While whole grains and vegetables are nutritious, some of them also contain substances that decrease the absorption of minerals. These substances, called “antinutritional factors”, or antinutrients, include phytate, oxalate, and trypsin inhibitor. While not technically antinutrients, fibre and polyphenols can also reduce the availability of nutrients in the diet.
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Antinutrients – What Are They?
Antinutrients are toxins naturally found in foods that interfere with how our bodies absorb or use nutrients. Antinutrients are often found in plants because they benefit the plants in some way – for example, keeping pests from eating the plant while it grows.
Wheat Bran and Grains Contain Phytate (Phytic Acid)
Phytate is found in wheat bran, unleavened (yeast-free) bread, whole grains, legumes, and nuts. It binds to some minerals (especially zinc and iron), which stops them from being usable by the body. The only people who have problems because of phytates are those who rely heavily on unleavened bread.
Leafy Green Vegetables Contain Oxalate (Oxalic Acid)
Oxalate is a compound found in leafy green vegetables and whole grain foods. It prevents the body from absorbing some of the calcium and other minerals in these foods. Oxalate is highest in wheat bran, rhubarb, spinach, chard and beet greens. People relying on plant sources of calcium should choose a variety of vegan calcium-rich foods.
Soybeans Contain Trypsin Inhibitors
Raw soybeans contain high amounts of trypsin inhibitor. Trypsin inhibitor lowers the ability of the body to digest protein. To stop the action of trypsin inhibitor, soybeans can be cooked, sprouted or fermented. Soy foods like edamame (young immature soybeans), cooked whole soybeans, tempeh and tofu are good choices.
All Plant Foods Contain Fibre
Fibre (roughage) can limit the absorption of zinc, iron and calcium from food. But eating large quantities of fibre is not known to cause problems in people eating a balanced diet, vegetarian or not.
Spices, Tea, Coffee and Red Wine Contain Polyphenols
Polyphenols are healthful compounds found in a variety of vegetables, spices, and beverages. But because they can decrease the absorption of iron, it’s recommended to avoid drinking coffee or tea with meals.
Vegetarian Diets Also Contain Nutrient Enhancers
While antinutrients decrease the amount of minerals available from food, vegetarian diets also contain substances that allow the body to absorb more nutrients. For example, eating vitamin C with iron-rich plant foods increases iron absorption. So eating a tomato or a green pepper with a spinach salad will increase the amount of iron absorbed compared to eating just spinach.
Some vegetarian foods may be high in antinutrients, but it is still possible to get the required minerals with a balanced vegan or vegetarian diet.