Women Lag Cookie a Day in Weight Loss : Health: Study finds that females burn fat more slowly than males, roughly by the equivalent of one chocolate chip cookie each 24 hours.

Women run more to fat than men do, and a new study offers a possible reason--females burn fat more slowly, at a rate equivalent to a chocolate chip cookie a day.

The analysis of data on 194 women and 328 men looked at the resting metabolic rate, the rate at which you burn calories as you lie in bed right after you wake up. It’s the amount of calories your body burns just to keep itself alive.

The study finds that, after other factors are taken into consideration, the resting metabolic rate of women is 3% lower than in men.

“That’s about 50 calories per day, like a chocolate chip cookie,” said researcher Eric T. Poehlman of the Baltimore Veterans Affairs Medical Center. His study is in the American Physiological Society’s Journal of Applied Physiology.

Three percent may not seem to be a lot, but it adds up “over the period of a lifetime,” Poehlman said. Exercise is a good way to burn off the caloric difference. Exercise can increase metabolic rate 15- to 20-fold, which would “eat up that cookie and then some,” he said.

Other metabolic differences between men and women are larger than the one he and his colleagues found in the base rate, Poehlman said. For instance, men have proportionately more muscle than women, and muscle cells burn calories faster than fat cells. Also, he said, men tend to be bigger than women, and larger bodies tend to burn more calories.

The overall resting metabolic rate of the women was 1,348 calories a day, while the rate for men was 23% higher, the report said.

The researchers compared men and women at the same fitness levels and with the same proportion of fat and muscle, Poehlman said.

The subjects took a treadmill test to determine how fit they were. The amount of fat on their bodies was estimated by underwater weighing, a technique based on the principle that fat is lighter than muscle in water.

All women were tested at the same point in their menstrual cycles, because metabolic rate varies at different points in the cycle, Poehlman said. Exercisers were tested 36 to 48 hours after the last time they worked out, so any residual metabolic increase caused by exercise would have spent itself.

The volunteer participants, who ranged in age from about 17 to 81, slept at the test center and were tested in the morning. Their resting metabolic rates were measured by the proportion of carbon dioxide, a product of metabolism, as they exhaled.

The large number of participants, 522, gives the study added authority, Poehlman said. Larger total numbers make the study’s averages less likely to be skewed by unusual differences in individuals, and so make the finding of a small average difference more likely to be valid.

The study does not explain the reason for the approximate 50-calorie gap between the sexes. One possibility is that women are more likely than men to diet, and restrictions on calories taken in trigger the body to compensate by lowering the rate it uses calories up, Poehlman said.

Another researcher has an alternative possible explanation.

Women could have a lower metabolic rate because they carry more fat around the buttocks and thighs than men do, and fat in these areas is less metabolically active, said Rudy Dressendorfer of New Mexico Highlands University in Las Vegas, N.M.

But Dressendorfer does not consider the study’s finding conclusive.

The formulas used in underwater weighing don’t distinguish between men and women, because most of the bodies used to develop the formulas were male, Dressendorfer said. If women have more muscle than the formulas supposed, then researchers could have underestimated metabolic rates, he said.

Another researcher says the study seems to have been carefully done, and the findings could be important in weight control. But Jack H. Wilmore of the University of Texas wants to see other scientists duplicate the work to make sure the findings hold up.