Nutrients

The foods we eat contain thousands of different chemicals. However, only a few dozen of these chemicals are absolutely essential to keep us healthy. These few dozen are the nutrients, the substances we must obtain from the foods we consume. Nutritionists classify nutrients into six main groups: water, carbohydrates, fats, proteins, minerals, and vitamins. The first four groups are called macronutrients, because the body needs them  in large (or macro) amounts.  The last two are required in only small quantities and so are known as micronutrients.

•   WATER

Water is needed in great amounts because the body consists largely of water. Usually, between 50 and 75 percent of a person’s body weight is made up of water. The body requires large quantities of carbohydrates, fats, and proteins because these nutrients provide energy. The energy in food is measured in units called kilocalories. A kilocalorie is equal to 1,000 calories. A calorie is the amount of energy required to raise the temperature of one gram of water one Celsius degree. However, kilocalories are often referred to as simply “calories.”

• CARBOHYDRATES

Carbohydrates include all sugars and starches. They serve as the main source of energy for living things. Each gram of carbohydrate provides about 4 calories. (A gram is about 0.035 ounce.) There are two kinds of carbohydrates--simple and complex. Simple carbohydrates, all of which are sugars, have a simple molecular structure. Complex carbohydrates, which include starches, have a larger and more complicated molecular structure that consists of many simple carbohydrates linked together. 

• Fats

Fats are a highly concentrated source of energy. Each gram of fat provides about 9 calories. All fats are composed of an alcohol called glycerol and substances called fatty acids. A fatty acid consists of a long chain of carbon atoms, to which hydrogen atoms are attached. There are three types of fatty acids: saturated, monounsaturated, and polyunsaturated. A saturated fatty acid contains as many hydrogen atoms as its carbon chain can hold. A monounsaturated fatty acid is lacking a pair of hydrogen atoms. In a polyunsaturated fatty acid, the carbon chain contains at least four fewer hydrogen atoms than it could hold. 

• PROTEINS

Proteins provide energy--like carbohydrates, 4 calories per gram but more importantly, proteins serve as one of the main building materials of the body. Muscle, skin, cartilage, and hair, for example, are made up largely of proteins. In addition, every cell contains proteins called enzymes, which speed up chemical reactions. Cells could not function without these enzymes. Proteins also serve as hormones and as antibodies.

• MINERALS

Minerals are needed for the growth and maintenance of body structures. They are also needed to maintain the composition of the digestive juices and the fluids that are found in and around the cells. People need only small amounts of minerals each day. Unlike vitamins, carbohydrates, fats, and proteins, minerals are inorganic compounds. This means that they are not created by living things. Plants obtain minerals from the water or soil, and animals get minerals by eating plants or plant-eating animals. Unlike other nutrients, minerals are not broken down within the body.

• VITAMINS

Vitamins are essential for good health. Small amounts of these compounds should be supplied daily in the diet. Vitamins regulate chemical reactions in which the body converts food into energy and tissues. There are 13 vitamins: vitamin A; the vitamin B complex, which is a group of 8 vitamins; and vitamins C, D, E, and K. Scientists divide vitamins into two general groups, fat-soluble vitamins and water-soluble vitamins. The fat-soluble vitamins--vitamins A, D, E, and K--dissolve in fats. The vitamins of the B complex and vitamin C dissolve in water.