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Dieters, Think Before You Peel That Apple

Apple peels may help dieters

Dieters know how hard it is to drop those extra pounds, so anything that helps make that task even a little easier is usually welcome. The results of a new study fall into that category, and it involves apple peels.

Apples may keep more than doctors away

It's hard not to like apples; after all, they're crunchy, portable, tasty, nutritious, readily available, and inexpensive. Much of the nutritional value of apples are in the peel, yet we are often told to remove the peel before eating the fruit, unless it's organic.

Now scientists at the University of Iowa (UI) may give you a reason to keep that peel on. Under direction of Christopher Adams, associate professor of internal medicine, they found that apple peels contain a compound called ursolic acid, and that it helped reduce obesity, pre-diabetes, and fatty liver disease in mice.

In previous research by the same investigators, they found that the waxy substance in apple peels called ursolic acid reduced muscle atrophy, promoted muscle growth and loss of fat, and lowered levels of blood sugar cholesterol, and triglycerides in mice.

In that earlier study, Adams called ursolic acid an "interesting compound" and noted that the apple peel compound worked by "helping two hormones that build muscle: insulin-like growth factor-1 (IGF1) and insulin."

In the current study, the results of which appear online in PLoS One on June 20, Adams and his team evaluated the use of ursolic acid in mice fed a high-fat diet to model obesity and metabolic syndrome and compared them with mice fed the same diet without the apple peel compound. While ursolic acid increased skeletal muscle as expected, it also increased brown fat, which is very good at burning calories, while it also reduced obesity, pre-diabetes, and fatty liver disease.

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Another surprise was that the mice that ingested ursolic acid ate more food but gained less weight, burned more calories, and also had near-normal blood sugar levels than the mice that didn't get the apple peel compound.

More on ursolic acid
Ursolic acid, also known as urson, prunol, and micromerol, is found in a wide range of plants and herbs, including apple peels, cranberries, sage, and peppermint. Analysis of ursolic acid has revealed that it has anti-inflammatory, antitumor (skin cancer), and antimicrobial properties.

Folk medicine used plants that contain ursolic acid long before it was known what was responsible for their therapeutic abilities. Treatment with ursolic acid can improve the health of hair and skin, and it's been used to treat sun-damaged skin to prevent wrinkles and age spots.

Use of ursolic acid may also inhibit the growth of some common bacteria and significantly reduce inflammation. In Japan, ursolic acid also has been suggested as a topical treatment for skin cancer.

Overall, the authors concluded that their findings "support a model in which ursolic acid reduces obesity, glucose intolerance and fatty liver disease by increasing skeletal muscle and brown fat, and suggest ursolic acid as a potential therapeutic approach for obesity and obesity-related illness."

Will keeping the peels on your apples help you in your fight against obesity? That remains to be determined by future studies, but given the nutritional value of apples and apple peels and the possibility of help with weight loss, it seems like a good idea.

Kunkel SD et al. Ursolic acid increases skeletal muscle and brown fat and decreases diet-induced obesity, glucose intolerance and fatty liver disease. PLoS One 7 (6): e39332
Kunkel SD et al. mRNA expression signatures of human skeletal muscle atrophy identify a natural compound that increases muscle mass. Cell Metabolism 2011 Jun 8;13(6):627-38

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