A book published in 2017 by Steven Gundry, MD called “The Plant Paradox” makes the startling claim that lectins are the cause of most human disease. If this is true it would indeed be ground breaking. But, if it is true, how can we explain the wealth of evidence that we have about the healthiness of plant-based diets? Or the extreme longevity of societies that have eaten high-lectin foods for decades, even centuries. Or the well-established link between consumption of whole grains or legumes and the reduced risk of many of the chronic diseases that plague our society today? In fact evidence for the wholesomeness of lectin-containing foods is prodigious and has been replicated again and again over many decades of study.
What are lectins?
Lectins are specialized proteins produced by both plants and animals for the purpose of self-protection and are present in most of the foods that human beings consume (43). Legumes (particularly beans, soybeans and peanuts) and whole grains have the largest lectin content followed by dairy products, seafood and plants of the nightshade family (such as tomatoes, potatoes, peppers and eggplant).
Organisms that are part of the animal kingdom have options when faced with danger. They can protect themselves by flight (leaving the dangerous area) or by fight (using teeth, claws or hooves to discourage or overpower the predator). Plants cannot run away but they have developed systems to fight for their survival. Plants synthesize toxic substances that ward off threats from insect and animal predators as well as from bacteria, viruses, fungi and other parasites. Lectins are one type of these dedicated natural disease fighters. Lectins protect plants by combining with specific carbohydrates originating either from the invading organism or from damaged plant cell wall structures and, through various processes, neutralizing the risk (11). Phytonutrients such as phenols and flavonoids are other components produced by plants that provide protection to the plant through different mechanisms (12).
Are lectins toxic?
Many lectins are non-toxic, including those found in tomatoes, lentils, peas, chickpeas, broad beans and other common foods (19). Fortunately lectins that have the ability to produce toxic effects are easily destroyed by proper cooking techniques. The only lectin known to cause distress in humans is phytohaemagglutinin (PHA) which is found in raw beans, especially red or white kidney beans. This lectin can bind to a carbohydrate present on human intestinal cells and cause mild to moderate symptoms including intestinal gas overproduction, vomiting, cramping and diarrhea. As few as four or five raw beans can trigger symptoms.
Phytohaemagglutinin is easily inactivated by proper cooking. In fact, cooking beans long enough to make them soft enough to eat destroys virtually all of their lectin activity (21,23). Research has shown that dried beans need to be actually boiled before eating. Dry heat such as baking will not completely eliminate potential lectin toxicity. One study found that, if dried beans are not pre-soaked, it takes about an hour of boiling to destroy all the lectin activity. If they are first soaked overnight, 98% of the lectin activity is gone after fifteen minutes of boiling and the rest disappears after half an hour (26). Another trial recommends soaking beans in water for at least five hours and then boiling them for a minimum of ten minutes. After such treatment the lectin activity will be gone although the beans will still not be soft enough to eat. It takes about one hour of boiling before beans are actually edible (1,20,21). No need to worry about canned beans either. The canning process cooks beans sufficiently to detoxify any lectins in the food (22,27). So relax and enjoy your beans. As long as they are cooked properly, lectins in beans are not an issue.
Are lectins beneficial?
Beans aside, humans do consume lectins. Because lectins are a component of many foods in the human diet, intake of lectins can be significant. For instance, studies have detected low levels of lectins in roasted peanuts and tomatoes and subsequently in the bloodstream of people who eat them (33,34,35). This is not something to worry about however. In fact, lectins seem to have significant beneficial effects for human health. Low doses of lectins can stimulate gut function, limit tumour growth and cause regression of cancers, inhibit angiogenesis (growth of the new blood vessels that cancers require for their growth) , modulate immune system response, boost healing, protect against viruses and other harmful micro-organisms and reduce obesity (28,29). During the 1960s researchers looking into the lectins in wheat germ demonstrated that lectins could distinguish between cancer cells and normal cells, clumping tumour cells together while leaving the normal cells alone (30). Later it was determined that lectins can actually suppress the growth of cancerous cells. Studies on white kidney bean lectin showed its ability to hinder the growth of cancer cells in a petri dish including cells from human head and neck cancers, liver cancers, breast cancers and cervical cancers (29,31). Additionally lectins can induce apoptosis (cell death) and autophagy (the process through which cells eradicate their dysfunctional components) in human liver, bladder, pancreatic and skin cancer cells (3). Lectins have even shown potential in rehabilitation of cancer cells, returning malignant colon cancer cells back into normal growth patterns (32). Many studies show that people who eat more beans and whole grains tend to get less cancer overall (8). The authors of a 2005 review on lectins and cancer state, “Plants contain numerous physiologically active components, or phytochemicals, that can alter the biochemical pathways associated with cancer initiation, promotion or progression. Among the phytochemicals that are being intensively studied for their role in cancer chemoprevention and progression are the lectins.” (19).
