Q. How does body temperature affect metabolism

and weight?

A. Maintaining a constant body temperature takes energy, but it’s not yet clear whether that affects your weight. Lewis Landsberg, director of the Northwestern University Comprehensive Center on Obesity, says it makes sense that people with slightly lower than normal body temperatures expend less energy and require fewer calories than those with higher ones, and so may tend to gain weight more easily. But in a recent study of 12 lean and 12 obese individuals, he and colleagues did not find evidence that obese people were more likely to have lower body temperatures.

External temperatures can affect metabolism through “brown fat,’’ a type of fat tissue recently discovered in adults. Activated by the cold, brown fat burns calories to generate heat and seems to be more abundant in lean people. A recent study in the Journal of Clinical Investigation found that keeping a small group of men in chilly temperatures caused their brown fat to burn energy and raised their overall energy expenditure. A paper published last year in Obesity Reviews argued that rising indoor air temperatures combined with less time spent outdoors may be contributing to the rise in obesity by causing us to use less energy heating our own bodies and activating our brown fat less. More study is needed.

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