Once again we see evidence that real foods such as an apple peel can provide important health benefits to the body. Obesity and associated concerns such as diabetes and fatty liver disease are metabolic dysfunctions that are becoming more and more common. A 2012 study has shown that a natural substance found in the peel of apples can partially protect mice from obesity and some of its harmful effects.
The study, published June 20, 2012 in the journal June 20, 2012 edition of PLoS ONE, was led by Christopher Adams, M.D., Ph.D., University of Iowa associate professor of internal medicine and a Faculty Scholar at the Fraternal Order of Eagles Diabetes Research Center at the UI.
Apple Peel and Ursolic Acid
The findings suggest that a substance known as ursolic acid reduces obesity and its associated health concerns by actually increasing the amount of muscle and brown fat which are two tissues recognized for their calorie-burning properties. Ursolic acid is a lipophilic pentacyclic triterpenoid that contributes to the waxy coats on apples, other fruits, and many herbs, including some folkloric herbal medicines for diabetes.
Dr. Adams states: “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. 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.”
Researchers used to believe 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, 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.
More 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,” Dr. 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.”
The research was supported by funding from the Fraternal Order of Eagles Diabetes Research Center at the University of Iowa, the National Institute of Arthritis and Musculoskeletal and Skin Diseases of the National Institutes of Health (grant 5R01AR059115-03), the Department of Veterans Affairs, and the University of Iowa Research Foundation.
CAUTION: Apples top the Environmental Working Group’s “Dirty Dozen” List as the most pesticide-laden fruit. (See more Produce – 2016 Dirty Dozen Plus List) The EWGs states that 99 percent of apple samples tested positive for at least one pesticide residue. I highly suggest purchasing organic varieties of apples to avoid taking in potentially harmful pesticide residues.
- Kunkel SD, Elmore CJ, Bongers KS, Ebert SM, Fox DK, et al. Ursolic Acid Increases Skeletal Muscle and Brown Fat and Decreases Diet-Induced Obesity, Glucose Intolerance and Fatty Liver Disease.. PLoS ONE, 2012 DOI: 10.1371/journal.pone.0039332
University of Iowa. “Apple peel compound boosts brown fat, reduces obesity in mice.” ScienceDaily. ScienceDaily, 20 June 2012. <www.sciencedaily.com/releases/2012/06/120620212855.htm>.