The latest fad diet tells you to try to avoid lectin-rich foods and to buy their products that are supposed to block lectins in the foods that you eat. However, scientific studies show that eating the common foods with high-lectin content is associated with living a long life and avoiding diseases such as heart attacks, certain cancers, and diabetes (JAMA Intern Med, 2013;173(13):1230-1238). These foods include:
• legumes (dried beans, peas, lentils, peanuts)
• whole grains (wheat, rice, oats, barley and so forth)
• foods from the nightshade family (eggplant, peppers, potatoes, tomatoes)
• foods from the gourd family (squash, pumpkin, zucchini)
• many other fruits, vegetables and seeds
What are Lectins?
Lectins are a type of protein found in all forms of life, both animals and plants, including most foods. Lectins can bind to sugars on the membranes covering cells in your body or in other foods you eat. In small amounts, they can provide health benefits, but in large amounts, they can reduce your body’s ability to absorb nutrients or can even be highly toxic. An extreme example is the castor oil bean, a source of the lectin, ricin, which is used as a deadly chemical weapon. Fortunately for us, our ancestors figured out (through trial and error) which plants are edible and which are poisonous. They also discovered that some plant parts needed to be cooked to make them edible (such as dried beans, grains and potatoes).
Why Virtually All Plants Contain Lectins
Plants cannot run away from animals, insects or bacteria that try to eat them, so they need some other way to defend themselves. Many plants have evolved with lectins that can damage the intestines of animals and insects that try to eat them and make them sick or kill them. Lectins are found in large amounts in the seeds of plants where they prevent intestinal juices from digesting and damaging the seeds so the seeds can pass through the intestines of birds and other animals, to be dispersed on the land where they can sprout into new plants.
Can Lectins Harm You?
Lectins in uncooked or under-cooked dried beans and grains can bind to the lining of your intestines to cause vomiting, cramping and diarrhea. However, proper cooking destroys or reduces the amount of lectins to prevent this harm. Lectins are absorbed very poorly, but they can enter your bloodstream to turn on your immunity to cause inflammation (Biochem Soc Trans, 1989;17:481–482; Lancet, 1998;352:1831–1832), an overactive immunity that can attack and destroy your own cells, but many other studies show that fruits and vegetables help to decrease inflammation (J Am Diet Assoc, Mar 2009;109(3):414–421). The rest of the many claims that lectins cause cancer, auto-immune diseases and other ailments are at this time unproven and unsubstantiated by adequate research.
Risks of Restricting Lectins
• Trying to avoid high-lectin foods will deprive you of many foods with proven health benefits. People who eat a plant-based diet with whole grains, beans, fruits and vegetables are at reduced risk for heart disease, diabetes, and certain cancers. See my report on Anti-inflammatory and Pro-inflammatory Foods.
• The most popular low-lectin diet recommends eating foods made from white flour instead of whole grains. This is harmful advice since refined carbohydrates cause high blood sugar levels and therefore increase risk for diabetes and heart attacks. North Americans suffer from an epidemic of obesity and diabetes caused by eating a diet with lots of sugar and refined carbohydrates.
• A lectin-avoiding diet will greatly reduce your intake of soluble fiber, an important dietary component for preventing and treating diabetes and heart attacks.
• If you follow the advice of the lectin-avoidance advocates, you will spend a lot of money on their costly supplements, specialty milks, pasture-raised meats and so forth.
Sensible Ways to Reduce Lectins
The same cooking process that reduces the gas-causing tendencies of beans also reduces their lectin content to a safe level. Soak the beans overnight, discard the soaking water and cover the beans with fresh water. Bring to a boil and then cook with the heat kept just under boiling until the beans are soft. Canned beans have been prepared using this process, so they are not high in lectins. Dry heat does not usually destroy lectins. Sprouted beans, grains and other seeds have low lectin counts. Green (immature) beans and peas have low levels of lectins. Standard methods of cooking whole grains in water destroy or reduce the lectins; if they are soft enough to eat, they are usually safe. Fermenting markedly reduces lectins.
The nightshade family has toxic levels of lectins in the green leaves, stems and shoots, but the fruits (tomatoes, eggplants, peppers) are naturally low in lectins and are perfectly safe to eat. White potatoes should be cooked, which reduces their high lectin content to a safe level. If potatoes have green sprouts or a green tinge on the skin, they should be discarded. Sweet potatoes and yams are from a different plant family and are not high in lectins.
• I believe that the recommendation to avoid foods rich in lectins flies in the face of data that shows that people who eat the most fruits, vegetables, whole grains, beans, nuts and other seeds are the healthiest, live the longest, and enjoy reduced incidence of diseases.
• The healthful diet that I recommend is varied, balanced and high in plants. Do not eat unreasonably large amounts of any single food.
• Follow the traditional cooking practices for dried beans and whole grains; our ancestors learned that these foods should not be eaten raw.
• The expensive supplements promoted to reduce your incidence of supposed lectin disease are not supported by adequate research, and I do not recommend using them.