The term “anti-nutrients” suggests what they are. Whereas nutrients are substances that nourish plants and animals to grow and live, anti-nutrients earn their title because they can block the absorption of nutrients.
The compounds or substances which act to reduce nutrient intake, digestion, absorption and utilization and may produce other adverse effects are referred to as antinutrients or antinutritional factors.
Anti-nutrients are naturally found in animals and many plant-based foods. In plants, they are compounds designed to protect from bacterial infections and being eaten by insects.
There are several compounds in the foods we eat classified as anti-nutrients. Examples include:
Glucosinolates in cruciferous vegetables (broccoli, Brussels sprouts, cabbage)—can prevent the absorption of iodine, which may then interfere with thyroid function and cause goiter. Those already with an iodine deficiency or a condition called hypothyroidism are most susceptible.
Lectins in legumes (beans, peanuts, soybeans), whole grains—can interfere with the absorption of calcium, iron, phosphorus, and zinc.
Oxalates in green leafy vegetables, tea—can bind to calcium and prevent it from being absorbed.
Phytates (phytic acid) in whole grains, seeds, legumes, some nuts—can decrease the absorption of iron, zinc, magnesium, and calcium.
Saponins in legumes, whole grains—can interfere with normal nutrient absorption.
Tannins in tea, coffee, legumes—can decrease iron absorption.
It is not known how much nutrient loss occurs in our diets because of anti-nutrients, and the effects vary among individuals based on their metabolism and how the food is cooked and prepared. Many anti-nutrients like phytates, lectins, and glucosinolates can be removed or deactivated by soaking, sprouting, or boiling the food before eating.