Should you be eating anti-nutrients?

By Melissa Sammy, MDLinx
Published August 8, 2019

Key Takeaways

When we think about food nutrition, we tend to only consider a handful of factors, such as calories, carbs, protein, sugar, vitamins, and minerals. But what about the substances that aren’t usually reflected on food labels—like anti-nutrients?

Anti-nutrients are natural compounds often found in foods generally considered healthy— whole grains, legumes, nuts, seeds, fruits, and vegetables—the very same foods we’ve been encouraged to eat as part of a healthful, balanced diet.

But, with a prefix like “anti–,” they must be bad for your health, right? Well, yes…and no. It’s a bit more complicated than that, actually.

Let’s take a closer look at what anti-nutrients are, foods that contain them, and the different effects they can have on your health.

What are anti-nutrients?

Anti-nutrients are exactly what they sound like. Where nutrients are substances that provide our bodies with nourishment integral to growth and survival, anti-nutrients are the opposite: substances that block the absorption of nutrients into the body. Essentially, anti-nutrients decrease the nutritive value of food.

Some experts theorize that anti-nutrients exist in plants to protect them against insects, animals, and other predators that would otherwise consume them in large quantities. For instance, some plants of the nightshade family (Solanaceae)—including belladonna, eggplant, potatoes, tomatoes, and peppers—contain the anti-nutrient alkaloids solanine and chaconine, which can be poisonous when consumed in high concentrations.

Potato leaves, stems, and shoots, in particular, are naturally high in both solanine and chaconine, and when potato tubers are exposed to light, they turn green and increase their production of these anti-nutrients. In itself, the green color from the chlorophyll production is harmless, but it serves as an indication that high levels of solanine and chaconine may be present to ward off predators. Symptoms of toxicity can include nausea, diarrhea, vomiting, stomach cramps, burning of the throat, headache, and dizziness. Of note, US adults consume about 65 kg of potatoes annually, and consumption of potatoes high in solanine and chaconine has been associated with numerous poisonings and some fatalities.

Should you avoid them?

Although anti-nutrients can prevent your body from absorbing key nutrients like calcium, iron, and zinc, they typically aren’t a major concern for the average person with a healthy diet. That’s because most of these anti-nutrients are either reduced or deactivated during the cooking process.

Soaking, boiling, sprouting, and/or fermenting foods rich in phytates, lectins, and glucosinolates, for example, can increase their nutritional value while attenuating any potential adverse health effects. And you may already be in the habit of doing this without being aware of the underlying reason. For instance, people often soak legumes, such as lentils, overnight before cooking. In addition to hastening the cooking process, soaking legumes beforehand has the added benefit of reducing phytic acid, protease inhibitors, lectins, and tannins.

On a related note, cooking, frying, or microwaving potatoes will have a negligible effect in reducing their solanine and chaconine contents. However, glycoalkaloid toxicity from potatoes can be minimized by peeling and boiling them before consumption.

Moreover, it’s important to note that, when carefully processed and consumed in small amounts, some anti-nutrients may offer certain health benefits. Dietary fiber, for example, can block the absorption of carbs, which can be beneficial in controlling diabetes. Tannin-rich foods may have favorable cardiovascular and anti-cancer properties due to their antioxidant activity. In addition, lectins may have therapeutic value in combating tumor growth and cancer, according to some research.

Some of the more widely researched anti-nutrients include the following:

Glucosinolates: Cruciferous vegetables—such as broccoli, Brussels sprouts, and cabbage—are rich in glucosinolates. They can interfere with the production of thyroid hormone, primarily by disrupting your thyroid’s use of iodine, thus increasing your risk for developing goiters. Individuals with iodine deficiency or hypothyroidism are at the highest risk.

Lectins: This family of proteins is often found in legumes (eg, lentils, peanuts, and soybeans) and whole grains. They can inhibit the absorption of calcium, iron, phosphorus, and zinc. Furthermore, because lectins bind directly to the lining of the small intestines, they can cause lesions in the intestines, which may contribute to leaky gut syndrome. Lectin consumption has also been associated with an increased risk of heart disease and autoimmune diseases, such as lupus and rheumatoid arthritis.

Saponins: Like lectins, saponins can be found in some legumes—namely soybeans, chickpeas, and quinoa—and whole grains, and can hinder normal nutrient absorption. Saponins can disrupt epithelial function in a manner similar to lectins, and cause gastrointestinal issues, like leaky gut syndrome.

Oxalates: Often found in green leafy vegetables—particularly members of the spinach family—and tea, oxalates bind to calcium and block it from absorption. Consumed frequently and in excess, oxalates can crystalize in tissues and increase the risk of kidney stones. Thus, if you’re prone to calcium oxalate stones or at risk for osteoporosis, you may want to consider a low-oxalate or oxalate-controlled diet.

Phytates(phytic acid): Abundant in the hulls of nuts, seeds, and grains, phytic acid has a strong binding affinity for calcium, magnesium, iron, copper, and zinc, which can prevent their absorption. Of note, diets rich in phytates can contribute to zinc deficiency, which can impair the immune system and cause hair loss, impotence, and eye and skin lesions. However, they can also lower your cholesterol, slow digestion, and prevent steep spikes in serum glucose levels.

Tannins: This class of antioxidant polyphenols—most often found in tea, coffee, chocolate, grapes, berries, and legumes—is responsible for the astringent taste we experience when we drink wine or eat unripe fruits. Tannins inhibit trypsin, chemotrypsin, amylase, and lipase activity, and decrease the protein quality of foods. They can also impair iron digestion and lead to iron deficiency anemia. In some animal studies, tannins have also been shown to cause decreased growth and protein digestibility.

Fiber: Yes, fiber is an anti-nutrient. Fiber decreases the absorption of carbohydrates, thus reducing blood glucose and insulin levels as well.

In the grand scheme of things, plant-based foods that house these anti-nutrients—fruits and leafy green vegetables—have been shown time and again to exert an overall positive effect on health. Thus, the pros of healthy foods that contain anti-nutrients far outweigh the cons. While it’s unrealistic to eliminate these foods from our diets, we can control how much of these foods we eat, as well as how we process and cook them.

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