Diet and nutrition

What is nutrition?

Nutrition is the science of turning food into fuel for the body. Good nutrition has many benefits for good health. The body needs adequate amounts of specific nutrients from six categories: carbohydrates, proteins, fats, vitamins, minerals, and water. Sugar, starch, and cellulose are all carbohydrates. The chemical structure of fats makes them either saturated or unsaturated. Cholesterol is a fat-like substance. Proteins are composed of many amino acids. High-quality proteins contain adequate amounts of all essential amino acids while low-quality proteins do not. Some minerals are needed in relatively large amounts. Others are called trace elements because they are needed in very small amounts. Water is also essential. Each nutrient performs specific functions in the body and what's more, the functions of many nutrients are interrelated. Each type of food has a similar nutrient content, although specific values vary. A varied diet helps ensure nutritional adequacy. The table below illustrates the interlocking pattern of nutrients.

Table 1. The Interlocking Pattern of Nutrients

Milk and milk products	Breads and cereals	Fruits and vegetables	Meat and alternates
Protein Fat ------------------ ------------------ Riboflavin Niacin Folacin Vitamin B12 ------------------ Vitamin A Vitamin D Calcium ------------------ ------------------	Protein ------------------ Carbohydrate Thiamin Riboflavin Niacin Folacin ------------------ ------------------ ------------------ ------------------ ------------------ Iron Fibre	------------------ ------------------ Carbohydrate Thiamin ------------------ ------------------ Folacin ------------------ Vitamin C Vitamin A ------------------ ------------------ Iron Fibre	Protein Fat ------------------ Thiamin Riboflavin Niacin ------------------ Vitamin B12 ------------------ Vitamin A ------------------ ------------------ Iron Fibre

Food, then, is required for energy, growth and repair of body tissues, and for the regulation of body processes. The body requires 45 different nutrients, whose classification system has been described above and whose functions are outlined in our convenient at-a-glance reference sheet (PDF file).

Carbohydrates

First, carbohydrates are composed of carbon, oxygen and hydrogen. They are organic substances. Sugars exist as simple sugars, called monosaccharides, and double sugars, called disaccharides. The simple sugars are glucose, a simple sugar found in blood, and fructose, found in most fruits and vegetables. The double sugars are sucrose, a commercial sugar or table sugar, lactose or milk sugar, and maltose, found in breads and cereals. Starches are multiple sugars chemically bonded in long chains. They are responsible for the maintenance of energy. Cellulose is the final type of carbohydrate. It is a fibrous substance found in fruits, vegetables, and the bran of grains. It cannot be digested by the body and therefore, serves to clean the intestinal tract and to provide bulk to the diet.

Food sources of carbohydrates are grain products, potatoes, table sugar, syrups, and fruits.

Carbohydrates serve to provide the body with quick sources of energy. Insufficient amounts of carbohydrates may result in weight loss, fatigue and general lack of energy. A severe deficiency will result in marasmus.

Proteins

The second class of nutrient consists of proteins, which are made up of many amino acids. Ten of these are known as essential amino acids and must be obtained from the diet, as the body is incapable of producing them. Complete proteins contain all the amino acids, whereas incomplete proteins lack some of the essential amino acids. Complete proteins are those found in meats. Incomplete proteins are obtained from vegetables.

Other food sources of complete proteins include animal sources, milk, eggs, cheese, fish, and poultry. Other sources of incomplete proteins are vegetables, fruits, nuts, legumes, peas, beans, and lentils.

Proteins serve to build and repair body tissues and like carbohydrates, supply energy. The latter is demonstrated in periods of fasting, when the body converts proteins from muscle tissue to energy for use by the body.

Not only are muscles made of proteins, but all body tissues contain some proteins.

Fats

Fats comprise the third group. There are two kinds of fats, saturated and unsaturated. Saturated fats are those that are solid at room temperature, while unsaturated fats are liquid at room temperature.

Animal sources of fat are bacon, butter, cream, egg yolks, and fat meats. Vegetable sources of fats are nuts, corn oil, olive oil, sunflower oil, soybean oil, and nuts.

Fats are used by body cells or temporarily stored in the liver. Excess fats are stored as body fat in adipose tissue. Fats also carry the fat-soluble vitamins A, D, E, and K. Subcutaneous fat (fat below the skin) serves as a thin layer of insulation in cold weather. Fat also serves to protect internal organs from punctures, sudden jars and jolts, and may also prevent them from touching each other, causing friction.

