Aside from the minimum amount of protein needed to keep the body running, there’s little guidance on the ideal amount of dietary protein or the healthiest proportion of calories contributed by protein. Country-to-country comparisons of protein intake and health aren’t much help because diets around the world tend to have similar amounts of protein. In the average American diet, which we tend to think of as meat-centered, about 15 percent of calories come from protein. In the largely vegetarian, rice-based diets that are common throughout Asia, about 12 percent of calories come from protein. (Rice, which we think of as a carbohydrate, is about 8 percent protein.) Other types of human studies haven’t paid that much attention to protein. Diet fads further confuse the issue, with competing claims for high-protein, low-carbohydrate diets and low-protein, high-carbohydrate diets.
Until there’s a good reason to change, getting 7 to 8 grams of protein per 20 pounds of body weight is a good guide for most people, but I don’t recommend that you count and track your daily grams of protein.
PROTEIN AND HUMAN HEALTH
The amount and type of protein in the diet has been linked at one time or another with chronic diseases such as cancer and heart disease. It may also influence diabetes in children, obesity, and gastrointestinal disorders. Specific proteins in food, the air, and elsewhere are responsible for a variety of allergies, although this book doesn’t cover that topic in detail.
Dietary Sources of Protein
* * *
Food
Serving Size
Calories
Protein (grams)
Protein % Daily Value*
Beef, top sirloin, broiled
3 ounces
155
26
52
Chicken, roasted
3 ounces
162
25
50
Salmon, fillet, cooked
3 ounces
130
21
42
Hamburger patty, 90% lean
3 ounces
178
21
42
Yogurt, Greek, low-fat
7-ounce container
146
20
40
Tuna, water-packed
3 ounces
73
17
34
Soy milk
1 cup
140
11
22
Soybeans, cooked
1/2 cup
127
11
22
Peanuts, dry-roasted
11/2 ounces
242
10.5
21
Cottage cheese, low-fat
3 ounces
69
9
18
Lentils, cooked
1/2 cup
115
9
18
Cheese pizza
1 slice
181
8
16
Milk, skim
1 cup
102
8
16
Black beans
1/2 cup
114
8
16
Whole milk
1 cup
149
8
16
Almonds
11/2 ounces
254
8
16
Whole wheat bread
2 slices
161
8
16
Tofu, firm
3 ounces
65
7.5
15
Cheddar cheese
1 ounce
115
7
14
Macaroni, cooked
1 cup
190
7
14
Egg
1 large
90
6
12
Walnuts
11/2 ounces
270
6
12
Brown rice, cooked
1 cup
248
5
10
Baked potato, flesh and skin
1 medium
161
4
8
Corn, cooked
1 medium ear
99
4
8
Broccoli, cooked
1/2 cup chopped
27
2
4
*Based on a daily value of 50 grams of protein per a 2,000-calorie daily diet
Source: USDA National Nutrient Database for Standard Reference, Release 28, 2016. ndb.nal.usda.gov/ndb/foods.
Protein and cancer. There’s no good evidence that eating a little or a lot of protein influences the risk of cancer in humans. You may have heard about low cancer rates in China or Japan, where the average diet contains a bit less protein—and certainly less animal protein—than the average American diet. In reality, though, total cancer rates in these countries have traditionally been about the same as they are in the United States, although the types of cancers that are the most common in each country are different.
Among more than 130,000 men and women in the Harvard Nurses’ Study and Health Professionals Follow-Up Study who were followed for up to thirty-two years, protein intake wasn’t linked to total deaths from cancer.2
The source of protein may make a difference. The International Agency for Research on Cancer, part of the World Health Organization, has concluded that processed meat is “carcinogenic to humans,” while red meat is “probably carcinogenic.”3 The link between processed meat consumption and cancer is mainly with colorectal cancer, but connections were also seen between consumption of processed and red meat and pancreatic and prostate cancer.
Age may also make a difference. Most studies have looked at diet during adulthood. It is possible that the seeds of cancer may be planted earlier. Recent analyses in the Nurses’ Health Study have found that higher intake of red meat during adolescence was associated with an increased risk of premenopausal breast cancer, while higher intakes of poultry, nuts, and legumes were associated with lower risks.4
Protein and heart disease. Country-to-country surveys of protein consumption and heart disease hint that the more plant protein in the diet, the less heart disease, and the more animal protein, the more heart disease. But different dietary and lifestyle habits in each of these countries—things like consumption of saturated fat, smoking rates, and amount of physical activity—make such surveys difficult to interpret. In the relatively few prospective studies of protein and heart disease, the source of protein makes a difference. In an analysis my colleagues and I did among more than 43,000 men, intake of total protein was minimally associated with heart disease risk, while intake of protein from meat was associated with higher risk.5 A slightly lower risk of heart disease was inconsistent: getting more protein from plants, or from poultry and fish, is linked to lower risk of heart disease, while getting more protein from meat, especially red meat, is related to higher risk.
