Ask the RD
QUESTION: What are lectins, and why are people saying they are so harmful to health? Should I really give up eating beans?
ANSWER: Lectins are proteins in whole grains, some vegetables and legumes, including beans. They are among many plant substances that can inhibit nutrient absorption. Tannins, phytic acid and even beneficial fiber are also considered “anti-nutrients.” Lectins can bind to carbohydrates, which can harm the gut and produce all kinds of health problems, according to the current popular rhetoric. After gluten, lectins seem to be the new thing to avoid.
Actually, lectins are being studied for their potential roles in treating digestive cancers (Estrada-Martinez et al. 2017). They are known to exhibit antimicrobial, insecticidal and antitumor activity (Lagarda- Diaz, Guzman-Partida & Vazquez-Moreno 2017).
It’s true that lectins in raw beans can make you sick with foodborne-illness-type symptoms. I don’t know about you, but the last time I ate raw beans was when my sister dared me to when I was 5. We cook beans and whole grains—and cooking deactivates lectins (Fehily 2016). Soaking, sprouting or fermenting legumes (think: tofu, miso, tempeh and mung bean sprouts) also reduces lectins.
Legumes, whole grains and other nutritious plant foods are responsible for the myriad health benefits of plant-based diets. Beans and other legumes are rich in important nutrients like protein, iron, zinc, potassium and folate, as well as soluble and insoluble fibers (Messina 2014). The Dietary Guidelines for Americans recommends we eat more of them, not less (HHS & USDA). Any time you hear about a popular diet eliminating foods that scientific evidence has shown to be healthful, in this case legumes and whole grains, my advice is to be skeptical and look at the big picture of healthful dietary patterns.
Estrada-Martinez, L.E., et al. 2017. Plant lectins as medical tools against digestive system cancers. International Journal of Molecular Sciences, 18 (7), E1403.
Fehily, A.M. 2016. Nutrition: Soy-based foods. Reference Module in Food Sciences, 2, 348–54.
HHS & USDA (U.S. Department of Health and Human Services & U.S. Department of Agriculture). 2015–2020 Dietary Guidelines for Americans, 8th edition Accessed July 15, 2018: health.gov/dietaryguidelines/2015/guidelines/chapter-1/a-closer-look-inside-healthy-eating-patterns/#food-groups.
Lagarda-Diaz, I., Guzman-Partida, A.M., & Vazquez-Moreno, L. 2017. Legume lectins: Proteins with diverse applications. International Journal of Molecular Sciences, 18 (6), E1242.
Messina, V., 2014. Nutritional and health benefits of dried beans. American Journal of Clinical Nutrition, 100 (1, Suppl.), 437S–42S.