Apple peel every day may keep the fat away
Apple peel contains a muscle-pumping ingredient that could form the basis of new treatments to keep people in shape.
The waxy substance, ursolic acid, has been shown to promote muscle growth and reduce wasting in mice. It also reduced levels of fat, blood sugar, and cholesterol in the animals.
Scientists believe the compound could be used to treat muscle wasting and possibly metabolic disorders such as diabetes.
But whether enough is consumed as part of a normal human diet to be beneficial is not yet known.
Study leader Dr Christopher Adams, from the University of Iowa in the US, said: "Muscle wasting is a frequent companion of illness and ageing.
"It prolongs hospitalisation, delays recoveries and in some cases prevents people from going back home. It isn't well understood and there is no medicine for it."
The researchers first looked at what happened to gene activity in muscles when they are made weaker. They found 62 genes that altered their activity in response to food restriction in both humans and mice. A further 29 human genes responded both to fasting and to spinal cord injuries.
Information from the genetic studies was used to screen more than 1,000 molecules in search of any that might counteract muscle atrophy. This led the scientists to ursolic acid, which is found in many plants but is especially concentrated in apple peel.
Tests showed that it caused a pattern of gene activity the opposite of the one involved in muscle wasting.
Follow-up experiments confirmed that mice fed ursolic acid were protected from muscle atrophy induced by both fasting and nerve damage.
Healthy mice given the compound developed larger and stronger muscles than other animals.
They also became leaner, and had lower blood levels of glucose, cholesterol and harmful fats called triglycerides.
Dr Adams, who now hopes to study ursolic acid in human trials, believes the compound may be responsible for some of the benefits of healthy eating.
"We know if you eat a balanced diet like mam told us to eat you get this material," he said. "People who eat junk food don't get this."