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Phytic acid (deprotonated phytate anion in the picture) is an antinutrient that interferes with the absorption of minerals from the diet.

Antinutrients are natural or synthetic compounds that interfere with the absorption of nutrients.^[1] Nutrition studies focus on these antinutrients commonly found in food sources and beverages.

Examples

Phytic acid 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.^[2][3] Phytic acids are common in the hulls of nuts, seeds and grains and of great importance in agriculture animal nutrition and eutrophication wise due to the mineral chelation and bound phosphates released in to the environment. Without the need to use phytate (but also nutrient) reducing milling,^[4] the amount of phytic acid is commonly reduced in animal feeds by adding histidine acid phosphate type of phytases to them.^[5]

Protease inhibitors are substances that inhibit the actions of trypsin, pepsin and other proteases in the gut, preventing the digestion and subsequent absorption of protein. For example, Bowman–Birk trypsin inhibitor is found in soybeans.^[6]

Lipase inhibitors interfere with enzymes, such as human pancreatic lipase, that catalyze the hydrolysis of some lipids, including fats. For example, the anti-obesity drug orlistat causes a percentage of fat to pass through the digestive tract undigested.^[7]

Amylase inhibitors prevent the action of enzymes that break the glycosidic bonds of starches and other complex carbohydrates, preventing the release of simple sugars and absorption by the body. Amylase inhibitors, like lipase inhibitors, have been used as a diet aid and obesity treatment. Amylase inhibitors are present in many types of beans; commercially available amylase inhibitors are extracted from white kidney beans.^[8]

Oxalic acid and oxalates are present in many plants and in significant amounts particularly in rhubarb, tea, spinach, parsley and purslane. Oxalates bind to calcium and prevent its absorption in the human body.^[9]

Glucosinolates prevent the uptake of iodine, affecting the function of the thyroid and thus are considered goitrogens. They are found in plants such as broccoli, brussel sprouts, cabbage, mustard greens, radishes and cauliflower.^[10]

Excessive intake of required nutrients can also result in them having an anti-nutrient action. Excessive intake of dietary fiber can reduce the transit time through the intestines to such a degree that other nutrients cannot be absorbed. However, this effect is often not seen in practice and reduction of absorbed minerals can be attributed mainly to the phytic acids in fibrous food.^[11][12] Foods high in calcium eaten simultaneously with foods containing iron can decrease the absorption of iron via an unclear mechanism involving iron transport protein hDMT1, which calcium can inhibit.^[13]

Some proteins can also be antinutrients, such as the trypsin inhibitors and lectins found in legumes. These enzyme inhibitors interfere with digestion.^[14]Avidin is an antinutrient found in active form in raw egg whites. It binds very tightly to biotin (vitamin B7)^[15] and can cause deficiency of B7 in animals^[16] and, in extreme cases, in humans.^[17]

Widespread form of antinutrients are the flavonoids, which are a group of polyphenolic compounds that include tannins.^[18] These compounds chelate metals such as iron and zinc and reduce the absorption of these nutrients,^[19] but they also inhibit digestive enzymes and may also precipitate proteins.^[20]

Saponins in plants may serve as anti-feedants^[21][22] and can be classified as antinutrients.^[23]

Occurrence

Antinutrients are found at some level in almost all foods for a variety of reasons. However, their levels are reduced in modern crops, probably as an outcome of the process of domestication.^[24] The possibility now exists to eliminate antinutrients entirely using genetic engineering; but, since these compounds may also have beneficial effects, such genetic modifications could make the foods more nutritious but not improve people's health.^[25]

Many traditional methods of food preparation such as fermentation, cooking, and malting increase the nutritive quality of plant foods through reducing certain antinutrients such as phytic acid, polyphenols, and oxalic acid.^[26] Such processing methods are widely used in societies where cereals and legumes form a major part of the diet.^[27][28] An important example of such processing is the fermentation of cassava to produce cassava flour: this fermentation reduces the levels of both toxins and antinutrients in the tuber.^[29]

See also

• Antimetabolite


• Biopesticide


• Plant defense against herbivory

References

Further reading

• 
  Shahidi, Fereidoon (1997). Antinutrients and phytochemicals in food. Columbus, OH: American Chemical Society. ISBN 0-8412-3498-1.