Until recently, protein got little attention. Like a quiet child in a
classroom of rowdies, it was often overshadowed by fat, carbohydrates, and
vitamins. That's changing. Lately there's been an explosion of interest in protein,
largely triggered by high-protein diets for weight loss.
Surprisingly little is known about protein and health. The Institute of Medicine
recommends that adults get a minimum of 0.8 grams of protein for every kilogram
of body weight per day to keep from slowly breaking down their own tissues (1).
That's just about 8 grams of protein for every 20 pounds of body weight. Beyond
that, there's relatively little solid information on the ideal amount of
protein in the diet, a healthy target for calories contributed by protein, or
the best kinds of protein.
Q. How much protein do I need each day?
A. There is no one-size-fits-all answer to that question,
and research on the topic is still emerging.
Around the world, millions of people don't get enough protein. Protein
malnutrition leads to the condition known as kwashiorkor. Lack of protein can
cause growth failure, loss of muscle mass, decreased immunity, weakening of the
heart and respiratory system, and death.
In the United States
and other developed countries, getting the minimum daily requirement of protein
is easy. Cereal with milk for breakfast, a peanut butter and jelly sandwich for
lunch, and a piece of fish with a side of beans for dinner adds up to about 70
grams of protein, plenty for the average adult.
All Protein Isn't Alike
Some of the protein you eat contains all the amino acids needed to build new
proteins. This kind is called complete protein. Animal sources of protein tend
to be complete. Other protein sources lack one or more "essential"
amino acids—that is, amino acids that the body can't make from scratch or
create by modifying another amino acid. Called incomplete proteins, these
usually come from fruits, vegetables, grains, and nuts.
Vegetarians need to be aware of this. To get all the amino acids needed to
make new protein—and thus to keep the body's systems in good shape—people who
don't eat meat, fish, poultry, eggs, or dairy products should eat a variety of
protein-containing foods each day.
The Protein Package
What Is Protein?
Protein is found throughout the body—in muscle, bone, skin,
hair, and virtually every other body part or tissue. It makes up the enzymes
that power many chemical reactions and the hemoglobin that carries oxygen in
your blood. At least 10,000 different proteins make you what you are and keep
you that way.
Twenty or so basic building blocks, called amino acids,
provide the raw material for all proteins. Following genetic instructions, the
body strings together amino acids. Some genes call for short chains of amino acids;
others are blueprints for long chains that fold, origami-like, into intricate,
Because the body doesn't store amino acids, as it does fats
or carbohydrates, it needs a daily supply of amino acids to make new protein.
Animal protein and vegetable protein probably have the same effects on
health. It's the protein package that's likely to make a difference.
A 6-ounce broiled porterhouse steak is a great source of complete protein—38
grams worth. But it also delivers 44 grams of fat, 16 of them saturated. (2)
That's almost three-fourths of the recommended daily intake for saturated fat.
The same amount of salmon gives you 34 grams of protein and 18 grams of fat, 4
of them saturated. (2) A cup of cooked lentils has 18 grams of protein, but less
than 1 gram of fat. (2)
The bottom line is that it's important to pay attention to what comes along
with the protein in your food choices. Vegetable sources of protein, such as
beans, nuts, and whole grains, are excellent choices, and they offer healthy
fiber, vitamins, and minerals. Nuts are also a great source of healthy fat.
The best animal protein choices are fish and poultry. If you are partial to
red meat, such as beef, pork, or lamb, stick with the leanest cuts, choose
moderate portion sizes, and make it only an occasional part of your diet, for
several reasons: A major report on cancer prevention recommends consuming less
than 18 ounces a week of red meat and avoiding processed meats (such as hot
dogs, bacon, or ham) to lower the risk of colon cancer. (3) There's
also substantial evidence that replacing red meat with fish, poultry,
beans, or nuts, could help prevent heart disease, and that lowering red meat
can lower the risk of diabetes. (30, 31) Processed meats, especially, have been
most strongly linked with cardiovascular disease and diabetes, at least in part
due to their high added sodium content. (Learn more about why cutting
salt and sodium is good for your health, and learn what you can do to lower
your risk of type 2 diabetes.)
Protein and Chronic Disease
The most solid connection between protein and health has to do with
allergies. Proteins in food and the environment are responsible for these
overreactions of the immune system. Beyond that, relatively little evidence has
been gathered regarding the effect of protein on the development of chronic
Cardiovascular disease: One concern about the high-protein
diet craze has been that eating diets high in protein and fat, and low in
carbohydrate, would harm the heart. Recent research provides reassurance that
eating a lot of protein doesn't harm the heart.
Many people think of nuts as just another junk food snack.
In reality, nuts are excellent sources of protein and other healthful
nutrients. Learn why nuts are healthy for the heart.
