ROCHESTER, MINN. -- Some people seem able to eat whatever they want and not gain weight. The reason, says a Mayo Clinic study in the January 8 issue of Science, is that they burn hundreds of extra calories in the activities of daily living when they overeat.
Mayo Clinic researchers had 16 people overeat for two months and tracked what happened to the food the participants consumed, in terms of whether it was burned or stored as fat or other tissue.
They found that the key factor in predicting fat gain was the change in calories burned during the normal activities of daily living -- fidgeting, moving around, changing posture, etc. They labeled this factor NEAT (for non-exercise activity thermogenesis).
"Those people who had the greatest increase in NEAT gained the least fat, and those who had the least change gained the most," says James Levine, M.D., a Mayo Clinic endocrinologist. Dr. Levine, Michael Jensen, M.D., and Norman Eberhardt, Ph.D., of Mayo Clinic's Endocrine Research Unit were the authors of the report.
"When people overeat, NEAT switches on in some people to 'waste' this excess energy," says Dr. Jensen. "Conversely, the failure to switch this on allows the calories to be stored as fat. This study suggests that efforts to activate NEAT, perhaps through behavioral cues, may help prevent obesity."
Fat gain occurs when the energy (calories) taken in exceeds the energy burned. The three main factors involved in the burning of calories are
* Basal metabolic rate (BMR) -- burning of energy when the body is at rest
* Postprandial thermogenesis -- energy burned in the digestion, absorption and storage of food in the body
* Physical activity -- comprising exercise (sports and fitness activities) and NEAT
The researchers measured the contributions of each of these factors in the participants' total daily energy expenditure. For the first two weeks of the study, participants were fed so as to establish the dietary intake necessary to maintain a stable body weight. For the next eight weeks, they were fed an additional 1000 calories (equivalent to two Big Mac hamburgers) daily. Participants were limited to low levels of exercise, which was monitored.
Using sophisticated techniques, they were able to precisely measure the fate of the additional 1000 calories in each subject. Overall, they found:
Fate of Extra 1,000 Calories
* Deposited as fat 39 %
* Deposited as other body tissue 4 %
* Burned by BMR 8 %
* Postprandial thermogenesis 14 %
* Burned by NEAT 33 %
The 16 volunteers gained an average of 10 pounds in the two months of the study. However, weight gain varied from 2 pounds to almost 16 pounds. Those with the greatest increase in NEAT (the most was 692 calories per day) gained the least amount of fat.
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