Evidence of long data suggests that consuming a diet rich in plant-based foods plays a significant role in the prevention and reduction of chronic diseases, such as cardiovascular disease, cancer, stroke, dementia, diabetes, cataracts and others. Well-researched dietary models including Mediterranean, dietary approaches to stop hypertension (DASH), vegans and vegetarians, as well as the hunter-gatherer diet (Paleolithic), all ample amounts of whole foods in a certain capacity, including fruits, vegetables, nuts, legumes and / or whole grains. Some specific aspects of these eating patterns may differ, all of which encourage a variety of nutrient-rich, unprocessed plant foods and reduced consumption of processed grains, added sugars, and table salt. Plant-based foods, in addition to micro and macronutrients, contain significant concentrations of bioactive plant compounds. Research shows that the reduction in chronic disease risk can be attributed to the synergistic effects of these anti-inflammatory phytochemicals, including an endless array of polyphenols, alkaloids, carotenoids, organosulfuric compounds, terpenoids and phytosterols.
Due to the different and interactions of vitamins, minerals and phytochemicals in a single food, the health effects of a whole food or a combination of foods will be more different than those of isolated compounds. To further complicate the research, the interaction of phytochemicals and microbiota within the gut environment could alter both bioavailability and biological effects. More recently, various researches have questioned the healthiness of plant foods due to the presence of certain compounds, called “anti-nutrients”. These purported antinutrients, which include lectins, oxalates, phytates, phytoestrogens and tannins, are believed to limit the bioavailability of key nutrients, while other studies conclude that they may have health promoting effects.
What are lectins?
Lectins are proteins in plants that studies have linked to both positive and negative health effects. Some experts have put forward the idea that a lectin-free diet may benefit health, but the available research does not support this claim. Some plant-based foods – such as beans and legumes, whole grains, and some vegetables – contain a high amount of lectins. Lectins have some links to inflammation, and researchers have studied excluding them to manage specific health problems, such as multiple sclerosis (MS). Lectins are a type of protein that, in humans, can promote cell development and support communication between cells. They also play a role in the human immune response. There are several types of lectins. Lectins can impact health in many ways, from digestion to the risk of chronic disease. Research has also shown that they cause clumping in red blood cells. Research does not currently support any of the purported health benefits of the lectin-free diet. Some doctors classify lectins as anti-nutrients, as they block the absorption of certain nutrients.
The type of lectin found in red beans is called phyto-hemagglutinin (PHA). It is responsible for red bean poisoning, which results from the consumption of raw or undercooked beans. According to the Food and Drug Administration (FDA), consuming just four raw beans could cause symptoms such as severe nausea, vomiting, and diarrhea. If a person has digestive enzyme deficiencies, consuming excess lectins can lead to nutritional deficiencies and digestive problems. This is because the body cannot break down lectins. Instead, they bind to the nutrients and cells that line the gastrointestinal tract. However, lectins often attach themselves to carbohydrates and leave the body before they can cause harmful effects. This action on carbohydrates has led to some laboratory studies suggesting that the lessons could influence the growth of cancer cells. Indeed, a few years ago, research proved that some lectins bind to insulin and growth factor EGF receptors, blocking them. The nutrients that accompany lectins in plant-based foods are also essential, and removing them from the diet can have harmful consequences.
Properties of Lectins
Although lectins are quite resistant to enzymatic digestion in the gastrointestinal tract, they can be removed from food by various processes. For example, soaking, autoclaving, and boiling cause irreversible denaturation of the lectin. Boiling the legumes for one hour at 95 ° C reduced the haemagglutinating activity by 94–99.8%. Even the boiling of red and white beans, notoriously rich in phytohemoggluttinin (PHA), leads to the complete elimination of lectins. Microwave ovens, on the other hand, are not an effective method for deactivating lectin. While the microwave destroys the hemagglutinins in most legume seeds, it does not significantly affect the lectins in common beans. Furthermore, fermentation beyond 72 hours has been shown to destroy almost all lectins in lentils (Lens culinaris)
The lectin-free diet
Dr. Steven Gundry coined the term “lectin-free diet”. Dr. Gundry is a former heart surgeon who has shifted his focus to food and supplement medicines. He describes lectins as the main danger in the Western diet. He then wrote a book that provides information on how to avoid classes, alternative food choices and recipes. According to the book, Dr. Gundry’s plan helps people improve their health and reduce their body weight. However, no evidence supports the exclusion of lectins from the diet outside of a specific diet. For most people, the health benefits of a lectin-free diet are unclear. However, removing lectins from the diet has proved beneficial for groups of people with specific conditions. For example, a 2019 review of studies found that a lectin-free diet may benefit people with Crohn’s disease and multiple sclerosis.
