The apple is one of the most widely cultivated tree fruits. Apples grow on small, deciduous trees. The tree originated in Western Asia, where its wild ancestor is still found today. Apples have been grown for thousands of years in Asia and Europe, and were brought to North America by European colonists. Apples have been present in the mythology and religions of many cultures, including Norse, Greek and Christian traditions. When one thinks of an apple one thinks more of the delicious fruit inside and not the skin outside. A new study by University of Iowa researchers shows that a natural substance found in apple peel can partially protect mice from obesity and some of its harmful effects. 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.
The study, which was published June 20 in the journal PLoS ONE, was led by Christopher Adams, UI associate professor of internal medicine and a Faculty Scholar at the Fraternal Order of Eagles Diabetes Research Center at the UI.
“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," Adams says. "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.
"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."
Brown adipose tissue or brown fat is one of two types of fat or adipose tissue (the other being white adipose tissue or white fat) found in mammals.
It is especially abundant in newborns and in hibernating mammals. Its primary function is to generate body heat in animals or newborns so as not to shiver.
Until quite recently, researchers believed that only infants had brown fat, which then disappeared during childhood. However, improved imaging techniques have shown that adults retain a very small amount of the substance mostly in the neck and between the shoulder blades.
The UI team, which also included Steven Kunkel, Christopher Elmore, Kale Bongers, Scott Ebert, Daniel Fox, Michael Dyle, and Steven Bullard, 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.
"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," Adams says. "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."
For further information see Apple Skin.
Apple image via Wikipedia.