NEW YORK (Reuters Life!) - People with extra body fat may not have a lower core body temperature than thinner folks, according to a study -- contradicting one theory on what could lead some people to gain more weight.
The idea stems from the fact that a cooler core body temperature would mean there is less heat to shed and thus fewer calories being burned, which animal research has suggested could be the case.
"Temperature could be a marker for the 'slow metabolism' some people think they have," said Jack Yanovski, a senior researcher at the U.S. National Institute of Child Health and Human Development, who took part in the study.
Past research has found that genetically altered obese mice have a lower core temperature -- along with a slower than normal metabolism and bigger appetite.
But Yanovski said that he and his colleagues found no evidence that this is the case in humans in their study, reported in the American Journal of Clinical Nutrition.
In one experiment among several comparing the average core temperature of a group of obese adults with that of thinner men and women, 46 obese and 35 normal-weight or overweight adults swallowed wireless, temperature-sensing capsules to keep track of their core temperature for 24 hours.
On average, there was no difference in the two groups' core temperatures, with both around 36.9 degrees C (98.4 F).
In another experiment, the capsules were used to measure core temperature in 19 obese and 11 normal-weight people for 48 hours, while the participants kept a record of their daily activities.
Again, the two groups were similar, with no clear differences in body-temperature fluctuations throughout the day.
"For most obese individuals, it's not that they're just cooler inside," Yanovski said.
But there may be certain people for whom a lower core temperature has some impact on weight, and studies of people with alterations in genes that regulate core temperature could offer more insight into whether body temperature has a role in a risk for obesity, he added.
Reporting by Amy Norton at Reuters Health;editing by Elaine Lies