It says 45 minutes of moderate-intensity aerobic exercise burns far more body fat than the short, sharp bursts of exertion touted by some experts.

Although high-intensity interval training improves fitness, it is not effective for weight loss, say the researchers from the Charles Perkins Institute at the University of Sydney.

They compared the two types of training on groups of overweight and unfit people.

"To slim your core and positively improve your body fat composition, the ideal is to spend 45 minutes, three times a week, doing traditional endurance exercise," exercise researcher Shelley Keating says.

Add three to five minutes for a warm-up and another few minutes to cool down, says Ms Keating, who is lead author of a paper on the study published in the Journal of Obesity.

"Some trainers spruik high-intensity workouts as the most efficient training method but this doesn't mean it translates to fat loss if you're overweight," co-researcher Dr Nathan Johnson says.

But this is based on studies using people who were already lean and healthy, he says.

The researchers compared the two types of aerobic training but Ms Keating says it is healthy to include resistance training, such as weights or circuits, in a weekly exercise regime.

"For fat loss, do resistance training alongside aerobics training, not instead of it," she says. AAP