Adults and developing children use food nutrition to fuel cellular growth, maintenance and repair. The process of metabolism transforms dietary protein, carbohydrates and fatty acids into usable energy, which enable the thousands of cellular functions that sustain human life. Damaged cells, such as wounded skin tissue, are repaired with the help of vitamin C. Because the lives of cells themselves are finite, with cells continually dying off and being replaced with new ones, you need a new supply of essential nutrients every day.
Your body uses the amino acids in dietary protein to form other proteins, build new body cells and generate energy for cellular functions. Protein in foods is known as complete, containing all the essential amino acids, or incomplete, lacking one or more of these elements. You get complete protein from animal-based foods such as fish, meats, eggs and milk. Eating a variety of different grains, fruits and vegetables, which contain incomplete protein, will supply all the amino acids[Ref 1, Medline]. Adults should get between 46 and 56 grams of protein per day[Ref 2, USDA, p. 76].
Of the three main types of carbohydrates, the body does not digest fiber for cellular use, but does convert sugar and starch into energy. You need these major sources of energy daily for every body process, including movement, thought, physical sensation, and respiration and other organ functions. Digestion breaks down dietary carbohydrates from foods such as bread, potatoes, beans, milk and apples to generate chemical energy[Ref 3, HSPH]. The U.S. Department of Agriculture recommends average carbohydrate intakes of 130 grams per day for all ages, adjusted to suit your activity level and health condition[Ref 2, USDA, p. 76].
Essential fatty acid classifications include saturated, monounsaturated and polyunsaturated fats, as designated by their molecular structures. Like carbohydrates, fats are present in different combinations in many foods. Animal-based meats and dairy products contain larger amounts of saturated fats than most plant-based foods. Nuts and seeds have greater monounsaturated fat, while vegetables and fruits may contain more polyunsaturated fat. Your body uses fatty acids for energy production. It draws on energy reserves from carbohydrates first during activity, and from fats second, during extended activity[Ref 4, Medline]. You should limit your total fat intake to 20 to 35 percent of all dietary calories[Ref 2, USDA, p. 76].
Dietary vitamin C from foods such as oranges, potatoes, tomatoes, melons and peppers assists in forming proteins used in cellular growth and scar tissue used to heal wounds. This essential vitamin works harder at night while you sleep, during a phase that the body uses for cellular growth and repair[Ref 5, NSF re tissue growth and repair occurs]. It also acts as an antioxidant to prevent environmental damage to your body, such as from smoke and radiation[Ref 6, Medline]. Your body can't store vitamin C, so you need between 75 and 90 milligrams from food daily[Ref 2, USDA, p. 76]