Do I have a slow metabolism?

Q. No matter how much I cut calories, I can't lose weight. Could I have a slow metabolism?

A. People's bodies do respond very differently when they cut calories. A small study suggests why some people hold on to weight when they eat less, while others shed the pounds easily.

The study of 12 obese men and women took place in a laboratory. For the first three weeks, people were given enough calories to maintain weight. During this time, however, each person spent a total of four days either fasting or getting fed twice the normal amount. They spent these days in a chamber that measured their use of energy (metabolism).

As expected, all of the people in the study expended less energy during the fast. But some of them had a bigger decrease in energy use than others did.

During the overfeeding phase, everyone burned more calories. Again, this happens to all of us. Interestingly, the same people that used less energy during the fast also had a smaller increase in energy use when overfed.

Overall, their bodies conserved energy. Rather than slow metabolism, the researchers called it "thrifty metabolism."

After the steady-weight phase, everyone went on a low-calorie diet for six weeks. Each study participant was restricted to only 50% of the calories they needed to maintain weight.

In the last two weeks of the study, they went back to the steady-weight diet. During the calorie-cutting phase, people in the "thrifty metabolism" group lost less weight than others. People with "faster" metabolism lost more weight.

If you have a thrifty metabolism, losing weight will be a greater challenge for you. The formula of fewer calories and more exercise still works, but you might need to push it harder than you expected.

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