Lectins, a type of protein found in many plant foods, can cause damage to the lining of your gastrointestinal tract or your organs and interfere with metabolism when consumed in large amounts, according to a study published in "Toxicon" in September 2004. However, they may also have some health benefits. For example, a review article published in "Critical Reviews in Food Science and Nutrition" in 2005 noted that lectins may have some anti-cancer potential via changes to the immune system and minimizing the growth of tumors, although research is still in the preliminary stages.
Beans and Pulses
Beans are among the main sources of lectins. Soy, kidney, navy, pinto, lima, fava, wax, castor, jack, string and field beans all contain lectins. Sweet peas, green peas, cow peas and horse grams are other sources of these proteins, as are lentil, mung bean or soybean sprouts. Fully cook your beans before eating them. Cooking and digestion destroy some, but not all, lectins. For example, the lectins in navy beans aren't fully destroyed during digestion.
Grains and Cereals
Barley, corn, rice and wheat, especially wheat germ, also contain lectins, as do cereals and other baked goods made with these grains. Wheat germ contains one of the types of lectin that isn't destroyed during digestion.
Fruits and Vegetables
Tomatoes contain lectin, and so do potatoes, sweet potatoes, zucchini, carrots, rhubarb, beets, mushrooms, asparagus, turnips, cucumbers, pumpkin, sweet peppers and radishes. Citrus fruits, such as oranges, lemons and grapefruit, provide lectin. So do berries, including blackberries, raspberries and strawberries. Other fruit sources of lectin include pomegranate, grapes, cherries, quinces, apples, watermelon, banana, papaya, plums and currants.
You'll also be consuming lectin if you eat nuts and seeds, even those that have been dry roasted. Walnuts, hazelnuts, peanuts, sunflower seeds, sesame seeds and coconut all contain lectins. Chocolate, coffee and some spices, including caraway, nutmeg, peppermint, marjoram and garlic, are also sources of lectins.