Besides the inhibitory role of lectins in cancer, foods high in lectins are associated with many additional beneficial effects. A review by the Journal of Cereal Science in 2014 reported that consumption of grains that contain lectins such as wheat germ agglutinin is associated with significantly reduced risks of type 2 diabetes, cardiovascular disease and some types of cancer and promotion of favourable long-term weight management (2). In 2017, a review and meta-analysis of prospective cohort studies was undertaken to explore the association between dietary legume consumption and cardiovascular disease risk. The review encompassed fourteen studies and 367,000 people. Results showed that those who ate the most legumes had a 10% decreased risk of cardiovascular disease and coronary heart disease (13). A study on obese people who consumed 4 servings of legumes weekly showed a 40% reduction in C-reactive protein levels, a very significant drop in this major indicator of systemic inflammation. Weight loss and decreases in total cholesterol and blood pressure independent of weight loss also occurred (24). Tomatoes are members of the nightshade family and are high in lectins. A randomized interventional trial showed that ingestion of tomato juice resulted in reduced inflammation throughout the body, reduced inflammatory mediators and reduced cholesterol levels (9). Tomatoes are also high in the phytochemical, lycopene, which is responsible for a number of cardiovascular benefits including lower risk of heart attack and stroke and decreasing LDL levels as well as lowering the tendency of LDL-cholesterol to oxidize thereby inhibiting the development of atherosclerosis (14,15,16). Low blood lycopene is associated with increased risk of atherosclerotic events such as coronary blood vessel blockage and stroke and a greater risk of premature death (17,18).
Blue Zones can also teach us about how to live longer. Blue Zones are defined societies found in certain areas around the world that consist of extremely healthy people who enjoy the longest lives of any population on the planet (7). The common thread among Blue Zones is the consumption of legumes, including beans, split peas, chickpeas and lentils. Legumes in fact are the most important dietary predictor of survival in older people around the world. A large study of 785 participants followed over seven years showed that each 20 gram increase in daily intake of legumes resulted in a 7 to 8% reduction in early death (6). If you look at the science, all whole plant foods, including the foods that are highest in lectin content, are associated with longer length of life. Risk of all-cause mortality decreases with increasing intake of whole grains, legumes and other vegetables, fruits and nuts. Choosing foods almost exclusively from these food groups confers a 56% reduction in all-cause mortality in spite of the high concentration of lectins in many of these foods (25). Other benefits of such a diet include lower risk of cardiovascular disease, type-2 diabetes and cancer (25,4,5).
What would be the consequences of following a lectin-free diet?
Taken directly from the website of Dr. Steven Gundry, author of the book “The Plant Paradox”, the following foods would be removed or severely curtailed in the quest for a lectin-free diet (10);
Beans and legumes
Peanuts and other nuts
Squash, pumpkins and zucchini
Vegetables from the nightshade family – tomatoes, potatoes, any kind of pepper and eggplant
Fruit, unless it is in season
Cow’s milk purchased from regular grocery outlets
What is left to eat? Pasture raised meat. Chicken and turkey. Seafood. Eggs. Milk from goats, buffalo or cows from Southern Europe. Some vegetables such as sweet potatoes, leafy greens and cruciferous vegetables (broccoli, cauliflower and Brussels sprouts), asparagus, celery, garlic and onion. Mushrooms. Avocados. Olive oil. (10)
(Note that foods such as sweet potatoes, carrots, leaks, garlic, onion, mushrooms, oats, rice, avocados, salmon and shellfish such as crab and snails also contain significant amounts of lectins but they are not listed as foods to avoid by Dr.Gundry.)
A person eating lectin-free would not reap the health advantages of consuming legumes or whole grains, the foods most associated with thriving into old age. Most fruit would be off-limits, removing one of the most concentrated and delicious sources of health-producing antioxidants. Meals would center around animal-sourced food and it is well known that such a diet leads to obesity, diabetes, cardiovascular disease, impaired kidney function, cancers of the breast, colon and prostate and higher rates of early death from all causes (36,37,38,39,40,41,42).
Lectins are nothing to worry about
Whole grains, beans and other legumes, all vegetables, fruits, seeds and nuts are high-nutrient, fiber-rich foods that are consistently associated with a long, healthy life. If lectins indeed have any negative effect on health it is vastly overpowered by the proven benefits of whole plant foods. Make the overwhelming evidence of the power of whole plant foods to produce vibrant health throughout life be your guide when it comes to choosing what you eat.
If you are interested in looking into Dr. Gundry’s book, “The Plant Paradox”, I suggest that you read the detailed review and assessment written by eminent nutrition researcher, T. Colin Campbell PhD. He delved deeply into Dr. Gundry’s claims and found severe problems with misrepresented evidence or complete lack of scientifically valid evidence altogether. You can find this article on-line at https://nutritionstudies.org/the-plant-paradox-by-steven-grundy-md-commentary/
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