How much protein do we need to be healthy? Aptly enough, the word "protein" is derived from a Greek root meaning "of first importance", and protein - which constitutes about one-fifth of an adult's body weight - is the basic material of life.
Proteins are constantly being broken down in our bodies.
Most of the amino acids are reused, but we must continually replace some of those that are lost.
Without dietary protein, growth and all bodily functions would not take place.
The 13 amino acids our body can make are known, somewhat confusingly, as the "nonessential" amino acids.
They are in fact essential, but not as part of our diet.
The nine "essential" amino acids are those we have to eat.
We can either get them from plant protein directly or by eating animals that consume plants and animals.
Getting Complete Protein Nutritionists use the phrases "complete protein" and "incomplete protein" to describe the proteins provided by various foods.
If a food supplies a sufficient amount of the nine essential amino acids, it is called a complete protein.
Virtually all proteins from animal foods are complete.
Foods that lack or are short on one or more of the essential amino acids - such as some fruits, grains, and vegetables - are called incomplete proteins.
Such plant-derived foods can nonetheless be excellent sources of protein if eaten in combinations that supply all of the essential amino acids.
For example, the amino acids missing in a vegetable can be provided by eating a grain product, another vegetable, or an animal-derived protein at the same meal.
Animal vs.
vegetable Meat and other animal products are the most readily available sources of complete protein.
The protein content, by weight, of cooked meat, fish, poultry, and mild solids is between 15 and 40 percent.
The protein content of cooked cereals, beans, lentils and peas ranges from 3 to 10 percent.
Potatoes, fruits, and leafy green vegetables come in at 3 percent or lower.
Soybeans and nuts have a protein content comparable to meat, but, depending upon how they are prepared, their proteins may not be as easily digested.
However, recent research suggests that in a mixed or even totally vegetarian diet, the issue of digestibility is not too important.
For someone eating a whole grain and vegetable diet, no more than 15 percent of the protein consumed would be unavailable because of problems with digestibility.
The fact that we are omnivorous, that is, we can eat both meats and plants, has contributed to the survival of the human species.
But as anthropologists have pointed out, human beings have overwhelmingly preferred meat to other foods.
And a number of experts attribute the general good health, increased height, and longevity of people of developed countries today to their high-protein diets.
Protein Requirements The body cannot store protein, so it needs a fresh supply every day.
If, like most Americans, you consume mostly high-quality protein, your total requirement will there fore be slightly less.
If you get almost all your protein from plant sources, it will be slightly greater.
Children under eighteen need some additional protein to allow for growth, and the younger they are, the more protein they need per pound of body weight.
Pregnant women are allocated an additional 10 grams of protein per day by the RDA, lactating mothers an extra 12 to 15 grams during the first six months.
Sources of Protein The foods below (click here to view the full chart) are all good sources of protein.
The listed protein amounts are averages.
Many foods that are relatively high in protein are also high in fat, so the chart indicates the percentage of fat accompanying each food.
Try to limit your intake of protein sources that derive more than 30 percent of their calories from fat.
Food Source Dairy and Eggs Protein (Grams) Fat Calories Cheddar cheese, 1 oz.
7 70% Cottage cheese (2%), 1/2 cup 16 17% Egg, 1 medium 6 68% Ice cream, hard, vanilla, 1/2 cup 2 48% Milk, skim, 1 cup 8 5% Mozzarella, part skim, 1 oz.
8 56% Ricotta, part skim, 1/2 cup 10 53% Yogurt, low-fat, plain, 1 cup 12 25% Meat and Fish (4oz.
) Protein (Grams) Fat Calories Chicken, light meat, roasted, no skin 31 26% Ground beef, extra lean, broiled 33 56% Sirloin steak, choice cut, trimmed, broiled 35 37% Tuna, canned, in water 33 12% Turkey breast, roasted, no skin 24 6% Grains Protein (Grams) Fat Calories Oatmeal, 1 cup cooked 6 12% Rice, brown, 1 cup cooked 5 4% Spaghetti, 1 cup cooked 6 5% Whole wheat bread, 2 slices 6 13% Legumes and nuts Protein (Grams) Fat Calories Almonds, 1 oz.
6 82% Cashews, dry roasted, 1 oz.
4 71% Lentils, 1/2 cup cooked 8 4% Lima beans, 1/2 cup cooked 8 3% Peanut butter, 2 Tbsp.
10 76% Red kidney beans, 1/2 cup canned 8 4% Soybeans, 1/2 cup cooked 10 33% Tofu, 4 oz.
9 55%