis requiring direct evidence.
It is important to distinguish a proposed mechanism from a demonstrated cause. A study showing a possible relationship between a surgical procedure and disease risk cannot automatically be used to establish that a particular food compound causes that disease.
9. Do plant chemicals cause cancer?
Some naturally occurring plant compounds have produced cancer in laboratory animals, particularly when tested at high doses. The Ames, Profet and Gold paper is one of the studies frequently cited in this discussion. [2]
However, cancer risk depends on more than whether a substance can produce a positive result in an animal experiment.
The dose, the compound's potency, the duration of exposure, the way the body processes it and the relevance of the experimental conditions to humans all matter.
The same distinction applies to claims about vegetables containing numerous known carcinogens. A list of chemicals that have produced carcinogenic effects in particular experimental settings does not tell us the overall effect of eating the food in which those chemicals occur.
It is also necessary to distinguish between different types of natural toxins. For example, certain pyrrolizidine alkaloids can damage DNA and are a recognised food-safety concern. These compounds may contaminate foods through particular plants entering the food supply. The World Health Organization identifies the potential cancer risk from certain pyrrolizidine alkaloids, while noting that exposure and overall risk require assessment. [1]
This demonstrates that natural toxins can present genuine long-term health risks. It does not establish that the wide range of compounds present in ordinary plant foods collectively causes cancer in people who consume those foods.
The scientifically relevant question is not simply whether a compound can cause cancer at some dose. It is whether actual human exposure creates a meaningful risk.
10. Can small amounts of plant toxins cause harm over decades?
This is one of the most important questions in the wider debate.
Some harmful effects occur after a single high exposure. Others can arise from repeated exposure over time. The outcome depends on the chemical involved.
A compound may be rapidly broken down and eliminated from the body. Another may produce repeated tissue damage if exposure continues. Some compounds or their metabolites can accumulate under particular circumstances, while others do not accumulate in the same way.
It is therefore not scientifically accurate to treat all plant toxins as if they behave identically.
The World Health Organization notes that natural toxins can produce both acute and chronic effects. Depending on the substance, long-term consequences may involve the nervous, immune or reproductive systems, or cancer. [1]
However, the existence of chronic toxicity from certain compounds does not establish that ordinary consumption of all plant foods causes cumulative damage.
To assess long-term risk, researchers need to know which compound is involved, how much people consume, how much is absorbed, how it is processed by the body and what health outcomes occur over time.
A compound that causes harm at a high dose may present little risk at a much lower exposure. Conversely, some compounds can pose a concern at relatively low exposures if their toxicity and the duration of exposure warrant it.
The word toxin alone does not provide enough information to determine the risk.
Does the body accumulate all these chemicals?
No general conclusion can be made about all plant compounds. Their absorption, metabolism and elimination differ.
Some substances may be broken down rapidly. Others may remain active during digestion, and some can produce adverse effects through repeated exposure.
For example, the concern with inadequately cooked kidney beans is primarily acute poisoning from active lectins. The concern with cyanogenic compounds in inadequately processed cassava can include both acute and longer-term effects. The risk from glycoalkaloids in potatoes depends partly on the concentration in the potatoes consumed. [1, 5, 7]
These examples illustrate why each substance needs to be assessed separately.
The further claim that small amounts of a broad range of plant chemicals accumulate over decades and inevitably damage the human body has not been established.
11. Does cooking make plant foods safe?
Cooking and other forms of food preparation can reduce the risk from some plant toxins, but the effect depends on the compound.
For example, soaking and thoroughly boiling kidney beans effectively deactivate the lectins responsible for acute poisoning. Peeling and some cooking methods can reduce glycoalkaloids in potatoes, although they do not necessarily remove them completely. Cassava requires appropriate processing to reduce cyanogenic compounds. [1, 5, 7]
Other compounds may be more resistant to heat or may require different methods of preparation.
This is why food-safety recommendations are specific to the food and the hazard involved.
