Protein sources – meat, fish, cheese, nuts, beans and greens.

Protein sources in food (© nadianb -

TOKYO, Japan — Breakfast is already called the most important meal of the day, but a new study is giving people even more reason to chow down in the morning. Researchers in Japan have discovered that when people take in certain nutrients is just as important as what they eat. Specifically, consuming rich sources of protein earlier in the day helps to build stronger muscles than eating them at night.

Proteins are an essential part of a healthy diet. Foods like meat, poultry, nuts, beans, and even certain fruits and vegetables all contain what the body needs to build muscles and promote growth. However, the study finds our bodies metabolize protein differently depending on our internal biological clock — the circadian rhythm.

Researchers studying the concept of “chrononutrition” — or the importance of when you consume nutrients — found that mice eating protein in the morning displayed increased muscle size and function than mice having protein at night. The team confirmed their results in a group of women over the age of 65 as well.

Why is protein so good for growing muscle?

Proteins consist of long-chain amino acids which promote the growth of skeletal muscles. These particular muscles help the body move.

As for the timing of taking in nutritious proteins, researchers say the circadian rhythm is what all cells in the body follow. It controls various life processes, such as a person’s metabolism, sleep cycle, and development. With that in mind, previous studies have discovered that the absorption of proteins seems to decrease later in the day, when the circadian rhythm feels it’s time for the body to sleep.

To find out how much of a difference this makes, Professor Shigenobu Shibata from Waseda University and a team of scientists examined a group of mice eating a high-protein diet. These animals consumed one of two meals per day, one with an 8.5-percent protein concentration at breakfast or one with an 11.5-percent concentration at dinner.

Results show, even though the mice consumed less protein, they displayed more muscle growth in their legs after the morning meal than at night. In comparison to a control group, muscle enlargement after breakfast was 17 percent greater than the growth displayed by mice eating protein at dinner.

The team adds that consuming branched-chain amino acids (BCCA) earlier in the day appears to increase skeletal muscle size too.

Timing is everything

To confirm their findings, study authors completed two additional experiments. The first involved genetically-altered mice that did not have a working biological clock. Researchers repeated the diet experiment and discovered that the mice with no circadian rhythm did not see the same increase in muscle size at breakfast.

“Protein-rich diet at an early phase of the daily active period, that is at breakfast, is important to maintain skeletal muscle health and enhance muscle volume and grip strength,” Prof. Shibata emphasizes in a university release.

In the second test, researchers recruited 60 older women to consume a protein-rich diet at different points in the day. The group ate their proteins at either breakfast or dinner, with study authors measuring their muscle function using the skeletal muscle index (SMI) and grip strength tests. Again, the results reveal that protein in the morning leads to better muscle function among humans as well as mice.

“For humans, in general, the protein intake at breakfast averages about 15 grams, which is less than what we consume at dinner, which is roughly 28 grams. Our findings strongly support changing this norm and consuming more protein at breakfast or morning snacking time,” Prof. Shibata concludes.

The study author hopes the findings prompt a change in the way both Western and Asian cultures approach breakfast. Both societies, he adds, traditionally consume lower amounts of protein during their morning meals.

The study appears in the journal Cell Reports.

About Chris Melore

Chris Melore has been a writer, researcher, editor, and producer in the New York-area since 2006. He won a local Emmy award for his work in sports television in 2011.

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