Women need fewer calories but more nutrients than men to be at their best. See how women's needs differ in part 1 of our two-part series.
According to the old nursery rhyme, little boys and little girls are made of very different things. While you can fault the rhyme for not being factually accurate, it does highlight an interesting point. In some respects, men and women have different nutritional needs, largely due to differences in male and female hormones.
But we don't start out all that differently, nutritionally speaking.
"If you look at the current federal dietary guidelines for kids, there is no difference in nutritional needs for males and females until age 9," says Elaine Turner, PhD, RD, associate professor in the department of Food Science and Human Nutrition at the University of Florida in Gainesville.
Once we hit puberty, however, she added, everything changes. And women's unique role as the bearers of children tends to drive their special nutritional needs.
Women Need Fewer Calories
"A woman and man of the exact weight and percentage of fat would burn the same amount of calories for the same amount of exercise," says Sharon B. Spalding, MEd, CSCS, professor of physical education and health at Mary Baldwin College in Staunton, Va. "However men are usually larger with a higher lean weight and will burn more calories."
Body composition comes into the picture, she says, because we know that muscle takes more calories to maintain -- even when you're not exercising -- than fat.
So women need fewer calories than men in part because they tend to be smaller and have higher fat percentages than men. That means women have to be choosier about what they eat. If you need fewer calories, the calories you take in need to pack a lot of nutritional punch.
In general, women need around 1,200 calories every day and men need a few hundred calories more. If you exercise you'll need much more depending on how active you are.
"Remember that to determine caloric expenditure one must take into consideration the intensity and duration of the activity, as well as the body weight of the person exercising," said Spalding.
More Iron, Please
For women of childbearing age, blood loss through menstruation can lead to iron deficiency. The Institute for Medicine of the National Academies recommends a daily allowance of 18 milligrams of iron for women aged 19 to 50. During pregnancy a woman's requirements are even greater. Men in that same age range need just 8 milligrams daily.
"Iron is one of the few things women need way more of than men," Spalding says.
Most men get all the iron that they need from the food they eat. For many women, it's often not so easy, because they have lower calorie needs.
"Women need to eat a diet rich in meat, fish, and poultry," says Spalding. "For vegetarian women it may be harder to get iron from dietary sources because the iron from plant foods is not absorbed as well."
According to the American Dietetic Association, most grain foods we eat, such as cereals, pasta, and bread, are now fortified with iron. Some foods that are naturally high in iron include spinach, chard, beans (pinto, kidney, black), lentils, and split peas.
And remember, Turner notes, "women can be iron deficient and not be anemic. Being iron deficient can keep women from performing optimally."
Calcium and Folate
Another area to watch is calcium.
"Women build bone into their mid-20s, and they need to eat calcium-rich foods to promote bone density," says Spalding. "More calcium may be needed for women in menopause since with estrogen declines, calcium may 'leak' from the bones."
The daily calcium recommendations are 1,000 milligrams a day for women under 50, and 1,500 milligrams a day for women 51 and older. Oddly enough, these are the same requirements for men, who are much less prone to osteoporosis than women. But the recommendation takes into account the fact that women are smaller than men. Thus the amount of daily calcium is greater for women on a proportional basis.
Both women and men need folate, or folic acid. At proper levels, it has been linked to better heart health and possible protection from colon cancer.
But for women in their childbearing years, getting enough of this B-vitamin can greatly reduce the chances of neurological birth defects. The Institute of Medicine recommends 400 micrograms daily for people over age 14. Pregnant women need 600 micrograms daily, and women who are breastfeeding need 500 micrograms daily.
"It's difficult to overstate the need for women to get sufficient folate before and during pregnancy," says Turner. "It's important for overall good health, but for the developing fetus, it can make all the difference in the world."
John Casey is a freelance writer in New York City.
Originally published Oct. 4, 2004.
Medically updated August 2006.