Protein and diabetes. The source of dietary protein has important implications for type 2 diabetes too. Eating more red meat increases the risk of developing this chronic condition, while eating more nuts, legumes, and poultry is related to lower risk.
One or more proteins found in cow’s milk may—and I stress the “may”—play a role in the development of type 1 diabetes in children, one reason why infants should consume mother’s breast milk rather than cow’s milk if possible.
Premature death. In a large analysis of the dietary habits of women and men in the Harvard cohorts led by my colleague Mingyang Song, eating more protein from meat was linked with a modestly higher risk of premature death, while eating more protein from plant sources was associated with a lower risk. Similar findings were seen in a prospec
tive study of women living in Iowa.6
Protein and other chronic diseases. The medical literature is full of reports linking allergic responses to specific protein sources with conditions ranging from arthritis and breathing problems to chronic digestive disorders. Eggs, fish, milk, peanuts, tree nuts, and soybeans cause allergic reactions in some people. A startling and well-documented report published in the New England Journal of Medicine, for example, showed that something in cow’s milk causes an allergic response leading to severe chronic constipation in some young children.7 In a group of sixty-five toddlers with chronic constipation, two weeks’ worth of soy milk in place of cow’s milk cleared up the problem in two-thirds of the children. A return to cow’s milk led to the return of constipation. What’s more, the “responders” were also more likely to have had constant runny noses, bronchospasm, and skin inflammation when drinking cow’s milk. This may be a sentinel report pointing the way to other links between specific proteins and chronic disease.
Gluten, a mixture of proteins found mainly in wheat, rye, and barley, triggers a mistaken immune response in people with celiac disease (see “Gluten in Grains: A Danger for Some” on page 130). For some reason the immune response recognizes gluten as a foreign invader and attacks it. This attack damages the lining of the small intestine. People with celiac disease can’t tolerate any gluten. Even a little bit of it, say from a few crumbs of bread, is enough to cause problems.
Protein and weight control. As I described in chapter six, a diet higher in fat and protein and lower in carbohydrates tends to work better than a low-fat, high-carbohydrate diet for helping people shed pounds quickly. There are two reasons for this: First, chicken, beef, fish, beans, and other high-protein foods slow the movement of nutrients from the stomach to the small intestine. Slower stomach emptying means you feel full for longer. Second, protein’s rather gentle, steady effect on blood sugar avoids the quick, steep rise and fall in blood sugar caused by a carbohydrate like white bread or baked potato.
Once again, the protein package matters. In a detailed analysis of long-term weight change among the participants of the Harvard Nurses’ Health Study and Health Professionals Follow-Up Study cohorts, eating red meat, chicken with skin, and regular cheese was associated with greater weight gain, while eating yogurt, peanut butter, walnuts and other nuts, chicken without skin, low-fat cheese, and seafood was associated with less weight gain.8
Protein and bone health. Early research raised the theoretical problem that eating a lot of protein could be bad for bones. The digestion of protein releases acids into the bloodstream. At normal levels of protein intake, calcium and other agents in the blood neutralize these acids. With a high-protein diet, however, extra calcium is needed to neutralize these acids. Some experts worried that this neutralizing calcium would be pulled from bone. According to a systematic review of sixty-one studies, that doesn’t appear to happen.9
PAY ATTENTION TO THE PACKAGE
Pure protein from meat probably has about the same effect on your health as pure protein from beans or nuts. As I have mentioned before, it’s the protein package—what comes along with the protein, like healthful or harmful fats, beneficial fiber, or hidden salt—that makes a substantial difference in health.
Beef is a good source of complete animal protein. But it also delivers a lot of saturated fat. The same is true for whole milk or dairy foods made from whole milk, such as butter, ice cream, and cheese. Poultry and nuts are good sources of protein, but unlike red meat or beef they also deliver healthy unsaturated fats.
There’s more to the protein package than fats. People who regularly eat hot dogs, bologna, bacon, and other processed meats are more likely to develop type 2 diabetes and colon cancer than those who don’t. That may be due to the salt, nitrates, and other additives these products contain. Men whose diets include a lot of dairy foods seem to be more likely to develop prostate cancer, especially quickly spreading (metastatic) prostate cancer, than men who don’t often eat dairy foods.11 Dairy foods increase the blood level of insulin-like growth factor 1, which in turn is related to higher risk of prostate cancer.
Go Nuts
* * *
The next time you’re racking your brain over what to have for a snack or to make for dinner, think about using nuts as part of the main dish or as a garnish. Your taste buds and your heart will thank you.
