Researchers at Harvard Medical School say they may have discovered a way to help people lose kilos without even breaking a sweat.

They believe the hormone irisin is released when animals and people exercise, and it tells the body to burn fat faster.

The hormone turns on a gene that converts white fat into brown fat, which burns more calories for longer.

However, the development of a drug for human consumption could take up to a decade, and scientists say their findings so far only scratch the surface of irisin's multiple effects.

Al Jazeera's Charlie Angela reports.