Highly active people don’t burn more calories than those who take it easier during workouts, says a new study.

Tracking 332 adults aged 25 to 45, Hunter College researchers found energy expenditure jumps with physical activity at low levels — but “plateaus at higher activity levels,” they wrote in the journal Current Biology.

One reason may be the body adapts its metabolism, no matter how hard the workout, said researcher Herman Pontzer who said diet is the key to weight loss.