Food supplies the nutrients (nourishing substances) that the body needs for (1) producing energy, (2) building and repairing tissues, and (3) regulating body processes. The main kinds of nutrients are water, carbohydrates, fats, proteins, minerals, and vitamins. Each kind of nutrient plays an important role in keeping the body healthy. Many foods are highly nourishing, but no one food supplies every necessary nutrient.

As the body digests food, the food is broken down into the various nutrients. The food eventually enters the small intestine, and the nutrients pass through the intestinal wall into the bloodstream. The blood distributes the nutrients to cells throughout the body.

In addition to nutrients, food supplies other important substances, especially water and fiber. Every living thing must maintain a certain water supply, or it will die. Fiber adds bulk to food and keeps waste products moving through the intestine.

People who do not get enough food to eat suffer from undernutrition. A person whose diet seriously lacks any nutrient is said to be malnourished. Some malnourished people have plenty of food, but they choose to eat foods that do not supply all the necessary nutrients. Some people develop health problems because they eat too much and become overweight.

A moderate, well-balanced diet can help ensure good health. For detailed information about the foods that contribute to a healthful diet.