Protein & Diet

Protein is an essential nutrient for cell maintenance and repair, and regulation of a wide range of bodily functions. How much protein we need to eat in our diet usually depends on our ideal body weight. Ideal body weight is used because amino acids are not needed by fat cells, only by our lean body mass.

Protein & Diet – Amino Acids

Protein is made up of amino acids, like building blocks. Proteins from different foods in our diet contain different amino acids. There are 22 amino acids, divided into essential and non-essential amino acids. Essential amino acids must appear in our diet because they cannot be made by the body. The 8 essential amino acids we must eat in our diet include: isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine.

Protein & Diet – US Guidelines on Protein and Diet

The Recommended Daily Allowance (RDA) of protein according to U.S. government standards is 0.8 gram per kilogram (2.2 pounds) of ideal body weight for the adult. This protein RDA is said to meet 97.5% of the population’s needs.

For more, see Protein Needs in Diet

Protein & Diet – Percentage of Calories as Protein

The protein RDA suggests that we eat approximately 10-15 percent of calories as protein in our daily diet.

World Health Organization (WHO) Guidelines on Protein and Diet

The US RDA protein diet standards may be overestimated. The WHO Organization more conservatively puts our dietary protein needs at about half of the U.S. government minimum levels, or 0.45 grams of protein per kilogram of ideal body weight. Although differing weight standards and food sources of protein may apply.

Protein & Diet – Food Sources of Protein

National and international recommendations for protein intake are based on animal sources of protein such as meat, cow’s milk and eggs. Plant proteins may be less digestible because of intrinsic differences in the nature of the protein and the presence of other factors such as fiber, which may reduce protein digestibility by as much as 10 percent.

Protein & Diet – Plant Sources of Protein in Vegan Diet

The main protein foods in a vegan diet are pulses (peas, beans & lentils), nuts, seeds and grains, all of which are relatively energy dense. As the average protein level in pulses is 27 percent of calories; in nuts and seeds 13 percent; and in grains 12 percent, it is easy to see that plant foods can supply the recommended amount of protein as long as the energy requirements are met.

Protein & Diet – Plant Sources of Protein Quite Adequate

Furthermore, dietary studies show clearly that diets based solely on plant sources of protein can be quite adequate and supply the recommended amounts of all essential amino acids for adults, even when a single plant food, such as rice, is virtually the sole source of protein. The American Dietetic Association emphasizes that protein combining at each meal is unnecessary, as long as a range of protein rich foods is eaten during the day.

Protein Deficiency

The name for protein deficiency disease is kwashiorkor. Protein deficiency is a wasting disease that in its severe state leads to death. It is curable, of course, with consumption of complete protein foods or supplements. Marasmus, another protein deficiency disease associated with calorie or food deficiency, comes from a starvation diet and results in complete loss of energy and tissue wasting. Also called “protein-calorie malnutrition” (PCM), it is the world’s most widespread and correctable malnutrition problem, killing millions yearly. See also Nutritional Deficiencies.

NOTE: For a short guide to how we digest protein, see Food Digestion and Protein Digestion.

Sources include:

1. Food and Agriculture Organization/ World Health Organization/ United Nations University (1985). ‘Energy and protein requirements’, WHO Technical Report Series 724. Geneva, WHO.

2. Position of the American Dietetic Association: vegetarian diets – technical support paper’, J. Am. Diet. Assn., 88, 352-355.