Nutrients are certain chemical compounds that are present in foods and that fulfill one or more of the following functions:

• Supply energy for body functions.
• Build and replace cells that make up body tissues.
• Regulate body processes.

There are six categories of nutrients:

• Carbohydrates
• Fats
• Proteins
• Vitamins
• Minerals

• Water

Proteins

Proteins are known as the building blocks of the body. They are essential for growth, for building body tissues, and for basic body functions. They can also be used for energy if the diet does not contain enough carbohydrates and fats.

Proteins consist of substances called amino acids. The body is able to manufacture many of them, but there are nine amino acids it cannot manufacture and must get from foods. A food protein that contains all nine essential amino acids is called a complete protein. Meats, poultry, fish, egg and dairy products contain complete proteins.

Proteins that lack one or more of these essential amino acids are called incomplete proteins. Foods high in incomplete proteins include nuts, grains, and dried beans and other legumes. Foods that, if eaten together, supply all the amino acids are called complementary proteins.

For example, cornmeal tortillas topped with chili beans supply complete protein because the corn supplies the amino acids lacking in the beans. Beans and rice is another example of a food combination supplying complementary proteins.

The average adult needs about 50 to 60 grams of protein a day. For most North Americans, getting enough protein daily is not a problem; most get about twice as much as they need. Greatly excessive protein in the diet can lead to a variety of health problems, including kidney and liver damage.

Vitamins

Vitamins are present in foods in extremely small quantities, but they are essential for regulating body functions. Unlike proteins, fats, and carbohydrates, they supply no energy, but some of them must be present in order for energy to be utilized in the body.

Also, lack of certain vitamins causes deficiency diseases.

Vitamins are classified as water soluble and fat soluble. The water-soluble vitamins (the B vitamins and vitamin C) are not stored in the body and must be eaten every day.

Foods containing these vitamins should be handled so the vitamins are not dissolved into the cooking water and lost.

Fat-soluble vitamins (A,D, E and K) can be stored in the body, so they do not need to be eaten every day as long as the total amount eaten over time is sufficient.

Consuming too much of a fat-soluble vitamin daily, as sometimes happens when people take too many vitamin supplements, can result in toxic levels of the vitamin stored in the tissues.

Minerals

Minerals, like vitamins, are consumed in very small quantities and are essential for regulating certain body processes. Minerals that must be consumed in relatively large amounts-more than 100 milligrams daily-are called major minerals. These include calcium ,chloride, magnesium, phosphorus, sulfur, sodium and potassium. Minerals that must be present in smaller amounts are called trace minerals. These include chromium copper, fluoride, iodine, iron, manganese, molybdenum, selenium and zinc.

Less is known about the functions of some of the trace minerals. It is important to understand, however, that although small quantities are needed by the body, too much of any of them can be harmful.

Sodium, a component of table salt, is well known as a health problem. Too much sodium is thought to contribute to high blood pressure. Health authorities try to convince people to reduce the sodium in their diets, primarily by salting foods less.

Water

The adult human body is 50 to 60 percent water by weight. Water plays a role in all the body’s functions, including metabolism and other cell functions, digestion, delivery of nutrients, removal of waste, temperature regulation, and lubrication and cushioning of joints and tissues.

Water forms a large part of most of the food we eat and all the beverages we drink.

The body is good at regulating its own water content and tells us when we need more by making us feel thirsty. This signal should not be ignored. Even better is to drink enough fluids to prevent feeling thirsty. Required daily water intake varies greatly from person to person, depending on age, level of activity, and environmental factors such as heat.

The common recommendation of 8 glasses of water a day is not enough for some people, such as athletes and others who exercise strenuously, and is too much for others, such as older, sedentary adults.