In fact, it is possible that eating more protein, especially vegetable
protein, while cutting back on easily digested carbohydrates may benefit the
heart. A 20-year prospective study of 82,802 women found that those who ate
low-carbohydrate diets that were high in vegetable sources of fat or protein
had a 30 percent lower risk of heart disease, compared to women who ate
high-carbohydrate, low-fat diets. (4) But women who ate low-carbohydrate diets
that were high in animal fats or proteins did not have a reduced risk of heart
Diabetes: Although proteins found in cow's milk have been
implicated in the development of type 1 diabetes (formerly called juvenile or
insulin-dependent diabetes), ongoing research has yielded inconsistent results.
(5) The amount of protein in the diet doesn't seem to adversely affect the
development of type 2 diabetes (formerly called adult-onset diabetes), although
research in this area is ongoing. A recent 20-year prospective study in women
suggests that eating a low-carbohydrate diet that is high in vegetable sources
of fat and protein may modestly reduce the risk of type 2 diabetes.(26)
Cancer: There's no good evidence that eating a little
protein or a lot of it influences cancer risk. Eating a lot of red meat is
linked to an increased risk of colon cancer, however, as is eating processed
Osteoporosis: Digesting protein releases acids that the
body usually neutralizes with calcium and other buffering agents in the blood.
Eating lots of protein, such as the amounts recommended in the so-called
low-carb or no-carb diets, takes lots of calcium. Some of this may be pulled
from bone. Following a high-protein diet for a few weeks probably won't have
much effect on bone strength. Doing it for a long time, though, could weaken
bone. In the Nurses' Health Study, for example, women who ate more than 95
grams of protein a day were 20 percent more likely to have broken a wrist over
a 12-year period when compared with those who ate an average amount of protein
(less than 68 grams a day). (6) But this area of research is still
controversial, and findings have not been consistent. Some studies suggest
increasing protein increases risk of fractures; others associate high-protein
diets with increased bone -mineral density. The evidence is inconclusive, and
more research is needed.
Protein and Weight Control
The notion that you could lose weight by cutting out carbohydrates and
eating plenty of protein was once tut-tutted by the medical establishment,
partly because such diets were based on little more than interesting ideas and
speculation. In the past few years, head-to-head trials that pitted
high-protein, low-carbohydrate diets against low-fat, high-carbohydrate diets
have provided some evidence that a low-carbohydrate diet may help people lose
weight more quickly than a low-fat diet, although so far, that evidence is
In two short, head-to-head trials, low-carb approaches worked better than
low-fat diets. (7, 8) A more-recent year-long study, published in 2007 in the Journal
of the American Medical Association, showed the same thing. (9) In this
study, overweight, premenopausal women went on one of four diets: Atkins, Zone,
Ornish, or LEARN, a standard low-fat, moderately high-carbohydrate diet. The
women in all four groups steadily lost weight for the first six months, with
the most rapid weight loss occurring among the Atkins dieters. After that, most
of the women started to regain weight. At the end of a year, it looked as
though the women in the Atkins group had lost the most weight since the start
of the study, about 10 pounds, compared with a loss of almost 6 pounds for the
LEARN group, 5 pounds for the Ornish group, and 3½ pounds for the Zone group.
Levels of harmful LDL, protective HDL, and other blood lipids were at least as
good among women on the Atkins diet as those on the low-fat diet.
If you read the fine print of the study, though, it turns out that few of
the women actually stuck with their assigned diets. Those on the Atkins diet
were supposed to limit their carbohydrate intake to 50 grams a day, but they
took in almost triple that amount. The Ornish dieters were supposed to limit
their fat intake to under 10 percent of their daily calories, but they got
about 30 percent from fat. There were similar deviations for the Zone and LEARN
What about longer term studies? POUNDS LOST (Preventing Overweight Using
Novel Dietary Strategies), a two-year head-to-head trial comparing different weight
loss strategies found that low-carb, low-fat, and Mediterranean-style diets
worked equally well in the long run, and that there was no speed advantage for
one diet over another. (27) What this and other diet comparisons tell us is
that sticking with a diet is more important than the diet itself. (Read more
about the POUNDS LOST weight loss trial.)
Why, in some studies, do high-protein, low-carb diets seem to work more
quickly than low-fat, high-carbohydrate diets, at least in the short run?
First, chicken, beef, fish, beans, or other high-protein foods slow the
movement of food from the stomach to the intestine. Slower stomach emptying
means you feel full for longer and get hungrier later. Second, protein's
gentle, steady effect on blood sugar avoids the quick, steep rise in blood
sugar and just as quick hunger-bell-ringing fall that occurs after eating a
rapidly digested carbohydrate, like white bread or baked potato. Third, the
body uses more energy to digest protein than it does to digest fat or
No one knows the long-term effects of eating
high-protein diets with little or no carbohydrates. Equally worrisome is the
inclusion of unhealthy fats in some of these diets. There's no need to go
overboard on protein and eat it to the exclusion of everything else. Avoiding
fruits and whole grains means missing out on healthful fiber, vitamins,
minerals, and other phytonutrients. It's also important to pay attention to
what accompanies protein. Choosing plant-based high-protein foods that are low
in saturated fat will help the heart even as it helps the waistline.