The fact that a toxin can be reduced through preparation does not mean that every plant compound is eliminated by cooking. Equally, the fact that a compound remains in some amount after cooking does not establish that the remaining amount causes harm.
The relevant issue is the level of exposure and the evidence concerning the effects of that exposure.
12. Are humans naturally adapted to eating plants?
Humans are biologically capable of digesting and absorbing nutrients from a range of foods, including animal and plant foods. However, the ability to eat a food does not mean every amount or preparation method is safe.
Throughout human history, populations have eaten different combinations of animal foods, plants and other available foods. Their diets have varied according to geography, climate, culture and food availability.
Some people argue that humans are better suited to a meat-based diet and that avoiding plant defence chemicals may help explain the improvements some people report on a carnivore diet.
This is an interpretation of human biology and nutrition. The existence of plant toxins alone cannot establish the ideal diet for the human species.
To answer that question, research would need to consider nutritional requirements, digestion, metabolism, health outcomes and the long-term effects of different dietary patterns.
A food's evolutionary history may provide useful context, but it does not replace evidence about its effects on human health.
13. Does a carnivore diet eliminate plant toxins?
A strict carnivore diet excludes plant foods and therefore eliminates dietary exposure to the plant compounds found in those foods. That is a clear difference between a carnivore diet and a diet containing plants.
However, eliminating exposure to a compound does not automatically mean that doing so improves health. The benefit depends on whether the compound was causing a problem at the exposure level involved.
Some people report substantial improvements in symptoms after removing plant foods. Such experiences may be important to the individuals concerned and can help identify questions for further research.
However, individual experiences cannot establish which part of the dietary change caused the improvement. Other changes may include reductions in carbohydrate intake, changes in total energy intake, the removal of particular foods, changes in weight or alterations to other lifestyle habits.
A strict carnivore diet also removes many foods that provide nutrients and other compounds. Its long-term effects therefore need to be assessed as a whole rather than by considering only the plant substances it removes.
The evidence discussed on this page establishes that certain plant toxins can be harmful under particular conditions. It does not establish that eliminating all plant foods is necessary for good health or that a carnivore diet is universally superior to other dietary approaches.
14. Tolerance to Plant Toxins
People do not necessarily respond to plant compounds in the same way. Differences in digestion, metabolism, individual sensitivity and the amount and type of food consumed may influence how someone responds to particular compounds.
Some people appear to tolerate a wide variety of plant foods without noticeable problems. Others report symptoms associated with certain foods, even when those foods are commonly regarded as healthy. Some may tolerate one plant food but experience problems with another.
Tolerance is therefore an important part of the discussion. The fact that one person can eat a particular food without apparent difficulty does not establish that everyone will respond in the same way. Equally, an individual's symptoms do not prove that a particular plant compound is responsible.
The term plant toxins also covers different substances with different properties. Not every defensive compound has the same effects, and the presence of a compound does not automatically mean that eating the plant will cause harm. The amount consumed, how the food is prepared and the individual's response can all matter.
This helps explain why the discussion cannot be reduced to the simple claim that plants are either safe or harmful for everyone. Individual tolerance deserves consideration alongside the biological properties of the compounds themselves.
15. What Happens When People Remove Plant Foods from Their Diet?
Understanding plant defence compounds is one part of the discussion. Another is the experience of people who report that their health improves after they stop eating plants. These experiences deserve consideration because they concern what people actually notice when they change their diets, rather than only what laboratory research tells us about individual compounds.
People who describe improvements after adopting a carnivore diet have reported changes involving a wide range of health problems. These include digestive difficulties, irritable bowel symptoms, inflammatory and autoimmune conditions, skin problems, joint and back pain, fatigue, allergies, neurological symptoms, mental health difficulties, metabolic problems and weight-related concerns.
Specific conditions mentioned in personal accounts include:
Digestive and intestinal problems: irritable bowel syndrome (IBS), diarrhoea, digestive discomfort and other persistent gastrointestinal symptoms.