However, research has not yet confirmed its benefits for the wider population. Additionally, the lectin-free diet is a restrictive plan, which can make it difficult for some people to follow it in the long term. The plan also limits or eliminates many nutritious foods, such as beans and certain vegetables. The lectin-free diet bears similarities in principle to another eating style dating back two decades, called the “blood group diet”. Promoted by the American doctor Peter d’Adamo and in Italy by Dr. Mozzi, this food protocol recognizes the principle whereby each vegetable and animal protein acts as a “lectin” according to the blood group of the person who ingests it.
This is because there would be a molecular mimicry between certain dietary proteins and real lectins: many lectins are proteins with carbohydrate chains (glycoproteins), as are the antigens of red blood cells (A, B, AB and 0). Just as lectins agglutinate red blood cells, digestive protein fragments could also do the same and interact with red blood cell antigens, and cause clumping. In the diet of the blood group, much emphasis is given to the ability that lectins or proteins “harmful” to the group, the phenomenon of insulin resistance. That is, proteins or their digestive fragments not tolerated by the specific group can interfere with the function of the pancreas and cause the body to accumulate fat. Further confirmation comes from a study carried out in 2017 by a group of researchers from the Chinese Academy of Sciences, who wanted to understand how lectins can cause silent and so widespread inflammatory reactions.
Since lectins are not very digestible by the body, it is very likely that they can trigger autoimmune diabetes, rheumatoid arthritis, Crohn’s disease and more. But how they do it has always remained obscure. The team found that like whole proteins, lectins can be incorporated by cells into lysosomes, the ‘intestines’ of cells. But even there they are not degraded: thus they begin to disrupt the flow of calcium inside the cells and activate a protein complex that researchers now know very well: the inflammosome. It is responsible for the non-bacterial inflammations that appear in familial Mediterranean fever, gout, rheumatoid arthritis, arthritis with no apparent cause and in diets rich in fat, just to name the most well-known conditions. According to what the researchers have discovered, the logical and molecular basis of the potential injuries that lectins can cause to health are more than justified.
Requirements and issues
A lectin-free diet can be difficult to follow not only for normal people, but also for vegetarians or vegans, as legumes, nuts, seeds, and whole grains provide plant-based protein. Legumes, whole grains, and fruit and vegetable peels also provide dietary fiber. A lectin-free diet can cause constipation if dietary fiber intake decreases. Dr. Gundry recommends the following foods for people wishing to limit their lectin intake: pasture-raised meats, casein-modified (A2) milk, cooked sweet potatoes, leafy greens, broccoli and Brussels sprouts, asparagus and celery, garlic and onions, mushrooms, avocados, olives or extra virgin olive oil.
On the other hand, people may want to limit the following foods when trying to avoid lectins: squash, legumes, including beans, peas, lentils, and peanuts; solanaceae, such as aubergines, peppers, potatoes and tomatoes, fruit, although the diet allows for a moderate amount of seasonal fruit and cereals. If a person wants to consume wheat, the plan recommends white flour products instead of wheat. Additionally, following a lectin-free diet can be expensive, as the plan recommends specialty milk, pasture-raised meat, and expensive supplements.
Although lectins can cause some harm to people with intolerance or if people eat them in excess, strong research exists to support the benefits of consuming plant foods. Some people with MS or inflammatory bowel disease may benefit from limiting dietary lectins. However, current evidence does not support this diet as a general tool for weight management. Many plants are rich in lectins. However, lectin levels can differ significantly between plant types. There are also many types of lectins, and some appear to provide health benefits. It is also important to note that much of the research on lectins has been conducted through animal or test tube studies. No recent research supports excluding them from most diets. Additionally, many studies have looked at individual lectins instead of the foods that contain them. More research is needed before doctors can recommend following a lectin-free diet. For further information, you can consult the article on this website: “Allergia alle solanacee: il dito puntato su pomodori, patate e melenzane”.
- Edited by Dr. Gianfrancesco Cormaci, PhD, specialist in Clinical Biochemistry.
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