People do not necessarily burn extra calories even if they exercise more as their bodies adapt to higher activity levels, according to a new study.
Researchers from City University of New York measured the daily energy expenditure and activity levels of more than 300 men and women over the course of a week.
In the data they collected, they saw a weak but measurable effect of physical activity on daily energy expenditure. However, further analysis showed that this pattern only held among subjects on the lower half of the physical activity spectrum.
People with moderate activity levels had somewhat higher daily energy expenditures - about 200 calories higher - than the most sedentary people.
But people who fell above moderate activity levels saw no effect of their extra work in terms of energy expenditure.
“The most physically active people expended the same amount of calories each day as people who were only moderately active,” said Herman Pontzer of City University of New York.
There might be a ‘sweet spot’ for physical activity - too little and we are unhealthy, but too much and the body makes big adjustments in order to adapt, researchers said.
People who start exercise programmes to lose weight often see a decline in weight loss (or even a reversal) after a few months.
Large comparative studies have also shown that people with very active lifestyles have similar daily energy expenditure to people in more sedentary populations.
It is time to stop assuming that more physical activity always means more calories. The results are a reminder of the importance of diet and exercise in supporting weight loss goals, researchers said. The findings were published in the journal Current Biology.