A substance found in apple peel increases muscles and helps burn more calories - something that might help against obesity and related complications - says a new study.

The substance called ursolic acid has now been shown to have effects on mice that were kept on a high fat diet.

For the study, all mice were fed on high fat diet. One set of mice received ursolic acid along with the diet while the other set did not.

The researchers found that mice that were on high fat plus ursolic acid ate more food than other mice. Despite this, mice that got ursolic acid in the diet did not gain weight and had near-normal blood sugar levels. These mice did not develop fatty liver disease as well.

"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. 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," said Dr. Christopher Adams, UI associate professor of internal medicine and one of the authors of the study.

Mice that were given ursolic acid also had higher endurance levels than normal mice. They burned more calories than the rest and had more muscles and brown fat in their bodies.

Ursolic acid increases muscle mass and brown fat, helping fight off obesity and most of the risk factors associated with it.

"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. 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," Adams added.

Previous studies have shown that apple peels are a rich source of antioxidants and polyphenols. Eating an apple a day also reduces risk of lung and colon cancer.

Another study suggested that powdered apple peel can be added to food products to increase phytochemical levels.

"Our study suggests that ursolic acid increases skeletal muscle and brown fat leading to increased calorie burning, which in turn protects against diet-induced obesity, pre-diabetes and fatty liver disease. Brown fat is beneficial and people are trying to figure out ways to increase it. At this point, we don't know how ursolic acid increases brown fat, or if it increases brown fat in healthy mice. And, most importantly, we don't know if ursolic acid will benefit people. Our next step is to determine if ursolic acid can help patients," Adam said.

The study is published in PLoS ONE.