What is Protein? Learn How Much Protein is Needed for a Balanced Diet
Protein is one of the three main types of molecules found in food, the others being carbohydrate and lipid (fat). Protein is used in every cell in the body for catalyzing chemical reactions, as a structural component, for communication among cells, and in the “epigenome,” which surrounds our genes. It is necessary for cell repair and new cell growth, and it is found in almost every body fluid.
Protein in the Body
Proteins are comprised of chains of molecules called amino acids. Although there are many amino acids, all life on earth, including humans, uses only twenty different amino acids. In a protein, the amino acids are linked by chemical bonds called peptide bonds. Proteins are the only major food molecules to contain nitrogen, which is an essential atom in the peptide bond.
The human body can manufacture some amino acids, but not others, which must be obtained through the diet. Because they must be consumed in food, these are called the essential amino acids, and foods containing all the essential amino acids are called complete proteins.
Too Little Protein in the Diet
A daily intake of 1.5 grams of protein per kilogram of body weight is considered sufficient (Millward, 1999). That’s about 100 grams of protein, dry weight, for a 150-pound person. Most people who eat animal products take in more than enough protein in their diet to meet their needs. Some special populations, such as pregnant women and infants, need more protein, but even they usually have no difficulty getting enough protein; for example, though lower in protein than cows’ milk, breast milk contains the appropriate amount of protein for growing infants. Those who follow a vegan diet should pay attention to ensure they consume enough plant protein of the proper kinds each day, since most plant foods are lower in protein than animal products are.
Too Much Protein in the Diet
There is evidence that a diet too high in protein may carry health risks. A high dietary level of protein may be harmful to kidney function, especially in those with underlying kidney disease. Most people who eat high-protein diets consume it in the form of meat, and meat-heavy diets are known to contribute to a painful disease called gout. They are also linked to high cholesterol and coronary artery disease.
A high-protein diet is not the same as a low-carbohydrate diet such as the Atkins Diet. Low-carbohydrate diets may or may not be high in protein and may also be high in fat. High-protein diets are sometimes favored by bodybuilders, but not all authorities believe a high-protein diet is necessary for building muscle (for example, see Kleiner, 1997).
References
Kleiner, Susan M., 1997. “Nutrition for Muscle Builders.” The Physician and Sports Medicine 25:8.
Milward, D. Joe, 1999. “Optimal intakes of protein in the human diet.” Proceedings of the Nutrition Society 58, pp. 403-413.