When it comes to losing weight, both exercise and diet are the key to success.
Hitting the gym in the hope of burning up calories to lose weight can backfire as the body adapts to higher activity levels.
The change in metabolism means that slimmers who rely on exercise to achieve their goals are likely to be disappointed, say scientists.
People who start rigorous exercise programmes to shed unwanted flab often see a decline in their rate of weight loss – or even a reversal – after a few months.
Researchers in the US investigated the phenomenon by measuring the daily energy expenditure and activity levels of more than 300 men and women over the course of a week.
They found above a certain threshold of activity, the extra work people put in had no effect on the number of calories they burned up.