Laboratory studies have found that the skin on an apple contains a substance that not only promotes muscle growth and prevents the loss of muscle that comes with aging, but may also lower blood sugar, cholesterol, and triglycerides.
In addition to vitamins, minerals, fiber, and other substances such as antioxidants and phytochemicals that are known to protect against cancer and other forms of chronic disease, apples contain a chemical called ursolic acid. Scientists at the University of Iowa found that ursolic acid helps build muscle tissue and prevent muscle wasting in laboratory mice, and also cleared their blood of excess fat, cholesterol and sugar.
Human research studies have also found that eating an apple a day reduces blood levels of LDL cholesterol (the bad kind) and increase levels of HDL cholesterol (the good kind) in postmenopausal women. And back to animal research, substances found in apple flesh and peel have been shown to interfere with the growth of breast tumors and the development of Alzheimer's disease in rats and to extend the lifespan of fruit flies by ten percent, while at the same time, preserving their ability to walk and climb.
For a lab animal, then, an unpeeled apple is a proverbial fountain of youth, but what does it mean to you? Until the results of human trials are in, no one knows for sure. What researchers do know, however, is that genetic testing of people with muscle atrophy showed that ursolic acid may help block the progression of tissue wasting. This knowledge led the University of Iowa scientists to test the effects of ursolic acid in mice.
There are already so many reasons to eat an apple a day, it's hardly worth waiting for confirmation of a new one. The older you get, the fewer calories you need, so if you are eating less to try to maintain a healthy weight, it becomes more and more important for the foods you do eat to be rich in nutrients. Fruits like apples definitely fall into that category. In addition to an array of essential nutrients, unpeeled apples provide both soluble fiber, the kind that helps keep your arteries clear and prevent atherosclerosis and heart disease, and insoluble fiber, the kind that helps keeps your digestive tract healthy and prevent constipation.
There are many easy ways to incorporate unpeeled apples into your diet besides just eating them out of hand. Try adding freshly diced apples to salads, yogurt, mixed fruit compotes, and your morning cereal. Cook unpeeled diced or sliced apples with sweet potatoes, winter squash, chicken or pork dishes.
Sources:
American Chemical Society: Polishing the Apple's Popular Image as a Healthy Food Web 7 Dec 2011
Kunkel, S, et al; "mRNA Expression Signatures of Human Skeletal Muscle Atrophy Identify a Natural Compound That Increases Muscle Mass." Cell Metabolism 2011; 13(6): 627-638 Web 7 Dec 2011. http://www.cell.com/cell-metabolism/retrieve/pii/S155041311100177X
Peng, C, et al. "Apple Polyphenols Extend the mean Lifespan of Drosophila Web 7 Dec 2011 Melanogaster." Journal of Agricultural and Food Chemistry 2011; 59 (5): 2097-2106 Web 7 Dec 2011 http://pubs.acs.org/doi/abs/10.1021/jf1046267
University of Iowa: Apple Peel Makes Mice Mighty Web 7 Dec 2011 http://news-releases.uiowa.edu/2011/june/060711ursolic_acid.html