Skin conditions: acne, psoriasis, eczema, rashes, hives and other skin complaints.
Joint, muscle and pain conditions: joint pain, knee pain, back pain and other persistent pain.
Inflammatory and autoimmune conditions: autoimmune disease, rheumatoid-type joint problems and other conditions involving inflammation.
Neurological conditions and symptoms: multiple sclerosis (MS), vision problems, migraines and other neurological complaints.
Mental health difficulties: depression, anxiety, obsessive-compulsive symptoms and other reported psychological difficulties.
Metabolic and weight-related problems: obesity, prediabetes, type 2 diabetes and elevated blood triglycerides.
Allergies and recurring complaints: seasonal allergies, frequent colds and other recurring symptoms.
Other reported health problems: fatigue, excessive sweating, bad breath, tooth sensitivity, athlete’s foot and certain chronic or unexplained symptoms.
These accounts describe people whose health problems improved or disappeared after they removed plant foods from their diets. In some cases, people report that symptoms returned when they reintroduced certain foods. Such experiences provide evidence that their diets were connected to their symptoms and raise the possibility that particular plant foods or compounds were contributing to their problems. The precise mechanisms may not always be known, and individual responses differ, but the reported improvements should not be dismissed simply because every underlying mechanism has not yet been established. [4]
Symptoms and the Elimination of Plant Foods
One possible explanation for symptoms associated with particular foods is that an individual does not tolerate one or more components of those foods well. Plants contain numerous compounds, including substances involved in their natural defence mechanisms. They also contain fibres, carbohydrates and other components that people digest and tolerate differently.
For someone who experiences symptoms associated with particular foods, removing those foods may reduce the factors contributing to the problem. However, an improvement following the removal of plant foods does not, by itself, establish that plant toxins were responsible. Several dietary components may have been removed at the same time.
This distinction matters. A person may report that digestive symptoms improve after eliminating vegetables, grains, nuts and seeds, for example. That observation is relevant even if the precise cause remains unknown. The symptoms might relate to particular plant compounds, fermentable carbohydrates, fibres, an individual food intolerance or a combination of factors.
It is also possible that a change in the overall composition of the diet, rather than a single compound, contributes to the improvement. A careful discussion should therefore recognise the reported result without assuming that the mechanism is already established.
Skin Problems, Joint Pain and Other Longstanding Symptoms
Some people describe improvements in skin complaints, joint pain and other longstanding symptoms after changing their diets. They may have tried different approaches for years before discovering that eliminating plant foods appeared to make a difference for them.
For example, individuals have reported improvements in acne, psoriasis and back pain after adopting a carnivore diet. Some have also described symptoms returning after consuming particular foods again.
Such accounts illustrate an important aspect of dietary experimentation: people may notice not only improvements after removing foods, but also changes when they eat them again.
These experiences should not be interpreted as proof that plants cause these conditions in everyone, or that plant elimination is an established treatment for them. They do, however, illustrate why the possibility of individual food-related symptoms should not be dismissed simply because a food is generally considered healthy.
A food can be nutritious and well tolerated by one person while being associated with unwanted symptoms in another. General dietary recommendations cannot necessarily predict how every individual will respond to every food.
What Happens When People Eat These Foods Again?
Some people who follow an elimination diet report that symptoms return when they reintroduce foods they previously removed. When the same pattern occurs repeatedly, it may provide a useful indication that a particular food or dietary component is associated with their symptoms.
For example, a person may report feeling better without grains and then notice a return of symptoms after eating them again. Another may report that particular vegetables, nuts or seeds appear to cause problems.
The interpretation depends on the circumstances. Symptoms can fluctuate naturally, and changes may be influenced by several factors. A personal account cannot establish the exact biological mechanism, but a consistent relationship between a food and a symptom may justify further investigation.
