The composition of a given food does not necessarily make it an effective nutrient. A lot of common foods in their natural state contain substances (antitrypsic factors) that inhibit or even prevent the assimilation of certain fundamental nutrients. Because of their negative effect on nutrition, these foods have come to be called natural anti-nutrients. Here are a few examples:
– Although egg whites contain a lot of excellent quality proteins, those proteins are all but indigestible in the raw state. The substance that prevents their assimilation is destroyed by cooking, which means you should always eat your eggs cooked, with the white part fairly firm.
– Untreated milk contains the same substances. Since they are destroyed by pasteurization and/or fermentation, most people don’t have a problem digesting milk products. An exception is fresh cheese made from non-pasteurized milk.
– A number of protein-rich vegetables (soybean, beans, lentils, grains) have the same problem when eaten raw. Fortunately their antitrypsic factor is destroyed by cooking, fermentation and, at least partially, by sprouting.
There are also substances capable of destroying vitamins in some foods, or in the intestines, while the food is being digested. Fish sometimes contains thiamin, which destroys Vitamin B1, but which itself is destroyed by heat. Corn contains a substance that destroys Vitamin PP, but which is itself destroyed by fermentation but not in the preparation of other corn-based products like polenta.
Some foods contain anti-hormones that cause hormonal problems in people or animals who consume them. For example, animals who eat large amounts of rutabaga or cabbage can develop goitre because of an adverse effect on the thyroid gland.