Celeste Robb-Nicholson, M.D.

Harvard Health Letters

Q. How much protein do I need every day? Does it matter what kind I eat?

A. Protein is essential. It forms the structure of the cells in our bodies and participates in almost every cell activity necessary for growth, development, and tissue repair. Protein also supplies fuel for meeting the body's energy needs. In the normal course of metabolism, the protein in our bodies is broken down into smaller molecules called amino acids. Some of these amino acids are used as fuel. Others are reassembled into protein molecules to replace the protein used each day by our cells.

The protein we eat is also broken down into amino acids. Some of these are "essential amino acids," so named because the body can't make them, and they must be obtained through food. We don't need to get all the essential amino acids in every protein source, but we do need all of them in our diets. We can't store amino acids, so we need to replenish them daily through the proteins we eat.

The amount of dietary protein we need every day depends, in part, on weight and physical activity. Some people need to restrict their protein intake because of kidney dysfunction or a metabolic disorder. But for the average healthy adult, the Recommended Dietary Allowance (RDA) is 0.8 grams of protein per kilogram of body weight per day. (One kilogram equals 2.2 pounds.) That's about 46 grams for a 128-pound woman.

The RDA is higher during childhood, pregnancy, lactation, and recovery from a serious illness, trauma, or major surgery -- when our bodies have increased protein needs. Very active people and athletes in training probably need more protein as well, but no special RDAs have been established for such individuals.

The Institute of Medicine recommends that adults get 10 percent to 35 percent of total daily calories from protein. The percentage should reflect changes in diet and activity level. For example, if a woman reduces her calorie intake, she should consume a larger proportion of those calories as protein, in order to meet her daily requirement.

Most animal sources of protein contain all the essential amino acids, but many vegetable sources do not. To get the full range of essential amino acids, vegetarians and vegans need to eat a variety of protein-containing plant-based foods every day. Animal and vegetable proteins have roughly the same effects in our bodies, but it's important to pay attention to what comes along with the protein when you make food choices.

For example, steak is a great source of protein but it's also a source of saturated fat. Poultry and fish are better animal sources of protein, and oily fish such as salmon also provide healthful omega-3 fatty acids. Beans and whole grains are good protein sources as well as excellent sources of fiber. -- Celeste Robb-Nicholson, M.D., Editor in Chief, Harvard Women's Health Watch

SOURCES OF PROTEIN

Food : Hard-boiled egg

Serving size: 1 large

Protein (grams): 6.3

Food: Cottage cheese, low-fat, 1 percent milkfat

Serving size: 1 cup

Protein (grams): 28

Food: Cheese, cheddar

Serving size: 1 oz

Protein (grams): 7.1

Food: Milk. 1 percent

Serving size: 1 cup

Protein (grams): 8.2

Food: Yogurt, plain, low-fat

Serving size: 1 cup

11.9 grams

Food: Beef, ground, 85 percent lean

Serving size: 3 oz.

Protein (grams): 22

Food: Chicken, roasted, white meat

Serving size: 3 oz.

Protein (grams): 26.7

Food: Turkey, roasted, white meat

Serving size: 3 oz.

Protein (grams): 25.1

Food: Salmon, sockeye

Serving size: 3 oz.

Protein (grams): 23.2

Food: Peanut butter, smooth

Serving size: 1 tablespoon

Protein (grams): 4.0

Food: Potato, baked, medium-sized

Serving size: 1

Protein (grams): 5.1

(Source: USDA National Nutrient Database for Standard Reference, Release 22, "Protein content of selected foods." To view it online: www.health.harvard.edu/usda-protein.)

 

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Health - How Much Protein Should I Eat?