Evidence reported in Current Biology helps to explain why exercise by itself isn't always enough to take off the weight: our bodies adapt to higher activity levels, so that people don't necessarily burn extra calories even if they exercise more.

The results suggest it's time to rethink the effect of physical activity on daily energy expenditure, the researchers say. They are also a reminder of the importance of diet and exercise in supporting weight loss goals.

"Exercise is really important for your health," says Herman Pontzer of City University of New York. "That's the first thing I mention to anyone asking about the implications of this work for exercise. There is tons of evidence that exercise is important for keeping our bodies and minds healthy, and this work does nothing to change that message. What our work adds is that we also need to focus on diet, particularly when it comes to managing our weight and preventing or reversing unhealthy weight gain."

People who start exercise programs 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.

Find out more about this research published in Cell Biology (28th January 2016).