A lot of people are eating white bread and white rice, refined low-nutrient foods, while avoiding healthful foods like legumes because they are afraid of the “anti-nutrients” in whole grains, beans, certain types of nuts, etc. This is upsetting because it’s entirely unnecessary to avoid these foods; the notion is an absurdist interpretation of food science and nutrient absorption in the human body.
The compounds classified as anti-nutrients include:
- Glucosinolates in cruciferous vegetables, which can prevent the absorption of iodine
- Lectins in legumes and whole grains, which can interfere with the absorption of calcium, iron, phosphorous, and zinc
- Oxalates in green leafy vegetables, rhubarb, bran cereals, beets, berries, chocolate, and tea, which bind to calcium and prevent absorption
- Phytates in whole grains, seeds, legumes, and some nuts, which can decrease the absorption of iron, zinc, phosphorous, and calcium
- Saponins in legumes and whole grains, which can interfere with the absorption of many nutrients
- Tannins in tea, coffee, red wine, chocolate, unripened fruit, and legumes, which can decrease iron and protein uptake
Many of the anti-nutrients, including phytates, lectins, and glucosinolates, can be removed or deactivated by soaking, sprouting, or boiling the food before eating it.
The glucosinolates in raw cruciferous vegetables such as kale or broccoli are generally not a problem unless you consume enormous amounts of these uncooked vegetables and have bothan underlying thyroid disorder and an iodine deficiency.
According to an informative article from the Harvard T.H. Chan School of Public Health (https://www.hsph.harvard.edu/nutritionsource/anti-nutrients/lectins/), eating raw or undercooked kidney beans is dangerous and can cause nausea, vomiting, stomach upset, diarrhea, bloating and gas. A compound in raw and undercooked kidney beans, phytohaemagglutinin, causes red blood cells to lump together. Lectins can bind to cells in the lining of the gastrointestinal tract and disrupt the breakdown of absorption of minerals. Because lectin proteins bind to cells for an extended period, they can potentially cause an autoimmune response, and hypothetically could play a role in inflammatory diseases such as rheumatoid arthritis and type 1 diabetes. That’s fine because how many of you have ever sat down to a beautiful bowl of uncooked kidney beans? I’m going to go out on a limb here and guess none. Luckily, lectins are destroyed by cooking, especially boiling or stewing, or soaking in water for several hours. Dried beans are generally soaked for several hours and then boiled for several hours. Beans prepared this way, or canned beans, are essentially lectin-free.
Similarly, the oxalates in food aren’t much of a concern as long as these foods aren’t your only source of calcium. If you drink a glass of milk or eat a container of yogurt, you’ll more than makeup for the amount of calcium that you didn’t absorb from your spinach salad.
Some people are soaking their whole grains, such as wheat, corn, barley, rice, and oats to remove the phytic acid before eating them. Phytic acid is only in the hull or bran of a grain; so, for example, white rice contains no phytic acid. Deficiency from eating phytic-acid containing foods is unlikely to occur in any developed nation. People in developing countries who subsist mainly on rice have some reason for concern. If you eat dairy products, meat, and seafood, or certain vegetables including kale and bok choy, there isn’t much risk of the small amounts of phytic acid in your whole grains causing you to become mineral deficient. If you consume animal protein, onions, or garlic with your phytate-rich whole grains, nuts, or seeds, the zinc absorption from the phytate-rich food will be enhanced. Phytate’s effect on plant-based iron absorption also varies by the specific type of food chosen; for instance, the iron in pea protein is absorbed much more readily than the iron in soy protein. Vitamin C rich foods such as tomatoes or oranges also increase the absorption of iron.
Some experts recommend avoiding the practice of eating large amounts of foods containing anti-nutrients in one sitting. Individuals with specific deficiencies, such as osteoporosis or iron-deficiency anemia might want to pay some attention to their food choices and to alter the timing of eating foods with anti-nutrients; for example, maybe eating salad and yogurt at different meals if you’re trying to maximize calcium absorption. It is possible that people with an underlying digestive problem, such as irritable bowel syndrome, would be more likely to have reactions to foods that contain anti-nutrients.
However, vegetarians, who consume a diet very high in anti-nutrients, are not often deficient in iron and zinc. It is hypothesized that the vegetarian body adapts to the presence of anti-nutrients by increasing absorption of the minerals in the intestines. Also, remember that foods, including onions and garlic, have been shown to increase the bioaccessibility of both iron and zinc, and vitamin C rich foods increase the absorption of iron.
Phytates have been found to lower cholesterol, slow digestion, and prevent sharp rises in blood sugar, as well as prevent osteoporosis. Lectins similarly slow down digestion and the absorption of carbohydrates, therefore preventing sharp increases in levels of blood glucose and insulin. Many anti-nutrients have also been proven to have antioxidant and anticancer actions. Lectins are being studied for their ability to cause cancer cell death. Researchers are also investigating if non-toxic, low amounts of lectins might help to stimulate gut cell growth in patients who are unable to eat food for an extended period. Lectin-containing foods, including beans, peas, nuts, and whole grains are associated with decreased risk of heart disease, type 2 diabetes, and overweight. The same foods that contain the “anti-nutrients” are rich sources of many nutrients, including potassium, magnesium, fiber, vitamin C, vitamin A, and many more. Fiber itself prevents the absorption of some nutrients, but no one would ever say that we should eat a fiber-free diet.