A substance found in apple peel increases muscles and helps burn more calories - something which could help battle the bulge, scientists say.

Researchers fed mice a high fat diet - some were also given the substance ursolic acid, others weren't.

The researchers found the mice given the acid, found in apple peel, ate more food but didn't gain weight and had near normal blood sugar levels, Medical Daily reported.

"From previous work, we knew that ursolic acid increases muscle mass and strength in healthy mice, which is important because it might suggest a potential therapy for muscle wasting," said Prof Christopher Adams, one of the authors of the study.


"In this study, we tested ursolic acid in mice on a high-fat diet - a mouse model of obesity and metabolic syndrome. Once again, ursolic acid increased skeletal muscle. Interestingly, it also reduced obesity, pre-diabetes and fatty liver disease."

Mice given the acid also had higher endurance levels, burned more calories, had more muscle and brown fat.

"Since muscle is very good at burning calories, the increased muscle in ursolic acid-treated mice may be sufficient to explain how ursolic acid reduces obesity," Prod Adams said.

"However, we were surprised to find that ursolic acid also increased brown fat, a fantastic calorie burner. This increase in brown fat may also help protect against obesity."

Previous studies have shown that apple peels are a rich source of antioxidants and polyphenols.

The study is published in PLoS ONE.