Food Components

Food components

The three major components of food, known as macronutrients, are proteins, fats, and carbohydrates.

Proteins are chemical chains of various combinations of 20 naturally-occurring amino acids. Muscle tissue consists mainly of proteins. The body breaks up dietary proteins into amino acids that are used for tissue repair, to produce many of the hormones and enzymes that regulate metabolism, and as a source of energy. The chemical processes of the body require nine of these "essential" amino acids in the diet. Other amino acids may be synthesized from these nine. Unlike animal proteins, plant proteins may not contain all the essential amino acids in the necessary proportions for good health. Vegetarian diets must contain the right balance of grains and legumes to prevent dietary deficiency diseases.

Fats belong to the group of chemicals called lipids which are insoluble in water but soluble in organic solvents. Fats are important structural constituents of cells and they are precursors for many substances in the body. Fats are also metabolized as a source of energy. Cell membrane behavior and cell signaling in all tissues of the body are highly dependent on the lipid constituents of cells. Over half of the weight of the brain consists of lipid components. Triglycerides are the major component of food fats. Triglycerides consist of one glycerol molecule and three fatty acids typically containing 12 to 22 carbon atoms. They are classified as saturated, monounsaturated and polyunsaturated based on the amount of hydrogen in the chemical structure of the component fatty acids.

Each point of unsaturation, indicated by a double bond between carbons, can have a Cis or a Trans configuration which affects the shape of the molecule and its biochemical properties. A saturated fat does not have double bonds and cannot accept any additional hydrogen atoms. In general, unsaturated fats are liquid and saturated fats are solid. Most vegetable oils have a higher proportion of unsaturated to saturated fats than animal fats. Some unsaturated fats, called "essential fatty acids" (EFA), are necessary for the development and maintenance of the brain and eyes. Hydrogenation is a commercial chemical process to add more hydrogen to natural unsaturated fats to make them solid. Partial hydrogenation has the side-effect of transforming a portion of the natural Cis fatty acids to Trans fatty acids which can have harmful health effects.

Carbohydrates are simple sugars or polymers of simple sugars called polysaccharides or complex carbohydrates. Dietary carbohydrates are metabolized to provide energy and increase the reserves of fat in the body. No dietary carbohydrates have been determined to be "essential" for human nutrition, although cartilage and some secretions have carbohydrate polysaccharide components, and it is known that sugars help proteins fold properly and remain stable. Carbohydrates, like the starch in potatoes, are easily digestible and rapidly increase the sugar level in the body. Complex carbohydrates like those in whole grains are digested more slowly. Cellulose, which is a polymer of glucose, cannot be digested by humans. The Glycemic Index of a food is a measure of how fast the food increases the blood sugar level compared to a dose of glucose.

Trace nutrients or micronutrients consist of phytochemicals, vitamins and minerals which are necessary for many functions of the body at the molecular level. Micronutrients are found in a variety of foods. For example, liver and red meats are good sources of iron. Seafood provides more iodine and copper than meats from land-based animals. Green vegetables are a good source of magnesium and antioxidants. Milk is a good source of calcium and phosphorus. Bananas are rich in potassium.

Non-digestible components such as fiber and cellulose are not nutrients, but they create bulk that helps to clean the intestines and moderate the absorption of nutrients. A portion of the ingested fiber is fermented by microflora in the intestines and converted into short-chain fatty acids that can be metabolized. Refined foods have a lower content of fiber than whole foods. White wheat flour, for example, has less fiber than whole wheat flour because the outer shell of the wheat grains is discarded in making the white flour.