What is food ?

Food makes your body work, grow and repair itself. The kind of food you eat can affect the efficiency of these processes. Body function and the food that sustains it is infinitely complex. Food is in fact one of the most complicated sets of chemicals imaginable.

Getting to know which nutrients are in which foods can help you to understand something of this complex relationship between your food and your body.

Chemicals in food

Food is composed of many different chemical substances - 'macronutrients' (major nutritional components that are present in relatively large amounts, such as protein), 'micronutrients' (major nutritional components that are present in relatively small amounts, such as vitamins), water, and roughage (dietary fibre). Many other components can also be present in food

Food may contain colours (natural and synthetic), flavours, pharmacologically active substances (such as caffeine, steroids, and salicylates, which chemically affect the body), natural toxicants (naturally occurring poisons, such as cyanide),  and various contaminants (substances resulting from a contaminated environment, such as pesticides). Even characteristic flavours such as those of oranges and passionfruit can depend on the presence of a dozen or more chemicals.

The chemical nature of food is changed by storage, preservation and, especially, by cooking. Food chemicals can also interact amongst themselves within the body. For example, the availability to the body of iron from plant sources depends on the amount of vitamin C present in the food eaten. The way in which carbohydrate is absorbed from the bowel depends to some extent on the presence of dietary fibre, even though the fibre itself is not absorbed.

Physical form of food

Food is also more than just the chemicals it contains. Its physical characteristics are important. The size of food particles can affect the extent to which nutrients are digested and made ready for by the body. For example, eating an intact apple has nutritional value different from drinking all the same chemicals in an apple purée. Ground rice is more rapidly digested than unground rice. Nutrients can be more easily absorbed from peanut butter (paste) than from peanuts eaten whole.

Acid or alkaline

The acidity and alkalinity of food are physical properties often thought to be important. In fact, they are only important insofar as they might alter the rate of emptying of the stomach, digestion in the small bowel and the acidity or alkalinity of the urine. Our bodies can cope with a wide range in and alkalinity without much problem. Acid foods are generally sour while alkaline foods often have a slightly soapy taste. The use of sodium bicarbonate (baking soda) can make foods alkaline. It can also cause loss of vitamin C and contribute to our intake of sodium.

http://apjcn.nhri.org.tw/server/info/books-phds/books/foodfacts/html/maintext/main2a.html