In the heat of summer, the crisp, cool fall apple season might feel far away. But it will be here before you know it, and there is good reason to celebrate this year: apple skins contain ursolic acid. What’s that? Ursolic acid is a compound found in the skins of apples, as well as cranberries, basil and some other fruits and vegetables, which may boost metabolism. New research published in the June 2012 issue of PLoS One finds that mice fed a high-fat diet with ursolic acid had faster metabolisms when compared to mice fed only the high-fat diet.
What was especially interesting was the mechanism in which metabolism was increased. It was not due simply to an increase in muscle mass in the mice, which happened as well, but also to an increase in brown adipose tissue, or brown fat. Brown fat is the type of fat involved in warming up the body and thus, unlike its white counterpart, it burns calories rather than storing them.
The researchers were especially excited by the increase in brown fat. Brown fat is most active in newborns and helps them keep warm without shivering. In past years, researchers have tried to uncover ways to increase brown fat in older adults but without much luck. Brown fat did increase when people were exposed to cold temperatures for long periods of time; presumably activated to help warm up the body. However, it’s a lot easier to eat apples than stand outside in the cold.
The researchers were unsure how and why the brown fat was increased in the mice. In past studies, brown fat has been increased in humans by placing them in extremely cold conditions for a long time. Because brown fat burns calories, it has been a hot topic in recent years. However, the long-term effects of boosting brown fat in humans remain unclear. Would an increase in metabolism also increase appetite? Would the brown fat stay active for a long time? Would there be other negative side effects? The answers to these questions are not yet known.
In the study, the mice getting ursolic acid also exhibited lower rates of obesity, better blood glucose levels, and less fatty liver disease. In addition, the mice had increased slow and fast twitch muscles and ran faster on a treadmill than their counterparts. The research implies that ursolic acid essentially helped the mice gain less weight and get stronger and faster, all while minimizing the risk of certain diseases. Sounds pretty great. However, the research is still very preliminary.
While the latest study done on ursolic acid in mice seems promising, so far no studies have been done to test the effects of ursolic acid in humans. It’s a good idea to eat apples with the skin on, especially because apples are high in fiber and other vitamins and minerals, but there is no guarantee that they will keep the doctor away or boost your metabolism.
*sources available upon request
Lisa D’Agrosa is a second year nutrition communication student at Tufts. She loves apples, especially with peanut butter or some nice sharp cheddar. When she’s not chomping on her fruits and veggies, you can find her on a yoga mat or walking around the beautiful city of Boston.