Q:I’ve been seeing articles and books on the health benefits of a lectin-free diet. Is there any merit to these claims?

A: Americans constantly are bombarded with misinformation, and it’s especially tough to wade through the purported facts when the information is circulated by medical authorities such as physicians. Although the research on lectin, which is found primarily in nutrient-dense plant foods, is still emerging, preliminary studies have revealed potential health benefits of lectin consumption and minute evidence of harm.

The Controversy

Lectin is a carbohydrate-binding protein that can be found in varying amounts in most plants, including beans, pulses, grains, fruits and vegetables (eg, potatoes, tomatoes, sweet potatoes, zucchini, carrots, berries, watermelon), nuts, coffee, chocolate, and some herbs and spices (eg, peppermint, marjoram, nutmeg). Pulses and grains contain the highest amounts of lectin compared with other foods. Cooking destroys most of the lectin in foods and weakens its ability to bind to cells or causes it to bind to other compounds found in food.

The lectin-free diet has been popularized since cardiologist Steven Gundry, MD, FACS, FACC, released the New York Times bestseller The Plant Paradox: The Hidden Dangers in “Healthy” Foods That Cause Disease and Weight Gain in April 2017. The book promotes a lectin-free diet to treat medical conditions such as autoimmune diseases, allergies, and cancer. Supporters of the Bulletproof Diet also promote a lectin-free diet.

Gundry and other lectin-free diet promoters believe that lectin-containing foods promote inflammation, lead to weight gain, and are toxic to the body. However, there’s very little research on lectin’s effects on the body. A 2004 review published in Toxicon looked at the limited information regarding lectin and determined that it’s an antinutritive and/or toxic substance. Researchers in Brazil determined that, because lectin survives digestion in the gastrointestinal (GI) tract, it can bind to the cell lining within the digestive tract and lead to a series of harmful local and systemic reactions. However, foods with high amounts of lectin, such as kidney beans, aren’t eaten raw. Once soaked and cooked, the lectin content is significantly reduced and, as such, isn’t a potential issue for the body. Furthermore, the commonly known health benefits of consuming whole grains and pulses, such as reduced inflammation, far outweigh any concern for the small amount of lectin found in these foods.

Although the scientific literature raises theoretical concerns about the potential toxicity of lectin, research also suggests lectin provides health benefits with regard to GI metabolism and cancer prevention. A 2016 article published in Current Protein & Peptide Science reviewed the anticancer activity seen in mushrooms in vitro and in vivo. Researchers concluded that lectin may have a possible role in the treatment of cancer and even could be used in antitumor drugs in the future. A study in 1993 published in the European Journal of Clinical Nutrition discussed the possible benefit of lectin to gut health, specifically due to the fact it isn’t digested and can be transported across the gut wall. The study examined animal trials, however, and research is limited in humans.

Putting Research Into Practice

Given the strong scientific data that support the health benefits of pulses, nuts, fruits, and vegetables (ie, foods in which lectin is found), and the scarce scientific evidence available on the harmful effects of lectin, it would be nonsensical for any dietetics professional to recommend a lectin-free diet. Furthermore, because they provide a wide array of important nutrients, removing lectin-filled foods from the diet, especially over a long period of time, can lead to potential deficiencies. However, as the media and current diet culture continue to have a strong influence on consumer behavior, dietetics professionals should be prepared to answer questions about lectin and debunk the myth surrounding avoidance of lectin-containing foods. As set forth by the 2015–2020 Dietary Guidelines for Americans, RDs should promote a well-balanced, varied diet filled with whole grains, fruits, vegetables, low-fat or nonfat dairy, lean protein, and healthful fats.