A recent Iowa University (UI) study shows you might be doing your body a disservice by peeling your apples and tomatoes, as their skins may help combat muscle loss and weakness caused by aging.

Very little is known about the causes of age-related muscle weakness and atrophy, according to the U.S. university, which is why researchers launched a study to discover the effect these natural products may have on muscle mass.

The research team, led by professor of internal medicine at UI Carver College of Medicine, Christopher Adams, discovered the first example of a protein that causes muscle weakness and loss during aging.

The protein, ATF4, is a transcription factor that alters gene expression in skeletal muscle, causing a reduction in muscle protein synthesis, strength and mass.

The UI study also identifies two natural compounds, one found in apples and the other in green tomatoes, which reduce ATF4 activity in aged skeletal muscle.

The findings, were published in the Journal of Biological Chemistry earlier this month, could lead to new therapies.

"Many of us know from our own experiences that muscle weakness and atrophy are big problems as we become older," says Adams.

"These problems have a major impact on our quality of life and health."

During previous studies, professor Adam and his team identified ursolic acid, found in apple peel and tomatidine found in green tomatoes, as small molecules that can prevent acute muscle wasting caused by starvation and inactivity.

This set the stage for the latest study using elderly mice with age-related muscle weakness to determined whether ursolic acid and tomatidine may block atrophy.

They were fed diets lacking or containing either 0.27% ursolic acid, or 0.05% tomatidine over a two month period. Scientists found both compounds increased muscle mass by 10% and muscle quality or strength by 30%.

Scientists say these effects suggest the compound largely restored muscle mass and strength to young adult levels.

"Based on these results, ursolic acid and tomatidine appear to have a lot of potential as tools for dealing with muscle weakness and atrophy during aging.

"We also thought we might be able to use ursolic acid and tomatine as tools to find a root cause of muscle weakness and atrophy."

The study also found both compounds turn off a group of genes that are turned on by the transcription factor ATF4. A new strain of mice that lack ATF4 in skeletal muscle were engineered and a study discovered old muscles lacking ATF4 were resistant to the effects of aging.

"By reducing ATF4 activity, ursolic acid and tomatidine allow skeletal muscle to recover from effects of aging."

The UI study was carried out in collaboration with Emmyon Inc, a UI-based biotechnology company founded by Adams, working to translate ursolic acid and tomatidine into foods, supplements and pharmaceuticals that can help recover strength and muscle mass as people grow older.

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