Anyone investigating suspected food triggers should consider a structured approach rather than drawing conclusions from a single episode. Reintroduction may not be appropriate when a food has previously caused a serious allergic reaction, and people with significant or persistent symptoms should seek appropriate medical advice.
Does This Mean Everyone Should Avoid Plants?
No. People differ in their tolerance of foods, and the experiences of people following a carnivore diet do not establish that everyone benefits from eliminating plants.
Some people eat a wide variety of plant foods without noticing problems. Others report that particular foods are associated with symptoms, and some describe substantial improvements after removing plant foods altogether.
Both experiences can exist without contradiction. The fact that many people tolerate a food does not prove that everyone will tolerate it equally well. Equally, the experience of one person who improves after eliminating a food does not establish that the food is harmful to everyone.
The relevant question for an individual is not simply whether a food is generally regarded as healthy, but also whether that person tolerates it and how they respond to eating it.
What Can We Conclude?
Plant defence compounds provide one possible area of investigation when considering why some people report symptoms associated with plant foods. However, the effects of eliminating plants cannot automatically be attributed to those compounds alone.
The experiences described by people following a carnivore diet illustrate a broader point: changing what we eat can be followed by changes in how we feel, and those changes may be meaningful even when their precise causes have not been established.
These accounts are personal experiences, not controlled clinical trials. They cannot independently prove that plant toxins caused a particular condition or that a carnivore diet is an appropriate treatment for everyone. Their value lies in documenting what individuals report experiencing and in raising questions that warrant careful consideration.
For people who experience persistent symptoms, it may be worth investigating whether particular foods contribute to them, with appropriate professional guidance where necessary. The aim should be to understand individual responses rather than to assume that all plant foods are harmful or that all people need to avoid them.
Ultimately, an informed discussion of plant foods should consider their nutritional properties, the defensive compounds they contain, differences in individual tolerance and the possibility that some people may experience improvements when particular foods are removed. Looking at all these aspects together provides a more complete picture than considering any one of them in isolation.
16. How should arguments about plant toxins be evaluated?
Arguments that plant defence chemicals contribute to modern chronic disease often begin with legitimate scientific findings. They may suggest that many chronic illnesses are better understood as the result of plant toxicity and malnutrition rather than as separate diseases, and that removing plant foods can address these underlying causes.
Several parts of this argument begin with established observations:
Plants produce chemical compounds that can defend them against predators and pathogens.
Some naturally occurring plant compounds can be toxic to humans.
Certain plant compounds can interfere with nutrient absorption.
Particular lectins can cause gastrointestinal illness when foods are inadequately prepared.
Some naturally occurring toxins can cause serious harm after acute or repeated exposure.
Individual people can experience adverse reactions to specific foods.
The question is how far these findings can be extended.
The research discussed above does not establish that plant toxicity is a general cause of modern chronic disease.
For example, a study showing that a particular lectin can damage intestinal cells does not prove that ordinary consumption of foods containing that lectin causes autoimmune disease. A study investigating the vagus nerve in Parkinson's disease does not establish that plant lectins cause Parkinson's disease. A list of naturally occurring carcinogens does not demonstrate that eating vegetables causes cancer.
Each of these claims requires evidence specific to the proposed effect.
This does not mean that the underlying questions should be dismissed. It means that the evidence must be examined carefully and that the conclusions should not go further than the studies support.
17. Could plant toxins be one reason people develop chronic disease?
It is reasonable to investigate whether particular dietary compounds contribute to particular health problems. Food can affect health through many mechanisms, including toxicity, allergies, nutrient availability and metabolic effects.
There are established examples of dietary substances causing illness. There are also foods that need careful preparation because they contain naturally occurring toxins.
However, chronic diseases usually involve complex interactions between genetic, environmental, metabolic and behavioural factors. Demonstrating that a chemical can affect a biological process does not establish that it is a major cause of a particular disease in the general population.
