An apple a day .......

[Marco]

.... may increase muscle strength and mass, improve exercise tolerance and prevent metabolic syndrome and fatty liver disease.

If the mouse model findings hold true for humans :

Apple Peel Compound Boosts Brown Fat, Reduces Obesity in Mice

"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.

http://www.sciencedaily.com/releases/2012/06/120620212855.htm

and more science :

Ursolic Acid Increases Skeletal Muscle and Brown Fat and Decreases Diet-Induced Obesity, Glucose Intolerance and Fatty Liver Disease

In summary, we found that ursolic acid increases skeletal muscle, brown fat and energy expenditure in a mouse model of diet-induced obesity. These effects are associated with increased strength and exercise capacity, and reduced obesity, improved glucose tolerance and decreased hepatic steatosis.

http://www.plosone.org/article/info:doi/10.1371/journal.pone.0039332