This article is from the Vegetarianism FAQ, by email@example.com (Michael Traub) with numerous contributions by others.
The short answer is: "No, sufficient protein can be obtained by
eating a variety of foods", but here is a longer explanation:
Protein is synthesized by the human body out of individual amino
acids. The body breaks down food into individual amino acids
and then reassembles the proteins it requires.
All amino acids must be present in the body to make proteins.
Those that can be synthesized from other amino acids are called
"unessential" amino acids. You can live on a diet deficient of
these if you eat enough extra of the other amino acids to
synthesize these. Those that cannot be synthesized from other
amino acids are called "essential" amino acids and must be
present in the diet.
Protein that contains all essential amino acids is called
"complete" protein. Protein that contains some, but not all
essential amino acids is called "incomplete" protein. It used
to be believed that all amino acids must be eaten at the same
time to form complete proteins. We now know that incomplete
proteins can be stored in the body for many days to be combined
with other incomplete proteins. As long as all essential amino
acids are in the diet, it does not matter if the proteins are
complete or incomplete.
The amount of protein recorded on food labels only lists the
complete proteins. A product may contain much higher amounts of
incomplete protein that is not listed. Combining such products
may increase the total amount of protein beyond the levels
The 1989 revision of the FDA's RDA suggests a protein intake of
44-63 grams. Many scientists think this number is too high.
Most scientists agree with this number.
Here is another (from "Physicians Committee for Responsible
THE PROTEIN MYTH
In the past, some people believed one could never get too much
protein. In the early 1900's, Americans were told to eat well
over 100 grams of protein a day. And as recently as the
1950's, health-conscious people were encouraged to boost their
protein intake. The reality is that the average American
takes in twice the amount of protein he or she needs. Excess
protein has been linked with osteoporosis, kidney disease,
calcium stones in the urinary tract, and some cancers. Despite
all this, many people still worry about getting enough
The Building Blocks of Life:
People build the proteins of their bodies from amino acids,
which, in turn, come from the proteins they eat. Protein is
abundant in nearly all of the foods people eat. A varied diet
of beans, peas, lentils, grains, and vegetables contains all
of the essential amino acids. Animal products are high in
protein, but are undesirable because of their high fat and
cholesterol content. Fat and cholesterol promote heart
disease, cancer, and many other health problems. One can
easily meet the body's protein requirements with plant foods.
It used to be believed that various plant foods had to be
eaten together to get their full protein value, but many
nutrition authorities, including the American Dietetic
Association, have determined that intentional combining is not
necessary.1 As long as one's diet includes a variety of
grains, legumes, and vegetables, protein needs are easily met.