Egg white–only eaters take notice: You are shortchanging your muscles by tossing the yolks. Research published in December 2017 in The American Journal of Clinical Nutrition shows that whole eggs build and repair muscles better than the whites alone. That’s important because we all need to maintain our muscle mass to stay active and self-sufficient as we age, and muscle burns off more calories, which helps in weight loss (or maintenance) efforts.
Background: Both the whites and yolks of eggs are packed with protein. Protein builds and repairs all your tissues. But the yolks have fat and cholesterol, too—which is why many people stick to the whites.
Study: Researchers from the University of Illinois wondered about the role of egg yolks in building and repairing muscle, so they conducted a study in which men performed resistance exercises (the kind that build muscle) and then immediately ate 18 grams of protein either from whole eggs (yolks and all) or whites alone. The researchers then observed how the eggs’ amino acids—their protein building blocks—entered the bloodstreams of the subjects and affected muscle tissue.
Findings: In all the study participants, the same amount of amino acids was available in the bloodstream to make new protein. So, at first, it looked as if getting protein from whole eggs versus whites made no difference.
But then there was an aha moment. When researchers looked at how the amino acids were used in muscle, they found a big difference. The muscle-building process was 40% greater in whole-egg eaters than in those who had eaten only whites.
This was a small study, only 10 test subjects, and further research is needed to confirm and explain why the entire egg does such a better job at building and repairing muscle. But the researchers believe something in the yolk boosts the body’s ability to use protein in muscle.
Now, you may have been told over the years that egg yolks are bad for you because they contain fat and cholesterol. But the fat in yolks is heart-healthy, and research shows that dietary cholesterol doesn’t spike blood cholesterol levels in most people. If you have high cholesterol, heart disease or diabetes, you should typically keep dietary cholesterol below 200 milligrams (mg) a day (about the amount in one large egg). If you’re healthy, that limit moves up to 300 mg. But always talk to your doctor if you’re concerned.
More good news: Yolks contain other important nutrients that aren’t in the whites. Here’s what they can do for the rest of your body…
- Protect your vision. Yolks contain lutein and zeaxanthin, two antioxidants that reduce the risk for macular degeneration and cataracts. Eggs contain vitamin A, also beneficial to your eyes.
- Keep bones healthy. You need vitamin D to move calcium into your bones. One large egg yolk has 41 international units (IU) of vitamin D. Most kids and adults under age 70 need to get at least 600 IU a day.
- Raise “good” cholesterol. It sounds counterintuitive, but the dietary cholesterol in those yolks can boost high-density lipoprotein (HDL) cholesterol, which protects against heart disease and stroke.
- Mitigate “bad” cholesterol by changing the size of low-density lipoprotein (LDL) particles from small and dense to large and fluffy. Big particles pose a lower risk for coronary heart disease than small ones.
- Boost your brain. Yolks are a good source of choline, a nutrient that helps make a neurotransmitter needed for memory, mood, muscle control and other brain functions.
Bonus: Also, there’s no reason to enjoy eggs only at breakfast or postexercise meals—they make great light dinners, too.
Brown, cage-free, organic? Learn how to choose the perfect egg here.