Lectins are proteins that bind carbohydrates. There are many different kinds, which have different functions because they bind to different carbohydrates. Lectins are not only present in plant foods; they are ubiquitous in nature – in plants, animals, and microorganisms.
The main function of lectins in animals is to facilitate cell to cell contact – lectins on one cell recognize and bind to surface carbohydrates on another cell. In plants, the function is less clear, but some are thought to be plant defense proteins, to protect against pathogens and insects. This is similar to other phytochemicals. Flavonoids, for example, also serve as natural defenses in plants.
Plant lectins bind carbohydrates during digestion, slowing or preventing their breakdown, and thereby reducing the glycemic effects of the food. You may hear a claim that lectins “disrupt digestion,” but this is misleading. This action of lectins is most likely a contributing factor to the pro-weight loss and anti-diabetes effects of beans and other plant foods. Beans are rich in anti-cancer phytochemicals and are the foods demonstrating the most powerful association with lower rates of breast cancer in massive epidemiological studies.
A lectin in common mushrooms has been found to inhibit proliferation of cancer cells in vitro. Mushrooms are another food offering powerful protection against cancer. And that’s not the only one: similar results have been found for lectins from fava beans, soybeans, bananas, buckwheat, jackfruit, and wheat. Some of these lectins are being investigated as potential cancer therapies. Certain plant food lectins may also help prevent cancer development by blocking the actions of angiogenesis-promoting lectins on human cells.
Do lectins pose any dangers?
There is one lectin known to cause temporary gastrointestinal distress in humans, however it is easily avoided. A lectin called phytohemagglutinin found in raw beans (red kidney beans in particular) binds to a carbohydrate present on human intestinal cells. It is inactivated by cooking. If you use dry beans, take the necessary precaution of making sure they are thoroughly cooked – don’t eat undercooked beans.
Special cases of sensitivity to certain lectins
Some food allergies are allergies to a lectin specific to that food. Also, bacterial infections, inflammatory bowel disease (IBD), colon cancer, or autoimmune illnesses may alter intestinal cells in a way that makes usually harmless food lectins problematic. For example, wheat may be problematic for rheumatoid arthritis and peanuts for IBD and colon cancer. However, carbohydrates from dietary fiber could potentially block or reduce these harms. It is likely there are individuals who should avoid a specific food because of their individual response to a lectin in that food. But this does not mean that lectins are harmful for the general population. In fact, foods having more lectins are longevity promoting.
Keep eating beans and tomatoes – they have huge health benefits
People who regularly eat beans have greater intakes of minerals and fiber, have lower blood pressure, and are less likely to be overweight than people that don’t consume beans. The consumption of beans is linked to lifespan enhancement, lower rates of cardiovascular disease, lower risk of colorectal and several other cancers. Beans are a high-fiber, high-resistant starch, low-glycemic source of calories. The high total and soluble fiber content of beans helps to lower cholesterol and blood pressure. Fiber and resistant starch fuel the growth of a healthy gut microbiome, which likely underlies beans’ ability to protect against colorectal cancers.
Tomatoes are the major source of the carotenoid lycopene, a strong antioxidant that helps protect the skin from UV damage. In addition, tomatoes have a number of cardiovascular system benefits including making LDL cholesterol more resistant to oxidation. Higher blood lycopene is associated with a lower risk of heart attack and stroke, and low blood lycopene are associated with a greater risk of premature death.
Beans, vegetables, mushrooms, nuts and seeds are high-nutrient, fiber-rich foods that are consistently associated with beneficial health outcomes and a longer life; this suggests that if there is any potential negative of certain plant lectins, it is enormously outweighed by the benefits of the fiber and phytochemicals in these plant foods.
Source: Joel Fuhrman, MD