If you’re trying to help build muscle by downing eggs after a workout, a new study has some valuable advice: Don’t ditch the yolks. The post-workout muscle building-response in gym rats who consume whole eggs is actually greater than among their peers who only consumed egg whites.
After a workout, muscles build protein through what’s called, appropriately enough, protein synthesis. The point of eating eggs is to provide protein to fuel that process; throwing away the yolks was supposed to maximize protein intake, powering protein synthesis in the muscles.
But egg yolks also contain protein, as well as other nutrients and food components not found in whites. And according to Nicholas Burd, a University of Illinois professor of kinesiology and community health who led the research, they also seem to provide something that boosts the body’s protein synthesis.
"This study suggests that eating protein within its most natural food matrix tends to be more beneficial to our muscles as opposed to getting one's protein from isolated protein sources," he said in a statement.
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To reach that conclusion, researchers monitored ten young men who did one bout of resistance exercise. Afterward, they consumed 18 grams of protein, either from whole eggs or solely from egg whites. They got the same amount of protein, just from slightly different sources.
Scientists tracked a pair of important amino acids through participants’ blood and muscles. They even used specially developed eggs to track where amino acids wound up in the body after they were eaten.
They found that with either source, whole eggs or egg whites, about the same amount of dietary amino acid showed up in the blood. "In each case,” Burd said, “about 60 to 70 percent 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, as the amount of dietary amino acids in the blood after eating generally gives us an indication of how potent a food source is for the muscle-building response."
But that wasn’t the whole story. By directly measuring protein synthesis in the muscle, the saw something else. "We saw that the ingestion of whole eggs immediately after resistance exercise resulted in greater muscle-protein synthesis than the ingestion of egg whites," Burd said. And it wasn’t a small difference—those who’d eaten whole eggs had a 40 percent greater muscle-building response than those who’d only eaten egg whites.
The results suggest that consuming isolated protein isn’t as valuable as previously thought, and that there’s good reason to eat the whole egg. The finding has ramifications beyond the gym, too, as Burd points out: "As world population grows, we need cost-effective and sustainable strategies for improving the use of protein in the diet. This work is showing that consuming egg protein in its natural matrix has a much greater benefit than getting isolated protein from the same source."
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