Do you throw your egg yolks away every morning when you cook breakfast? If you do, and you've noticed your muscles aren't as strong as they used to be, then you might want to stop. That's because new research suggests eating eggs without the yolks is hurting your ability to build muscle.
In fact, a new study suggests there's a dramatic difference in the way your muscles respond to yolks compared to just the egg whites. This difference is so dramatic, you may never throw the yolk away again.
According to the study, the post-workout muscle-building response in those eating whole eggs is a whopping 40% greater than in those who eat the same amount of protein from egg whites.
The reason will seem obvious when you read it. You've probably heard that colorful vegetables have more nutrients than white vegetables. Well, the same is true of the egg. The yolks don't just contain protein. They also have key nutrients and other food components that are not present in the white of the egg. And one of those components (though we don't know which one) is boosting your muscles' ability to use that protein.
Here's how the researchers discovered this. They had 10 young men workout using resistance exercise (weightlifting). Then they had them eat either whole eggs or egg whites containing 18 grams of protein. Notice the amount of protein they ate was exactly the same. The researchers then gave the participants two amino acids - leucine and phenylalanine. The amino acids allowed the researchers to maintain and precisely measure the amino acid levels in their blood and muscles.
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To do this study, the researchers used eggs that they had isotopically labeled with leucine. This allowed them to precisely track where the food-derived amino acids ended up after participants ate them. If they found the labeled leucine in the blood, they knew it came from the eggs they ate.
So here's what they found. About 60-70% of the labeled leucine was available in the blood from all of the participants. That means it didn't matter whether they ate the whole egg or just the white, the same amount of leucine made it into the blood. So both the yolk and the white are equally good sources of protein. No surprise there.
The big surprise came when the researchers measured protein synthesis in the muscles. There was a huge difference. The whole egg group experienced a much greater surge in mTOR. This is an important cell-signaling complex for muscle growth. The higher the levels of mTOR, the greater the synthesis of protein. The study's lead author, Nicholas Burd (a University of Illinois professor of kinesiology and community health) said, "We saw that the ingestion of whole eggs immediately after resistance exercise resulted in greater muscle-protein synthesis than the ingestion of egg whites."
Some people have suggested the fat content in the yolks is what causes the increased protein synthesis. Yolks have about 17 grams of fat compared to zero grams in the white (this is the reason many people avoid the yolk). But studies have shown that the fat doesn't increase protein synthesis.
So what's in the yolk that helps build muscle? That's easy: vitamins, minerals, phytonutrients, phenols, etc. All those same nutrients a young chick would need to grow are exactly what your muscles need to grow. A chick won't grow if you feed it just the egg white (it needs the yolk - its primary food source). Why do we think our muscles would do any better?
And let's not forget the role amino acids play in protein synthesis. You've got to have enough amino acids available for your body to build muscle. Even the researchers in this study knew the value of amino acids. So make sure you're taking an amino acid supplement, such as Perfect Amino, along with your whole eggs.
Your insider for better health,
Steve Kroening, ND.