November 16, 2009 / 12:04 AM / 9 years ago

Exercising in the heat may help you eat less: study

SYDNEY (Reuters Life!) - Exercisers trying to cut down on calories might want to take a run in the sun instead of a climate-controlled gym, according to a small Australian study.

The study of 11 physically active men found that participants ate less immediately after working out in hot conditions — about 97 degrees Fahrenheit (36 Celsius) — than in a more moderate, 77 degree Fahrenheit (25 degrees Celsius) environment.

On average, the men ate roughly 300 calories more when they worked out in moderate temperatures than when they exercised in the heat.

“Our findings suggest that if you exercise in a warmer environment you will eat less in the subsequent meal,” researcher Dr. Kym Guelfi, of the University of Western Australia’s School of Sports Science, told Reuters Health.

In theory, she said, that would be a good strategy for exercisers trying to lose weight. However, Guelfi added, future studies should look at whether warm-weather exercisers just make up for the smaller meals with larger ones later in the day.

For the study, which is published in the American Journal of Clinical Nutrition, the researchers had 11 young, regularly active men make several visits to the exercise lab.

During one visit, the men ran on a treadmill for 40 minutes in 97 degree heat; on another visit, they performed the same workout under 77 degree conditions. On a third visit, they rested in a moderately warm room.

In all three situations, the men were then presented with an all-you-can-eat breakfast buffet and were found to eat the most after working out in moderate conditions.

The study also found clues as to why exercising in the heat may dull appetite. After the hot workout, the men typically showed higher blood levels of peptide YY, a hormone produced in the digestive tract that serves a “fullness” signal.

The men’s smaller appetites also appeared to be related to the increases in core body temperature that came with the hot workouts.

The reasons for this are not clear, but Guelfi noted that some researchers believe that, because eating produces heat in the body, food intake is one of our natural mechanisms for controlling body temperature.

“This is why, anecdotally, cold environments have been said to lead to an increase in appetite,” she said.

But while a warmer environment may help curb post-exercise appetites, Guelfi cautioned against taking that idea to extremes.

“Exercise should not be performed in overly hot environments due to the risk of dehydration and heat illness,” she said.

Reporting by Amy Norton of Reuters Health, Editing by Belinda Goldsmith

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