BEIJING, China — Is exercise actually hurting the amount of fat overweight people burn? Scientists from the Shenzhen Institute of Advanced Technology (SIAT) of the Chinese Academy of Sciences and the University of Roehampton report that exercise reduces the amount of calories obese individuals burn while at rest.
Exercise typically help people burn more calories, but these findings indicate it isn’t so simple for those with excess weight. Study authors conclude that regular exercisers of all sizes tend to get fewer calorie-burning benefits out of their workouts than they think. This decline in calories burned at rest, however, is much worse among obese individuals and older adults as well.
An analysis of 1,750 people showed that among those with the highest BMI (including those who classify as obese), only 51 percent of calories burned during exercise ultimately translated into calories burned at the end of the day. For those with a normal BMI, that number was a much healthier 72 percent.
“When enrolled into exercise programs for weight loss, most people lose a little weight. Some individuals lose lots, but a few unlucky individuals actually gain weight,” says corresponding study co-author Prof. John Speakman from SIAT in a media release.
‘People with obesity efficient at hanging onto their fat stores’
Researchers speculate these calorie-burning fluctuations between individuals are likely due to “compensatory mechanisms.” Examples of compensatory mechanisms include eating more because a workout stimulates one’s appetite or reduced energy expenditure on resting metabolism — which would make exercise less costly from an energy perspective.
“But we wanted to find out why some people show such compensatory mechanisms and others don’t,” explains lead study author Prof. Lewis Halsey from the University of Roehampton.
The ensuing analysis led to the discovery of two factors dominating how much people compensate for burning calories. One is age: older adults tend to compensate more. The second is obesity: these individuals tend to reduce their resting metabolism when they are more physically active.
For those with obesity, the end result is that for every calorie spent on exercise, the body saves half a calorie while resting. All in all, the research team call their findings a cruel twist for obese individuals trying to lose weight. It will likely be much harder for them to shed excess pounds simply by exercising more.
“Around the world, national guidelines tend to recommend a 500–600 calorie deficit through exercising and dieting to lose weight. However, they do not take into account the reduction of calories being burned in the most basic of human functions as the body compensates for the calories burned on the exercise,” Prof. Halsey adds.
“This analysis using data from the DLW database shows how individuals are not all the same in the way they budget their energy use. People living with obesity may be particularly efficient at hanging onto their fat stores, making weight loss difficult,” Prof. Speakman concludes.
The study is published in Current Biology.