Apple peel contains ursolic acid which can boost muscle tone and may fight against obesity, fatty- liver disease and pre-diabetes. In a just published study in the University of Iowa, researches examined the effects of ursolic acid (a waxy component in the apple peel) on the mice with high-fat diet. Their results showed that although these mice where prone to obesity, pre-diabetes and fatty liver, but ursolic acid prevented these issues and increased the muscle tone.