To establish that a plant compound contributes to chronic disease, researchers need evidence linking realistic exposure to meaningful health outcomes. Stronger evidence may come from a combination of mechanistic studies, well-designed human observational research and clinical trials where appropriate.
It is also important to investigate whether reducing exposure improves outcomes, and whether any benefits are specific to certain people or apply more widely.
The scientific question should remain open to evidence, but a plausible mechanism is not the same as proof of causation.
18. Do plant toxins shorten human lifespan?
Some arguments about plant toxins also raise the possibility that human beings could live to around 120 years and that modern dietary practices may contribute to people failing to reach their potential lifespan.
The existence of plant toxins does not establish this connection.
Some toxins can cause serious illness or death. Some can produce chronic effects under particular exposure conditions. Those facts are well established for specific compounds. [1]
However, the evidence discussed on this page does not demonstrate that ordinary consumption of properly prepared plant foods shortens human lifespan as a general rule. Nor does it demonstrate that eliminating all plant foods allows people to live to 120.
To establish such a claim, researchers would need evidence directly linking specific dietary exposures to reduced longevity, while accounting for other influences on lifespan. They would also need evidence that reducing those exposures improves long-term survival.
A maximum possible human lifespan, an average life expectancy and the number of years a person lives in good health are different measures. They should not be treated as interchangeable.
The claim that avoiding plant toxins extends human lifespan remains unproven.
19. What should we conclude from the research?
The scientific evidence supports several important conclusions.
Plants do produce chemical defence compounds. These are part of plant biology and have been studied extensively.
Some plant toxins can harm humans. Examples include active lectins in inadequately cooked kidney beans, cyanogenic compounds in improperly processed cassava and elevated glycoalkaloids in certain potatoes. These are genuine food-safety concerns. [1, 5, 7]
Some plant compounds affect nutrient absorption or biological processes. Phytate, oxalate and certain lectins are examples, although the significance of these effects depends on the substance, exposure and individual circumstances. [5, 6]
Some proposed effects on chronic disease remain uncertain. Laboratory findings and plausible mechanisms can help guide research, but they do not automatically demonstrate that ordinary consumption of plant foods causes chronic disease in humans.
The claim that all plant foods are harmful is not established by the existence of plant toxins. Nor is the claim that a carnivore diet is necessary for everyone or that eliminating plant foods extends lifespan to 120 years.
Tea and coffee also illustrate why each substance needs to be examined separately. Caffeine has well-established effects on alertness and sleep; unfiltered coffee can raise blood cholesterol through its diterpene content; tea can affect non-haem iron absorption; and drinking beverages at very high temperatures raises a separate concern. These findings do not establish that either beverage is universally harmful. They demonstrate the importance of considering specific compounds, exposure levels and evidence from human studies.
The appropriate conclusion is neither that every plant food is harmless nor that all plants should be considered poisonous. It is that plant compounds differ considerably, and their effects need to be assessed individually.
Understanding these differences allows a more informed discussion of food, nutrition and health than relying on the labels natural, healthy or toxic alone.
Our approach at Healing by Nutrition
At Healing by Nutrition, we are interested in how different dietary approaches affect people in everyday life. Our own experience has led us to explore low-carbohydrate nutrition, animal-based foods and strength training.
We recognise that individual experiences can be meaningful, but we also believe that scientific claims should be examined carefully. A compound's presence in a food, a laboratory result and a demonstrated effect on human health are three different things.
We encourage people to understand what they eat, consider their own circumstances and seek appropriate professional advice when making significant dietary changes.
Our nutrition and training programmes focus on practical choices, individual goals and consistency. We do not present our experience as a substitute for medical assessment, and we do not claim that one dietary approach is suitable for everyone.
Medical disclaimer
This page is provided for general educational purposes only. It is not intended to diagnose, treat, cure or prevent any disease and should not be considered a substitute for individual medical advice.
