(Xinhua) — A natural substance found in apple peel can partially protect mice from obesity and some of its harmful effects, according to a University of Iowa (UI) study published Wednesday in the journal PLoS ONE.

The findings suggest that the substance known as ursolic acid reduces obesity and its associated health problems by increasing the amount of muscle and brown fat, two tissues recognized for their calorie-burning properties.

Until quite recently, researchers believed that only infants had brown fat, which then disappeared during childhood. However, improved imaging techniques have shown that adults do retain a very small amount of the substance mostly in the neck and between the shoulder blades. Some studies have linked increased levels of brown fat with lower levels of obesity and healthier levels of blood sugar and blood lipid, leading to the suggestion that brown fat may be helpful in preventing obesity and diabetes.

The UI team studied mice on a high-fat diet over a period of several weeks. Half of the animals also received ursolic acid in their high-fat food. Interestingly, mice whose diet included ursolic acid actually ate more food than mice not getting the supplement, and there was no difference in activity between the two groups. Despite this, the ursolic acid-treated mice gained less weight and their blood sugar level remained near normal. Ursolic acid-treated mice also failed to develop obesity-related fatty liver disease, a common and currently untreatable condition that affects about one in five American adults.

Further study showed that ursolic acid consumption increased skeletal muscle, increasing the animals’ strength and endurance, and also boosted the amount of brown fat. Because both muscle and brown fat burn calories, the researchers investigated energy expenditure in the mice and showed that ursolic acid-fed mice burned more calories than mice that didn’t get the supplement.

“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,” said Christopher Adams, UI associate professor of internal medicine and lead author of the study.