Composition of Food

The human body requires food to provide energy (for life processes and growth), repair and maintain cells and tissues. All food comprises macro-nutrients, micro-nutrients, water and fibre. The macro-nutrients are protein, fat and carbohydrates. These macro-nutrients provide energy, measured in terms of calories, to maintain life. Micro-nutrients comprise vitamins, minerals and trace elements. They perform a multitude of cellular functions, which involve the efficient use and disposal of macro-nutrients. Vitamins and minerals are needed on a daily basis and in small amounts. The body also requires fibre (derived from plants) to promote good health and prevent diseases. The food-related definitions below (Wright 2002) may be useful. See Wright, K. (2002). Extend Your Life. Scotland: Geddes & Grosset.

Proteins: the structural components of the body that form the basis of cells, tissues and organs. They are composed of units called amino acids. Through digestion, proteins are broken down into amino acids that are absorbed by the body. The human body could produce 12 of the 20 amino acids while the remaining 8 (known as essential amino acids) are derived from food. Foods containing proteins are from two sources, animals (such as red meat, poultry, fish, milk, cheese, yogurt and eggs) and plants (beans, peas, pulses, whole grains, nuts and seeds). Since proteins form about 10 to 15% of the daily total calorie intake, nutritionists recommend that only a small amount is needed at each meal.

Fats: contain fatty acid molecules that are either saturated (solid) or unsaturated (softer or more liquid). These are vital components of the membrane that surrounds all types of tissue cell and control the passage of substances into and out of the cells. They are stored inside cells as fuel reserves and are broken down when required to release energy. Cholesterol is a form of saturated fat manufactured from saturated fatty acids by the liver. Cholesterol is involved in the production of steroid, hormones and bile salts. The body is capable of supplying the required amount of cholesterol from a small food intake. Foods that are high in saturated fats are red meat, full fat dairy products and eggs.

Carbohydrates: these are simple or more complex forms of sugar molecules which are broken down by the digestive processes into glucose. Glucose is absorbed into the blood stream and utilized by the body. Processed food such as biscuits, pasta, sweets, cakes, chocolates and sauce consist mainly simple sugar that provides the body with calories (i.e. energy molecule in the form of glucose). Over consumption of such foods could lead to obesity, diabetes, atherosclerosis and tooth decay. Starches are complex carbohydrates comprising chains of glucose molecules. Foods such as cereals, grains, fruits, vegetables, bread and potatoes are mainly composed of starch and they also contain fibre, vitamins and minerals. These foods prevent obesity and over weight problems.

Fibre: This is found in the cell walls of plants and thus is present in plant-based foods. Fibre occurs in various forms and the most common is cellulose, the main constituent of the cell walls of plants. Foods rich in cellulose are foods containing whole-wheat bran such as wholemeal flour and bread, wholemeal pasta and brown rice. Cellulose is insoluble fibre; it does not break down in water. It binds to water and adds bulk to the waste products of digestion and facilitates efficient operation of bowel. Other forms of fibre are pectins found in fruits, citrus peel and vegetables and hemicelluloses found in oat bran, seeds, peas, beans, grains, vegetables and fruits. These two forms of fibre have gel-producing effects, are able to bind to cholesterol and excess bile salts and promote a slower release of food from the stomach, allowing more time for nutrients to be broken down and absorbed. Hemicelluloses are important sources of helpful fatty acids, provide energy for cells in the lining of colon. A well known form of hemicellulose is porridge (from oats).

Vitamins: They are required in metabolic processes such as growth and repair of tissues and organs, utilization of food and functioning of the immune, nervous, circulatory and hormonal systems. Vitamins are either fat soluble or water soluble. Fat soluble vitamins include vitamin A, D, E and K. These types of vitamins (with the partial exception of D and K) are derived from food and the excess is stored by the liver. Any excessive intake of fat soluble vitamins, especially A and D, (which may result from an overdose of supplements) can have toxic effects due to their accumulation in the liver. The water soluble vitamins are C and the B group. These vitamins dissolve in water and cannot be stored in the body and they must be derived from food daily. The excess of these vitamins is simply excreted.

Minerals: These are present in rocks, metals and living beings and they play an important role in metabolic processes such as combating illness and the effects of ageing. Minerals such as calcium and phosphorus are present in significant amounts in our bones and teeth. On the other hand, iron, iodine and sodium occur in very small quantities. Minerals needed in minute amounts are called trace elements. For example, sodium which is readily obtained from natural foods is essential in minute quantities for the correct functioning of nerves and as a vital constituent of cellular and tissue fluids. Potassium is an important component of cell and tissue fluids, helping to maintain the electrolyte–water balance and is also essential for nerve function. In particular, the imbalance in potassium and sodium levels in the body may lead to development of diseases. A low potassium/high sodium ratio is a factor in the development of high blood pressure and stress.