Are Lectins Making People Fat?

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According to cardiologist Dr. Steven Grundy, not only do lectins make people fat, but lectins “…are the #1 Biggest Danger in the American Diet” (1). In addition to his website, Dr. Grundy warns about the supposed dangers of lectins found in whole grains, beans, and many other whole plant foods in his popular book, The Plant Paradox. Lectins are a type of protein found in many plant foods. There is no doubt that some lectins, especially those found in uncooked or undercooked beans can damage the lining of one’s gastrointestinal (GI) tract and this can cause some GI problems, especially if consumed in large amounts. However, because lectins are proteins, they get denatured by cooking. Soaking dry raw beans overnight and throwing away the water and then boiling them for 10-15 minutes denatures all the lectins found in beans that can cause GI problems. So whatever potential bean lectins may have to cause digestive problems can easily be eliminated by proper cooking and does not require the prolonged use of the pressure cooker Dr. Grundy says you must use to eat any beans.

Dr. Grundy’s claims that lectin-rich beans and other lectin-containing foods are dangerous to one’s health is completely at odds with the fact that people living in the 5 “Blue Zones” where people live longer and healthier lives than other parts of the world typically get about two-thirds of their total calories from whole grains, beans and starchy vegetables, all of which contain lectins Dr. Grundy tells us we must severely restrict to stay thin and healthy. These long-lived people reside on the Italian island of Sardinia, on the Japanese island of Okinawa, the Seventh Day Adventists living in Loma Linda, California, on Costa Rica's isolated Nicoya Peninsula, and on Ikaria, an isolated Greek island. In these 5 places, people tend to consume a largely plant-based diet and generally eat far more beans than the average American. Foods with little or no lectins include refined fats & oils, refined sugars, refined grains, and animal products including fatty red meats, dairy products, and eggs. That sounds like the typical American diet, and yet most Americans are overweight or obese while consuming fewer lectins than the much healthier and longer-lived people in the Blue Zones. Even more puzzling is Dr. Grundy’s claim that Americans can lose weight and get healthier by eating even more fatty animal products and refined plant oils and further restrict the intake of most minimally-processed plant foods. Contrary to Dr. Grundy’s claims that high lectin foods promote obesity, it is clear obesity is far less common in the 5 Blue Zones despite the fact that people in all these long-lived populations have a much higher intake of lectin-rich plant foods than the average American (2).

A Great Cardiologist Debate

Dr. Grundy had the misfortune of debating another cardiologist (Dr. Joel Kahn) on “The Doctors” TV show. Dr. Kahn explained that Dr. Grundy has never published any research data to support his questionable claims that dietary lectins, especially from beans, somehow promote obesity and numerous other ills. The Kahn-Grundy debate on that TV show is available here:

As Dr. Kahn pointed out in his one-sided debate with Dr. Grundy, the data from the recent PURE Study (3), which examined the health and diets of 18 populations around the globe found people who consumed more beans and other lectin-containing whole plant foods were healthier than those eating a diet more in sync with what Dr. Grundy recommends in The Plant Paradox. Indeed, the PURE Study data suggest eating more raw fruits and vegetables (which contain more lectins than cooked vegetables and fruits) was healthier than eating them cooked. How does Dr. Grundy explain this evidence? He doesn’t.

What Other Foods Besides Beans Contain Lectins?  

Whole grains including barley, corn, rice and wheat (especially the wheat germ) contain lectins. Indeed, wheat germ is consumed raw or lightly roasted and its lectins remain intact. In fact, many vegetables are consumed raw and even in fairly large amounts appear to cause only minimal GI problems, especially in people who are not used to eating them. Nevertheless, the lectins found in zucchini, carrots, rhubarb, beets, mushrooms, asparagus, turnips, cucumbers, pumpkin, sweet peppers and radishes whether cooked or consumed raw do not appear to cause significant GI problems. Citrus fruits such as oranges, lemons and grapefruit, along with berries, including blackberries, raspberries, and strawberries and many other fruits including pomegranate, grapes, cherries, quinces, apples, watermelon, banana, papaya, plums, and currants are also sources of dietary lectins. Lectins also are found in nuts and seeds such as walnuts, hazelnuts, peanuts, sunflower seeds, and sesame seeds. Chocolate, coffee and some spices, including caraway, nutmeg, peppermint, marjoram and garlic, are also sources of dietary lectins. Some of these lectins can escape being denatured or digestion by stomach acid and proteolytic enzymes and some do appear to get absorbed. Indeed, there is evidence that lectins found in wheat and other whole grains might improve GI health and possibly help reduce the risk of some cancers if consumed regularly (4).  For more information about why the potential health benefits of a diet high in these lectin-containing plant foods almost certainly outweighs any risk see Dr. Gregor’s excellent video on lectins (5).

Bottom Line: There is no debate that eating a lot of uncooked or undercooked beans can cause at least transient GI problems. However, those GI problems from excessive lectins would likely lead to weight loss. There is no evidence (that this reviewer is aware of) that supports any claims that dietary lectins somehow promote obesity. The preponderance of credible scientific evidence suggests eating a diet high in lectin-containing whole plant foods is far more likely to promote weight loss, better health, and longevity rather than obesity and the numerous other ills claimed by Dr. Grundy in The Plant Paradox. That was the only thing one could consider paradoxical about Dr. Grundy’s questionable thesis.

By James J. Kenney, PhD, FACN


  4. Fikrat I. Abdullaev FI and Gonzalez de Mejia. Antitumor Effect of Plant. Nat. Toxins 1997;5:157–63
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