The supplements could be useful for trauma victims (severe trauma diminishes the body's ability to make new muscle) and hospitalised elderly people, say the University of Texas researchers.
Writing in this month's issue of the Journal of Clinical Endocrinology & Metabolism (vol 89, no 9, pp 4351-4358), they report giving 13 healthy male volunteers, all confined to bed for 28 days, either a drink containing essential amino acids and carbohydrates or a placebo three times a day.
Using data produced by state-of-the-art real-time muscle-protein synthesis measurements, biopsies, magnetic resonance and X-ray imaging, and strength tests, the researchers found the supplemented group retained all of their original leg muscle mass while the members of the placebo group lost about a pound of leg muscle on average.
Those given the supplements also lost only about half as much leg strength as those given the placebo.
"We thought it was the most astounding thing that even though our subjects did no exercise, they were able to maintain muscle mass," said the university's medical branch assistant professor Douglas Paddon-Jones, lead author on the paper.
A similar supplement regime could reduce muscle loss in elderly people.
"The elderly have less muscle to spare than the rest of us," Paddon-Jones said. "When they get sick or injured and wind up in a hospital bed for a prolonged period, many of them lose so much muscle mass and strength that they don't get back up. For a lot of people, this supplement could make a real difference."
The subjects in this study were aged between 26 and 46. The researchers plan further investigations to determine whether nutritional supplements - alone and in combination with resistance or walking exercise- can indeed significantly reduce muscle loss in elderly men and women during prolonged bed rest.
In a BBC report on the study however, Michael Rennie, an expert in muscle wasting in the elderly from Nottingham university, pointed out that one pound loss of leg muscle in the control group was actually very small.
He also told the news service that his research had shown the elderly to have a limited ability to utilise amino acids so relying on nutritional supplements for this group was unlikely to work. Resistance exercises could be a more effective way of minimising muscle wastage.
Studies have also found fish oil supplements may help to prevent the wasting and weight loss associated with some types of advanced cancer while creatine, used by bodybuilders to increase muscle mass, could also have similar clinical applications.