A nutrient is a substance found in food and needed by the body for life and health. Nutrition scientists today have identified about 40 essential nutrients, which are classified as vitamins, minerals, amino acids (building blocks of proteins), essential fatty acids (in fats), and water. “Essential” means we must obtain these nutrients from our diets either because we cannot make them at all in our bodies or we cannot make enough of them. In addition, we need carbohydrates, fats, and proteins as fuel for energy; an ideal fuel mix is probably about 12 percent calories from proteins, 30 to 35 percent from fats, and the rest from carbohydrates.
Although individual nutritional requirements vary, all of us have a continual need for nutrients from each group – for energy, growth, replacement, and maintenance of body tissue, and for regulation of vital physiological processes. Understanding the roles nutrients play enables us to appreciate their value and to determine optimum individual needs, avoiding excesses that may be wasted or may build up in the body in potentially harmful amounts, or deficiencies that will prevent the body from operating at its peak.
All the nutrients needed for a healthy human body are obtained from food or are manufactured by the body. The food we eat, however, must undergo dramatic physical and chemical changes in order for the essential nutrients it contains to be used to fuel the body. These changes are carried out in the digestive system.