A Primer on Anti-Nutritional Factors

An anti-nutritional factor is any component of a food that is detrimental to health, to a limited degree. An anti-nutritional factor is not poisonous, although in high quantity, some anti-nutritional factors can cause grave harm. These factors, especially the ones that are not particularly harmful, are found in many ordinary foods that people eat every day. But it is useful to be aware of these factors, so that, when we are choosing which foods to store or to grow, we can make an informed decision. More on anti-nutritional factors.


This anti-nutritional factor is called ‘tannin’ because it is a tan or brown color. Tannins bind to protein, preventing some of the protein from being absorbed by the body. Tannins can also bind to starch (complex carbs). Many grains and beans have tannins, but the lighter the color of the grain or bean, the less tannins it has. Darker grains might seem healthier, but in reality, the lighter grains have less tannins. More on tannins.

Oxalic acid

Oxalic acid is found in foods such as spinach, amaranth, chives, parsley, cassava, radishes, garlic, and Brussels sprouts. Oxalic acid reacts to form calcium oxalate. This can remove calcium from the diet, reducing the intake of that nutrient. In large enough amounts, calcium oxalate can also contribute to kidney stones, harm kidney functioning, cause pain in joints, and other health problems. Livestock that consume high oxalic acid forage will not thrive and may die. More on oxalic acid.

Protease Inhibitors

This class of enzymes inhibits an enzyme used in human digestion of protein, thereby reducing the absorption of protein. Foods containing protease inhibitors include soybeans and lima beans. While beans are a good supplementary source of protein, vitamins, and minerals, they are not suitable as a main staple food, due to excessive anti-nutritional factors.

Phytic Acid

While tannins and protease inhibitors reduce the absorption of protein, phytic acid reduces the absorption of minerals. Foods high in phytic acid include wheat bran, corn, peanuts, and soybeans. More on phytic acid.


This anti-nutritional factor has benefits as well as detriments. It is found in cruciform vegetables, like cabbage, broccoli, cauliflower, and Brussels sprouts. The molecule is related to glucose and an amino acid. Some studies show a decreased risk of cancer from cruciform vegetables in the diet. However, glucosinolates also bind to iodine, reducing its uptake from the diet. A deficiency in iodine can result in goiters. More on glucosinolates.


Oligosaccharides are a form of carbohydrate with 3 to 10 sugar molecules linked together. Shorter carbs are called sugar, and longer carbs are called starch. Bacteria in the intestinal tract will digest oligosaccharides, causing gas and intestinal distress in many persons. Foods high in oligosaccharides includes beans, leeks, Jerusalem artichoke and yacon. To remove most of the oligosaccharides in beans, try this hot soak method.


Dietary fiber is necessary for good health. However, excess fiber intake results in decreased nutrition. Too much fiber in the diet makes all of the nutrients in food less available for absorption: less protein, carbs, fat, vitamins and minerals. If you are eating an unhealthy Western-type diet, you probably get too little fiber. The Institute of Medicine recommends 25 to 38 grams of fiber per day for adults. But if you are eating a diet heavy in foods you grew yourself in a large garden or small mini-farm, you might have too much fiber in the diet. There is something to be said for refined grains and other refined foods, that are low in fiber. Too much fiber is a nutritional disadvantage.

Reducing Anti-nutritional Factors

You can reduce the anti-nutritional factors in your diet by choosing to eat less of those foods that are high in anti-nutritional factors. Choose light colored grains and legumes. Avoid eating foods high in oxalic acid. Cruciform vegetables are healthy in moderate amounts, but be sure to have some iodine in your diet (perhaps from iodized salt), and don’t eat cruciform vegetable at every meal. In addition, many anti-nutritional factors can be reduced by boiling the food and discarding the water. Steaming food can also be effective in reducing anti-nutritional factors. Cooking foods in various ways (baking, boiling, steaming) will deactivate protease inhibitors, but boiling is more effective at removing more anti-nutritional factors.

– Thoreau

2 Responses to A Primer on Anti-Nutritional Factors

  1. So… I shouldn’t eat any: spinach, amaranth, chives, parsley, cassava, radishes, garlic, and Brussels sprouts, soybeans and lima beans, wheat bran, corn, peanuts, cabbage, broccoli, cauliflower, and Brussels sprouts, beans, leeks, Jerusalem artichoke and yacon (what’s a yacon?). So what’s left? Show me the bodies of the people who ate these things because I suspect this is pure BS.

    • You can eat all of those foods in moderation. But we should be aware of the nutritional content of the foods we choose, as well as any anti-nutritional factors. Search on Google scholar; there are plenty of scientific studies on anti-nutritional factors.