Healing by Nutrition is not a medical service. Our information and programmes are based on practical experience and general educational information; they do not replace assessment or treatment by a qualified healthcare professional.
If you have a medical condition, a history of kidney stones, a food allergy or other dietary restrictions, or if you are considering a major change to your diet, consult an appropriately qualified healthcare professional where necessary. Do not stop or change prescribed medication without advice from the healthcare professional responsible for your care.
Scientific References
[1] World Health Organization. (2023). Natural toxins in food. Fact sheet, 10 March 2023.
[2] Ames, B. N., Profet, M. and Gold, L. S. (1990). “Dietary Pesticides (99.99% All Natural).” Proceedings of the National Academy of Sciences of the United States of America, 87(19), 7777–7781.
[3] Ames, B. N. and Gold, L. S. (1990). “Dietary Carcinogens, Environmental Pollution, and Cancer: Some Misconceptions.” Medical Oncology and Tumor Pharmacotherapy, 7(2–3), 69–85.
[4] No Carb Life (@zerocarb). YouTube interviews featuring personal accounts of health problems and reported changes after adopting a carnivore diet.
[5] European Food Safety Authority (EFSA). (2026). Risks for Human Health Related to the Presence of Plant Lectins in Food. Scientific assessment and plain-language summary.
[6] Mitchell, T., Kumar, P., Reddy, T., Wood, K. D., Knight, J., Assimos, D. G. and Holmes, R. P. (2019). “Dietary Oxalate and Kidney Stone Formation.” American Journal of Physiology—Renal Physiology, 316, F409–F413.
[7] European Food Safety Authority (EFSA). (2020). Glycoalkaloids in Potatoes: Public Health Risks Assessed.
[8] Svensson, E., Horváth-Puhó, E., Thomsen, R. W., Djurhuus, J. C., Pedersen, L., Borghammer, P. and Sørensen, H. T. (2015). “Vagotomy and Subsequent Risk of Parkinson’s Disease.” Annals of Neurology, 78(4), 522–529.
[9] Liu, B. et al. (2017). “Vagotomy and Parkinson Disease: A Swedish Register-Based Matched-Cohort Study.” Neurology, 88(21), 1996–2002.
[10] European Food Safety Authority (EFSA). (2015). “Scientific Opinion on the Safety of Caffeine.” EFSA Journal, 13(5), 4102. DOI: 10.2903/j.efsa.2015.4102.
[11] US National Institutes of Health, Office of Dietary Supplements. Fluoride: Fact Sheet for Health Professionals.
[12] International Agency for Research on Cancer (IARC). (2018). Drinking Coffee, Mate, and Very Hot Beverages. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Volume 116.
[13] Urgert, R. et al. (1996). “Comparison of Effect of Cafetière and Filtered Coffee on Serum Concentrations of Liver Aminotransferases and Lipids: Six Month Randomised Controlled Trial.” BMJ, 313, 1362–1366.
[14] US National Cancer Institute. Acrylamide and Cancer Risk.
[15] European Food Safety Authority (EFSA). Furan in Food: Risks Assessed. Scientific assessment of furan and methylfurans in food.
[16] Cai, L., Ma, D., Zhang, Y., Liu, Z. and Wang, P. (2012). “The Effect of Coffee Consumption on Serum Lipids: A Meta-Analysis of Randomized Controlled Trials.” European Journal of Clinical Nutrition, 66, 872–877.
[17] World Health Organization. (2025). Traditional Medicine. Questions and Answers, 28 November 2025.
[18] World Health Organization. (2023). Traditional medicine has a long history of contributing to conventional medicine and continues to hold promise. 10 August 2023.
[19] U.S. Food and Drug Administration (FDA). (2024, August 29). What Is a Botanical Drug? Center for Drug Evaluation and Research (CDER).
[20] Agency for Toxic Substances and Disease Registry (ATSDR). Module One – Introduction to Toxicology. Toxicology Curriculum for Communities Trainer's Manual.