|Much has been said about protein in our diets - that we need it (as of course we do), that athletes should load up on it, that not all proteins are created equal, that we eat too much protein and should therefore cut down our consumption of meat and dairy products and fall back on fruits and vegetables to maintain ourselves.
How much protein do we need to be healthy?
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. Muscles,
organs, bones, cartilage, skin, antibodies, some hormones, and all enzymes
(the compounds that direct chemical reactions in cells) are made of protein.
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. This process is known as protein turnover. Our need to keep this
process going begins at conception and last throughout life. Without dietary
protein, growth and all bodily functions would not take place.
While plants and some bacteria can manufacture all the amino acids they
need, the human body can manufacture only thirteen. The amino acids we
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.
When we eat foods containing protein, the digestive system breaks it down
to the constituent amino acids, which enter the body "pool"
of amino acids. Each cell then assembles the proteins it needs using the
building blocks available. If, however, one or more of the needed amino
acids is in short supply or not available at all, others that may be on
hand cannot be utilized to form a protein. This is why it is important
to eat a diet that contains all of the essential amino acids plus enough
additional amino acids to allow for synthesis of the "nonessential" amino acids.
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
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
body cannot store protein, so it needs a fresh supply every day. The Food
and Nutrition Board of the National Academy of Sciences has established
a daily Recommended Dietary Allowance (RDA) for protein based on a person's
age and weight. According toe the Academy, because most people in the
United States eat meat and dairy products regularly, the average protein
intake is higher than what most people need. So you should easily meet
the following RDAs:
The RDA for adults is 0.8 grams of protein for each kilogram (2.2 pounds)
of body weight. This works out to 44 grams for a 120 pound person, 55
grams of protein for a weight of 150 pounds, and 66 grams for 180 pounds.
These allowances assume that you eat a mixed diet of proteins - some high-quality
(complete), some low-quality (incomplete).
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. The variation due to the type of diet is no more than approximately
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
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
Did you know?
Beans provide nearly as much protein as meat, and are much lower in
fat and calories. One cup of cooked beans contains 12 to 25 grams of
protein, which is 25 to 50 percent of the RDA.
foods below 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.
cheese, 1 oz.
cheese (2%), ½ cup
cream, hard, vanilla, ½ cup
skim, 1 cup
part skim, 1 oz.
part skim, ½ cup
low-fat, plain, 1 cup
and fish (4 oz.)
light meat, roasted, no skin
beef, extra lean, broiled
steak, choice cut, trimmed, broiled
canned, in water
breast, roasted, no skin
1 cup cooked
brown, 1 cup cooked
1 cup cooked
wheat bread, 2 slices
dry roasted, 1 oz.
½ cup cooked
beans, ½ cup cooked
butter, 2 Tbsp.
kidney beans, ½ cup canned
½ cup cooked