Harvard Men's Health Watch

Good nutrition: Should guidelines differ for men and women?

In the stereotypical Ozzie and Harriet family of the 1950s, men ruled the roost while women ruled the roast. That's no longer true (if it ever was), but in most households women are still in charge of nutrition. They stock the pantry, plan the menus, and fill the plates. In most households it's a good thing, since the average woman knows more about nutrition than the average man. But when it comes to optimal nutrition, there are differences between the sexes. The differences are subtle, but they may affect a man's health.

Here is a quick summary of the similarities and differences in dietary guidelines for men and women.

Calories

Men and women are 98.5% identical in their DNA, and their nutritional needs are more similar than different. That's certainly true of calories; in this case, at least, men act just like big women.

A person's caloric requirement depends on his body size and exercise level. Sedentary people of both genders will keep their weight stable by taking in about 13 calories per pound of body weight each day. Moderate physical activity boosts this requirement to 16 calories a pound, and vigorous exercise calls for about 18 calories a pound. On average, a moderately active 125-pound woman needs 2,000 calories a day; a 175-pound guy with a similar exercise pattern needs 2,800 calories. And like women, men will lose weight only if they burn more calories than they take in.

Protein

Here, too, body size is the main difference between the needs of males and females. Despite all the hype about high-protein diets, our protein requirements are really quite modest — only about a third of a gram per pound of body weight. For a 125-pound woman, that amounts to about 42 grams, for a 175-pound man, 58 grams. That's a tiny difference, just about half an ounce a day.

Protein should provide about 15% of a healthy person's daily calories. As a rule of thumb, people of both sexes and any size will do fine with about 60 grams of protein a day. Athletes who have large muscles and work out hard may need 20% more. But even that's not very much; 8 ounces of chicken or 6 ounces of canned tuna, for example, will fit the bill.

Most Americans get far more protein than they really need. In theory, that may not be wise. Like carbohydrates, protein provides 4 calories per gram, and excess calories from any source will be stored as body fat. Excess dietary protein increases calcium loss in the urine, perhaps raising the risk for osteoporosis ("thin bones," more a worry for women) and kidney stones (a particular worry for men).

Carbohydrates

Carbs are gender-neutral. But that doesn't mean you should be neutral about the carbohydrates you eat.

Carbohydrates should provide 45%–65% of your daily calories. Most of those calories should come from the complex carbohydrates in high-fiber and unrefined foods, such as bran cereal and other whole-grain products, brown rice, beans and other legumes, and many fruits and vegetables. These carbohydrates are digested and absorbed slowly, so they raise the blood sugar gradually and don't trigger a large release of insulin. People who eat lots of these foods have higher HDL ("good") cholesterol levels and a lower risk of obesity, diabetes, and heart disease. A good amount of soluble fiber in the diet lowers LDL ("bad") cholesterol, and high-fiber diets reduce the risk of intestinal disorders ranging from constipation and diverticulosis to hemorrhoids. Some studies have shown that fiber may help reduce the risk of colon cancer. Men need more fiber than women: 38 vs. 25 grams a day before the age of 50 and 30 vs. 21 grams a day thereafter.

Simple sugars are another matter; they really are empty calories. You should limit your sugar consumption to 10% of your daily calories; for the average person, that's about 60 grams or 12 teaspoons of table sugar.

Fat

It's an area of important differences as well as similarities. The fats on the "bad" list are the same for men and women, but the fats on the "good" list are not.

Both men and women should keep their total fat consumption below 30%–35% of daily calories. Since fat is the most calorie-dense food (9 calories per gram), levels as low as 20%–25% are appropriate when weight is an issue.

To achieve these goals, cut down on saturated fat from animal products (meat and the skin of poultry, whole-fat dairy products, and certain vegetable foods — palm oil, palm kernel oil, cocoa butter, and coconut). And it's just as important to reduce your consumption of trans fatty acids, the partially hydrogenated vegetable oils found in stick margarine, fried foods, and many commercially baked goods and snack foods.

Make up the difference by including more unsaturated fats in your diet. Monounsaturated fats are healthful for both men and women; olive oil is a good source. The two omega-3 fatty acids found in fish are highly desirable for both sexes. But the vegetable omega-3 is a different matter.

The problem omega-3 is alpha-linolenic acid (ALA). It is particularly abundant in canola oil and flaxseed oil. Like the marine omega-3s, ALA is good for the heart, but unlike fish oil, which may reduce the risk of prostate cancer, ALA may not be good for the prostate.

The best evidence that ALA can protect the heart comes from the Lyon Diet Heart Study, a randomized clinical trial in Europe. It tested the effects of an ALA-enriched Mediterranean diet in 605 patients with coronary artery disease. Over a four-year period, the high-ALA diet produced a 72% reduction in heart attacks and cardiac deaths and a 56% lower risk of dying from any cause (including cancer). The Mediterranean diet differed from the standard Western diet in many respects, but because it contained a special canola oil margarine, the greatest difference was in its ALA content, which was nearly eight times higher in the protective diet.

