When it comes to concerns about high-carbohydrate foods, many people in recent years have focused on gluten, a protein found in wheat and some other grains, which they deem responsible for countless common ills (even though only a small percentage of people are truly sensitive to it). Now the villains du jour are lectins, which are ubiquitous carbohydrate-binding proteins found notably in plant foods such as legumes and whole grains, but also in animals and microorganisms. Like gluten, plant lectins get blamed for a laundry list of woes, from inflammatory diseases and obesity to cancer, arthritis, and gastrointestinal problems.
Leading the charge against lectins has been Dr. Steven Gundry, whose 2017 book The Plant Paradox is subtitled “The Hidden Dangers in ‘Healthy’ Foods That Cause Disease and Weight Gain.” The scare (or sneer) quote marks around “healthy” are the key to that subtitle suggesting that the plant foods you thought were good for you are making you sick. Other books followed, including a lectin-avoidance cookbook, as well as Dr. Gundry’s own line of pricey dietary supplements (including one called Lectin Shield), resveratrol-spiked chocolate ($75 for 8 ounces), and anti-aging creams and serums ($100 each), all somehow linked to his anti-lectin, happy-gut crusade and promoted by provocative ads and infomercials (often disguised as health news articles) on major websites. Dr. Gundry claims that lectins are “the #1 biggest danger in the American diet” and that “everything you thought you knew about your diet, your health, and your weight is wrong.” Those are just two of his many over-the-top contrarian claims.
Lectins are hardly a new bogeyman. In fact, starting two decades ago, proponents of the highly dubious “Eat Right for Your Blood Type” diet linked lectins to all sorts of adverse reactions, depending on one’s blood type.
Here’s a look at the claims and facts about lectins.
Claim: Lectins are toxic components of plant foods.
Fact: Some can be, under rare circumstances, but not when foods are consumed the way they are customarily prepared.
Lectins are a large and diverse class of carbohydrate-binding proteins that perform a variety of important biochemical functions and are especially high in legumes and wheat. (Legumes refer to a family of plants, or to the fruits or seeds of such plants, and include most beans, lentils,and chickpeas.) Plants have evolved to produce sophisticated, multilayered systems and compounds to defend themselves against insect, microbial, and animal attack. Lectins are key defenders for plants and, like other “natural pesticides,” end up in foods we eat. Keep in mind that plant foods contain thousands of compounds that could have good or bad effects in people who consume them.
Some of the lectins in certain raw legumes (notably kidney beans) can indeed be harmful, even dangerous, for humans. But when legumes are cooked, fermented, sprouted, or processed for canning, the lectins bind to various carbohydrates, which deactivates their toxic potential, and they pass through the digestive tract and are eliminated. In contrast, eating raw or undercooked legumes allows lectins to remain unbound and to latch on to cells in the intestinal walls, which can result in symptoms similar to food poisoning—vomiting, diarrhea, and abdominal pain—and may even require hospitalization. But who eats raw or semi-raw beans, except perhaps by accident? It’s no surprise that lab animals fed certain raw legumes or large quantities of isolated lectins have experienced intestinal damage in studies, but that’s not the way humans consume lectins.
Claim: Lectins cause inflammation and inflammatory diseases.
Fact: Certain isolated lectins may promote inflammation in lab animals, but human research shows that legumes and whole grains, in the context of largely plant-based diets, reduce markers of inflammation and are associated with a reduced risk of diseases in which inflammation plays a role, such as coronary artery disease and rheumatoid arthritis.
Claim: Lectins promote weight gain.
Fact: Numerous studies have found that a diet rich in plant-based foods, including legumes and whole grains, isn’t associated with weight gain. In fact, studies show that consumption of legumes and whole grains is associated with healthy body weight and lower body fat. According to an analysis of 21 clinical trials, published in the American Journal of Clinical Nutrition in 2016, eating legumes “may be a beneficial weight-loss strategy because it leads to a modest weight-loss effect even when diets are not intended to be calorically restricted.”
Claim: Lectins cause cancer.
Fact: Lectin-rich foods may reduce the risk of certain cancers, laboratory research and observational human studies suggest. According to a review paper in the Journal of Cereal Science in 2014, lectins may have a variety of anticancer effects, such as inducing tumor cell suicide (apoptosis). In cancer cells, lectins appear to bind to the carbohydrates in the cell membrane, altering cell signaling—and, as a result, may have an anticancer effect. That’s why researchers are studying various lectins as candidates for anticancer, antimicrobial (including anti-HIV), and other drug therapies.
If there’s one thing evidence-based health and nutrition experts agree on, it’s that people should eat a largely plant-based diet. For those looking for an excuse not to do so, Dr. Gundry offers a contrarian, pseudoscientific voice. But he is wrong—and self-serving, in that he wants to sell you dietary supplements containing the nutrients you’d miss out on if you followed his diet.
It’s ironic that legumes, whole grains, and other plant foods are blamed for today’s health problems when relatively few Americans are eating significant amounts of them, opting instead for refined grains, red meat, sweets, and processed foods that are all low in lectins. The healthiest diets in the world, eaten by the longest-lived people, are largely vegetarian and include legumes and whole grains. The same is true of the Mediterranean diet, the anti-hypertension DASH eating plan, the cholesterol-lowering Portfolio diet, and most diets recommended for people with diabetes.
Still, it’s only common sense to avoid eating raw or undercooked dried beans in order to avoid gastrointestinal distress. In particular, if you prepare dried beans in a crockpot or slow cooker, make sure they are cooked adequately to deactivate the lectins (follow directions provided with the pot or recipes). Canned beans are already cooked.
This article first appeared in the UC Berkeley Wellness Letter
Also see How to Buy Beans.