- In obese people, the effects of exercise are counterbalanced by less burning of calories at rest.
- For every calorie spent in exercise, they provide about half a calorie at rest.
- It is a compensatory effect that occurs when exercise reduces calorie expenditure when the metabolism is at rest. This allows the body to “save” its energy after physical exertion.
According to World Health Organization (WHO) guidelines, adults should get at least 150 minutes – or 2.5 hours – of moderate to vigorous physical activity per week. But while physical activity is essential to health and well-being, it can also be a double-edged sword, especially for obese people.
This is what a new study published August 27 in the journal shows current biology. According to its authors, regular exercise reduces the number of calories burned while at rest.
Error compensating mechanisms
To reach this conclusion, the researchers used data from 1,750 adults. They showed that in people with the highest BMI, 51% of calories burned during activity translated into fewer calories burned at the end of the day. On the other hand, in people with a normal BMI, 72% of calories burned during activity translate into total energy expenditure at the end of the day.
How do we explain this difference? “When they enroll in an exercise program to lose weight, most people lose quite a bit. Some people lose a lot, but a few unlucky people also see weight gain.”Professor John Speakman, co-author of the study, explains.
According to him, one of the reasons for weight gain after exercise is the so-called compensatory mechanisms: we eat more because exercise stimulates our appetite. It also happens when exercise reduces calorie expenditure when the metabolism is at rest, in order to make exercise less costly to the body.
Half of the calories are spent at rest versus one calorie spent in exercise
But what researchers have been particularly interested in is why some people have such compensatory mechanisms and others don’t. The analysis showed that two components control the extent of compensation. On the one hand, the elderly make up more. The other is obesity specifically: obese people reduce their resting metabolism when they are most active. As a result, for every calorie expended in exercise, they provide about half the calories at rest.
“This analysis shows that not all people are equal in how they budget for energy. People who are obese can be especially good at maintaining their fat stores, which can make it difficult to lose weight.”, concludes Professor Speakman.
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