If a canola-rich Mediterranean diet seems exotic, consider that two Harvard studies found that American men and women whose diets were high in ALA had a lower risk of dying from cardiovascular disease than people with diets low in ALA. ALA also appears to protect against stroke.

Although canola oil appears to be good for the cardiovascular system, two Harvard studies have raised concerns that ALA might be bad for the prostate. In 1993, the Health Professionals Follow-up Study of 47,781 men published a major evaluation of dietary fat and prostate cancer. It found that saturated fat from animal sources such as red meat and whole-fat dairy products was linked to a 2.6-fold increase in prostate cancer. But the study also provided some disquieting news about ALA: Men who consumed the most ALA were 3.4 times more likely to be diagnosed with prostate cancer than those who had the lowest dietary intake.

A year later, a second Harvard study added to the concern. The Physicians' Health Study of 20,885 men did not evaluate diet per se, but it did measure the blood levels of ALA in 120 men who developed prostate cancer and compared them with the levels in 120 men who remained free of the disease. Men with moderately high ALA blood levels were 3.4 times more likely to develop prostate cancer than men with the lowest levels; curiously, though, men with the very highest levels were only 2 times more likely to get the disease.

The Harvard research from 1993 and 1994 prompted a number of similar investigations around the world. Four have supported a link between ALA and prostate cancer; three have not.

It's still an open question, but there is no question that ALA represents a dietary difference between the sexes. For women, it's a healthful fat. For men with heart disease or major cardiac risk factors, it may also be a good choice — but men with more reason to worry about prostate cancer should probably get their omega-3s from fish and their vegetable fats largely from olive oil.

Alcohol

There are gender differences here, too, but this time women face the dilemma.

In both men and women, low doses of alcohol appear to reduce the risk of heart attacks and certain strokes. For both, larger amounts increase the risk of many ills, including liver disease, high blood pressure, behavioral problems, and premature death.

Men who choose to drink and can do so responsibly may benefit from one to two drinks a day, counting 5 ounces of wine, 12 ounces of beer, or 1.5 ounces of spirits as one drink. But women face an extra risk: Even low doses of alcohol can raise their risk of breast cancer. So women who choose to drink might be wise to limit themselves to half as much as men.

Vitamins

For most vitamins, the Recommended Daily Allowance (RDA) is the same for men and women. But for some, body size is responsible for slight differences. In any case, a healthful diet will provide plenty of vitamins for everyone, and a daily multivitamin will provide some insurance along with vitamin D that can be hard to get from diet alone.

Calcium

Like motherhood and apple pie, it's almost an article of faith that a lot of calcium is good for you. That may be true for mothers and other women, but it may not be so true for fathers and other men.

Calcium is important for women; a high-calcium diet may help lower their risk of osteoporosis. Although it's less common, men can get osteoporosis, too; but there is much less evidence that dietary calcium is protective for men.

Calcium may even be harmful for men, at least in large amounts. The worry is prostate cancer, and two Harvard studies have raised the alarm. In 1998, the Health Professionals Follow-up Study found that a high consumption of calcium from food or supplements was linked to an increased risk of advanced prostate cancer. The risk was greatest in men who got more than 2,000 mg a day. More recently, the U.S. Physicians' Health Study reported that a high consumption of calcium from dairy products appeared to increase a man's risk of prostate cancer by up to 37%. A study from the Fred Hutchinson Cancer Research Center in Seattle also found a link between calcium and advanced prostate cancer.

What's a man to do? Fortunately, he does not have to choose between his bones and his prostate. The solution is moderation. The Baltimore Longitudinal Study of Aging, for example, found no link between a moderate consumption of calcium (about 800 mg a day, two-thirds of the RDA) and prostate cancer. In addition, a randomized clinical trial of calcium supplements of 1,200 mg a day found no effect on the prostate, but only 327 men were in the calcium group, and the supplementation lasted just four years. Finally, the Harvard scientists speculate that a high consumption of vitamin D may offset the possible risks of calcium, so a daily multivitamin may also help.

Iron

There's not much doubt about this one: Women need more iron than men, because they lose iron with each menstrual period. After menopause, of course, the gap closes. The RDA of iron for premenopausal women is 18 mg a day, for men 8 mg. Men should avoid excess iron. In the presence of an abnormal gene, it can lead to harmful deposits in various organs (hemochromatosis). Since red meat is the richest dietary source of iron, it's just as well that men don't need to wolf down lots of saturated fat to get a lot of iron.

Other minerals

The tiny gender differences in minerals other than calcium and iron depend on body size. But while the dietary requirements for selenium fit this rule, men may benefit from supplements of about 200 micrograms a day, a level about four times above the RDA. That's because both a clinical trial and an observational study suggest that selenium may reduce the risk of prostate cancer. It's far from proven, but it's something for men to consider.

You are what you eat

It's true for both men and women. And it's also true that a healthy, balanced diet is best for both genders. But there are differences; the fine print of nutrition is one more way that the sexes are opposite.