Published in the American Journal of Clinical Nutrition, ten young men who partook in the study engaged in a single bout of resistance exercise and then ate either whole eggs or egg whites containing 18 grams of protein.

Researchers administered infusions of stable-isotope-labeled leucine and phenylalanine - two important amino acids - to the participants. This allowed the researchers to maintain a precise measure of amino acid levels in the participants' blood and muscles.

The researchers took repeated blood and muscle biopsy samples to assess how the egg-derived amino acids were appearing in the blood and in protein synthesis in muscles before and after the resistance exercise and eating.

The research was led by UI professor of kinesiology and community health Nicholas Burd.

He said, "By using those labeled eggs, we saw that if you ate the whole egg or the egg whites, the same amount of dietary amino acids became available in your blood.

"In each case, about 60 to 70 per cent of the amino acids were available in the blood to build new muscle protein.

"That would suggest that getting one' s protein from whole eggs or just from the whites makes no difference."

But when the researchers directly measured protein synthesis in the muscle, they found a very different response.

"We saw that the ingestion of whole eggs immediately after resistance exercise resulted in greater muscle-protein synthesis than the ingestion of egg whites," Dr Burd said.

Previous studies have suggested that this difference has nothing to do with the difference in energy content of whole eggs and egg whites.

Whole eggs containing 18 grams of protein also contain about 17 grams of fat, whereas egg whites have no fat.

The study suggests that the widespread practice of throwing away egg yolks to maximize one's dietary protein intake from eggs is counterproductive, Dr Burd said.