Carbohydrates are divided into two groups sugars (e.g., in fruits, honey, and jellies) and starches (e.g., bread, potatoes, and rice). When taken in excess, carbohydrates are converted to adipose (fat) tissue and contribute to an overweight condition. When carbohydrates are taken too sparingly, the body metabolized its fats and then its protein resources, and this eventually contributes to undesirable weight loss.
Fats are nutritive substances that compose the most concentrated source of energy of all the elements. Similar to carbohydrates, they provide the body with work and heat-energy resources. Fats function as carriers for the fat-soluble vitamins (A, D, E, and K), as padding for the organs and subcutaneous tissue, and as an energy resource when stored as adipose tissue. Common sources of fats are butter, milk, oil, and fatty meats. They are not as easily or quickly metabolized as carbohydrates and in excess contribute to overweight, digestive, and cardiovascular problems.
Proteins are the most important element required by the body for tissue growth, development, maintenance, and repair. They are the main structural unit of all living cells. Proteins are expensive sources of energy, since the body does not maintain reserve stores. Because of this, a constant source of protein is required in the daily diet to avoid a deficiency condition. Some of the best sources of protein are found in meat, fish, eggs, and legumes (e.g., peas and beans).
Vitamins are natural components of most foods and are essential for proper growth and maintenance of health. They are needed by the body in minute amounts but play a vital role in metabolism, helping to convert carbohydrates, fats, and proteins into energy. It should be noted that they do not furnish energy or act as tissue-building materials. Some vitamins can be stored in the body; thus, in some people, vitamin abuse can be dangerous. An example of this is the excessive use of vitamin A. Vitamins are classified as either water-soluble or fat-soluble. Niacin, folic acid, vitamin B complex, and vitamin C are transported throughout the body in water and are classified as water-soluble. These vitamins are not stored in the body to any great extent and excesses in intake are generally excreted by the kidneys. Vitamins A, D, E, and K are transported throughout the body in fats and are called fatsoluble. As stated above, many fat-soluble vitamins are stored in the body.
Although the mineral elements constitute only a small portion of the total body composition, they are essential in the building and maintenance of bones, teeth, and various body systems. Some minerals are found in large amounts in the body. Others, detectable in small amounts, are referred to as trace minerals. Regardless of the quantitative amounts, those mineral essential to support and maintain optimal health are calcium, phosphorus, magnesium, iron, iodine, potassium, sodium, chlorine, sulfur, and fluorine.
For mineral needs to be met satisfactorily, the consumption of each element must be sufficient to cover body tissue requirements and to meet the changing physiological needs due to growth or environmental changes. It was once believed that any diet adequate in other respects would also provide an adequate intake of the essential minerals. This is not true. Different foods vary greatly in their mineral content and the same type of food produced in various geographic localities may differ considerably in the percentage composition of the individual minerals. The differences in an individuals eating habits may also result in considerable variation in the mineral intake.
Water, although not a food, is essential for the maintenance of life and health and is an integral part of most foods. It is by far the largest single constituent of the body, comprising almost two-thirds of the total body weight. Of the substances essential to life, water stands second only to oxygen. Without oxygen, humans can survive only a few minutes; without water, they may survive for a period of hours or a few days, depending upon many circumstances.
Water is the great solvent in the body. All basic body constituents are held in water, and it is the medium in which all chemical reactions take place in the body. It functions as a vehicle for nutrients, secretions, and most body substances; and because it is an essential element of the protoplasm of cells, it serves as a building material for growth and repair.
To maintain metabolic equilibrium, water intake must equal water output. The water loss through urine, feces, skin, and lungs must be replaced by water in food, water from the oxidation of food, and fluid intake. Under normal conditions, thirst is usually an adequate guide of the water requirement. When the body is in negative water balance, the condition known as dehydration results. Among its effects are the following: