Antinutrients are chemicals which have been developed by plants for their own defence, among other
biological functions and reduce the maximum absorption of nutrients mainly proteins, vitamins, and
minerals, thus preventing optimal exploitation of the nutrients present in a food and reducing the nutritive
value. Some of these plant chemicals are harmful to health or evidently advantageous to
human and animal health if consumed at suitable amounts. They are present in almost all foods.
Many antinutrients are present in grains, legumes, beans, nuts etc.
Antinutrients in foods
1) Tannins
Tannins are heat stable and they reduce protein digestibility in humans, likely by either making protein
partially unavailable or inhibiting digestive enzymes and increasing fecal nitrogen. Tannins present in food
products and to inhibit the activities of trypsin, chemotrypsin, amylase and lipase, decrease the protein
quality of foods and interfere with dietary iron absorption.
2) Phytate
Phytates has a strong binding affinity to minerals such as calcium, magnesium, iron, copper and zinc.
This results in precipitation, making the minerals unavailable for absorption in the intestines. Phytic acids
are common in the nuts, seeds and grains.
3) Oxalates
A salt formed from oxalic acid is known as an oxalate. These are present in many plants, particularly in
members of the spinach family and soybeans. Oxalates bind to calcium and prevent its absorption in the
human body. If you consume food with excessive amounts of oxalic acid regularly, nutritional deficiencies
are likely to occur, as well as severe irritation to the lining of the gut. The insoluble calcium oxalate has the
tendency to solidify in the Kidneys or in the Urinary tract, thus forming sharp-edged calcium oxalate
crystals when the levels are high enough. These crystals play a role to the formation of kidney stones
formation in the urinary tract when the acid is excreted in the urine.
4) Saponins
Saponins are toxic because they appear to be extremely toxic to fish and many of them
possessed strong hemolytic activity. Saponins, in high concentrations, impart a bitter taste and astringency in
dietary plants. The bitter taste of saponin is the major factor that limits its use. In the past, saponins were
identified as antinutrient components, due to their adverse effects such as for growth impairment and
decrease their food intake due to the bitterness and throat-irritating activity of saponins. In addition,
saponins decrease the bioavailability of nutrients and decrease enzyme activity and it affects
protein digestibility by inhibit various digestive enzymes such as trypsin and chymotrypsin.
5) Lectins
Lectins are carbohydrate binding proteins present in most plants, especially seeds like cereals, beans, etc., in
tubers like potatoes and also in animals. Lectins selectively bind carbohydrates and importantly, the
carbohydrate moieties of the glycoproteins that decorate the surface of most animal cells. Dietary lectins act
as protein antigens which bind to surface glycoprotein’s on erythrocytes. They can cause severe intestinal
damage disrupting digestion and causing nutrient deficiencies; they can provoke IgG and IgM antibodies
causing food allergies and other immune responses and they can bind to erythrocytes, simultaneously with
immune factors, causing hem agglutination and anemia.
6) Protease inhibitors
Trypsin inhibitor and chymotrypsin inhibitor are protease inhibitors occurring in raw legume seeds. Trypsin
inhibitors that inhibit the activity of the enzymes trypsin and chymotrypsin in the gut, thus preventing
protein digestion, are in many plant species mainly in different grain legumes. Trypsin inhibitors are a
unique class of proteins found in raw soybeans that inhibit protease enzymes in the digestive tract by
forming indigestible complexes with dietary protein. These complexes are indigestible even in the presence
of high amounts of digestive enzymes. Protease inhibitors reduce trypsin activity.
How to reduce antinutrients in foods?
1) Soaking
Beans and other legumes are often soaked in water overnight to improve their nutritional value. Most of
the antinutrients in these foods are there in the skin. Since many antinutrients are water soluble, they simply
dissolve when soaked. In legumes, soaking decreases phytate, protease inhibitors,
lectins, tannins and calcium oxalates.
2) Sprouting
Sprouting increases the availability of nutrients in seeds, grains and legumes. During sprouting, changes
take place within the seed that lead to the degradation of antinutrients such as phytate and protease
inhibitors.
3) Heating
High heat, mainly when boiling, can degrade antinutrients like lectins, tannins and protease inhibitors.
Calcium oxalate is reduced in boiling green leafy vegetables; steaming and baking are not as effective. In
contrast, phytate is heat resistant and not as easily degraded with boiling. The cooking time depends on the
type of antinutrient.