Some people think that nuts are “junk food.” Nothing could be further from the truth. They’re a great source of protein and other beneficial nutrients. An ounce of almonds, walnuts, peanuts, or pistachios gives you about 8 grams of protein, the same as a glass of milk. It’s true that nuts contain quite a bit of fat, but this is mostly healthy unsaturated fat that reduces harmful LDL cholesterol and keeps protective HDL cholesterol high.
People who regularly eat nuts are less likely to have heart attacks or die from heart disease than those who rarely eat them. Several large cohort studies, including the Adventist Health Studies, the Iowa Women’s Health Study, and the Nurses’ Health Study, have shown a consistent 30 to 50 percent lower risk of heart attack or heart disease associated with eating nuts several times a week. Regularly including nuts in the diet also seems to help prevent type 2 diabetes and gallstones.
The value of eating nuts was documented in the PREDIMED trial (see page 96). In this five-year trial, participants who were asked to eat an ounce of nuts each day in addition to a Mediterranean diet had lower risk of heart disease than those who followed a low-fat diet.10 Notably, the nut eaters did not gain more weight than those on the low-fat diet.
The evidence for the health benefits of nuts is strong enough that the FDA let food companies claim on nutrition labels that “eating 1.5 ounces per day of most nuts as part of a diet low in saturated fat and cholesterol may reduce the risk of heart disease.”
How do nuts benefit the heart? There are plenty of possibilities. Their unsaturated fats help lower harmful LDL cholesterol and boost protective HDL cholesterol. One type of unsaturated fat found in walnuts, the omega-3 fatty acid known as alpha-linolenic acid (ALA), seems to help prevent blood clots and potentially deadly erratic heartbeats (see “Omega-3 Fats: A Special Benefit” on pages 80–83). Nuts are also rich in arginine, an amino acid needed to make a tiny but important molecule called nitric oxide. Nitric oxide helps relax blood vessels and ease blood flow. It also makes blood platelets (tiny blood particles that are involved in clotting) less sticky and less likely to form clots in the bloodstream. Vitamin E, folic acid, potassium, fiber, and other phytonutrients found in nuts may also contribute to their heart-health benefits.
Whatever the mechanism, the message is the same: Nuts are good for your heart and the rest of you—if you eat them the right way.
Here’s the wrong way: eating nuts on top of your usual snacks and meals. At 160 calories an ounce, having a handful of almonds a day without cutting back on anything else could translate into adding 10 to 20 pounds over the course of a year. This extra weight would cancel out any benefit from nuts and tip the scales toward, not away from, heart disease.
Here’s the right way: eating nuts instead of chips or a candy bar as a snack. They’ll take the edge off hunger every bit as well as junk food, they taste as good as or better than junk food, and they give you healthy nutrients to boot.
Better yet, use nuts instead of meat in main dishes. Mediterranean and other traditional cuisines use nuts this way in all sorts of delicious dishes and sauces. For example, check out the delicious Roasted Walnut and Brown Rice Loaf on page 339.
Comparing protein packages
* * *
Food
Protein (grams)
Saturated fat (grams)
Monoun-saturated fat (grams)
Polyun-saturated fat (grams
ALA* (grams)
Marine**Omega-3 fats (grams)
Fiber (grams)
Sodium (milligrams)
Sirloin steak, broiled (4 oz)
33
4.6
4.9
0.4
0.4
0.
0
66
Sockeye salmon, grilled (4 oz)
30
1.1
2.1
1.5
0.3
1.0
0
104
Chicken, thigh, no skin (4-oz)
28
2.7
3.9
2.0
0.1
0.1
0
120
Ham steak (4 oz)
22
1.6
2.2
.5
.5
0
0
1,439
Lentils (1 cup cooked)
18
0.1
0.1
0.3
0.3
0
4
4
Milk (8 ounces)
8
3.1
1.4
0.2
0.3
0
0
115
Peanut butter (2 tbl)
7
3.3
8.3
4.0
0
0
1.6
136
Almonds, dry roasted, unsalted (1 oz)
6
1.2
9.4
3.4
0
0
3.1
1
* Alpha-linoleic acid. Small amounts of other 18:3 omega-3 fatty acids are included.
** Mainly EPA and DHA.
Source: USDA National Nutrient Database for Standard Reference Release 28, 2016.ndb.nal.usda.gov/ndb/foods
How meat is prepared may also contribute to its effects on health. Frying and grilling meat, poultry, and fish to a well-done degree causes some of the protein to turn into a group of chemicals called heterocyclic amines that cause cancer in animals. How much this increases cancer risk in humans hasn’t been clearly determined.
Eat, Drink, and Be Healthy Page 18