As the age-old saying goes, you are what you eat. Now, new scientific findings are expanding that idea. When it comes to muscle growth, it’s also about when you eat.

It all revolves around the body’s internal biological clock, known as circadian rhythm. Many body functions, including protein digestion and absorption, fluctuate with the time of day. Scientists have known generally that eating protein at breakfast and lunch encourages muscle growth in adults. Now, they know much more about how protein consumption throughout the day affects muscles.

To establish their findings, researchers at a university in Japan fed laboratory mice two meals a day. One group of animals got a high-protein diet with an overall protein content of about 12%. The other group received lower-protein meals. In terms of muscle growth, the researchers determined that timing was everything. The mice that ate lower-protein meals in the morning gained more muscle mass than the ones who ate higher-protein evening meals.

To confirm that time-of-day protein consumption was related to circadian rhythm, they also tested the diets on mice that lack the genes that control the biological clock. Those animals experienced no similar muscle growth.

But would this also hold true in humans? Indeed, it did. The scientists tested a group of 60 older women for muscle function and grip strength. Those who consumed protein for breakfast instead of dinner had better muscle function.

Since most people typically eat twice as much protein at dinner as they do at breakfast, it’s time to consider flipping the morning meal routine: Put down the cereal spoon and grab some eggs.