Vitamins

The fourth group consists of the vitamins. Fat-soluble vitamins, such as vitamins A, D, E, and K are stored in the liver and adipose tissues. They must have protein carrier molecules to carry them to their destinations.

Water-soluble vitamins such as thiamin, riboflavin, the B complex vitamins, folic acid, and vitamin C are required daily. These vitamins may be lost through improper food preparation. They travel freely through the circulatory and lymphatic systems, to be stored in lean tissues for a month or more. Excess vitamins are excreted by the kidneys.

Vitamin A ensures that the skin and hair are healthy. It also helps to maintain a state of resistance to infection of the eyes, respiratory tract and digestive system. It is required for good eyesight. Food sources of vitamin A are fish liver oil, butter, cream, and dark green and dark yellow vegetables.

Vitamin D is known as the sunshine vitamin and works to help the body to better use calcium and phosphorus. It can be obtained from such food sources as fish liver oils and milk enriched with vitamin D.

Vitamin E has significant functions in relation to human metabolism. It speeds up healing. It can be obtained from foods such as vegetables oils, milk, eggs, meats, cereals, and leafy vegetables.

Vitamin K is essential for clotting of the blood, should a person become wounded or the blood's viscosity very thin. It is found in green, leafy vegetables, liver, soybean, and vegetable oils.

Thiamin maintains healthy nerves and is needed for the metabolism of carbohydrates. It is found in fruits, vegetables, whole grain, and enriched cereal products.

Riboflavin helps keep the skin, mouth and eyes healthy, and helps to maintain resistance to infection. Food sources of riboflavin are milk, meat, whole grain, enriched grain products, fruits, and vegetables.

Niacin increases resistance to infection and prevents pellagra. Sources of niacin include milk, meat, dark green and deep yellow vegetables, whole grain and enriched grain products.

Ascorbic acid, or vitamin C as it is more often called, increases resistance to infections and also keeps teeth and gums in good condition. It can be found in citrus fruits, green and yellow vegetables, milk, and meat.

Insufficient consumption of vitamins may cause severe deficiencies. Deficiencies of niacin can cause pellagra, an illness characterized by diarrhea, dementia, and dermatitis. Lack of vitamin A can result in kerophthalmia, an eye disease that can result in blindness. Deficiency of thiamin results in beri-beri, or numbness of the feet, legs, arms and muscles, as well as degeneration. Lack of vitamin C will result in scurvy, characterized by loss of weight, sore, bleeding and swollen gums and loss of teeth. Lack of vitamin D causes an illness called ostemalacia, or softening of the bones in the wrists and ankles. Another consequence of insufficient vitamin D is rickets, or bow-leggedness, and knocked knees.

Minerals

Minerals are chemical elements, rather than organic compounds, necessary for the health and maintenance of body functions.

A key constituent of bones and teeth, calcium is essential for vital metabolic processes such as nerve function, muscle contraction, and blood clotting. Calcium is commonly found in dairy products. A lack of calcium may result in osteomalacia, osteoporosis, rickets, or tetany.

Iron is essential for the transfer of oxygen between body tissues. Hemoglobin carries iron throughout the circulatory system. Iron may be found in eggs, liver, fortified foods such as cereals and white flour, meat, nuts, peas, whole grains, and in green, leafy vegetables. A lack of iron can lead to anemia and an increased susceptibility to infections.

Magnesium is essential for healthy bones and aids in the formation of compounds needed for energy conversion. Magnesium is found in milk, most fruits, pulses, and leafy, green vegetables. A lack of magnesium may lead to anemia, demineralization of bones, nerve disorders, respiratory problems, weakness, and weight loss.

As the main base ion of intercellular fluid, sodium maintains the pH balance of the body and is necessary to maintain the electrical potentials of the nervous system and the functioning of muscle and nerve tissues. Sodium is found in processed bakery products, table salt and in processed foods such as canned goods and cured products. Insufficient sodium in the diet may lead to low blood pressure general muscle weakness or paralysis, mild fever, and respiratory problems. Excess sodium, on the other hand, may lead to dehydration and hypertension.

Other minerals needed in trace amounts include chromium, copper, manganese, selenium, sulphur, and zinc.