Proteins are essential for body growth and muscle development. However, protein metabolism varies depending on the body’s internal biological clock. Therefore, it is important to know how distributing protein intake throughout the day affects muscles. Researchers have found that eating protein for breakfast increases muscle size and function in mice and humans, shedding light on the concept of “chrononutrition,” which looks at the timing of food intake to ensure organ health.

Chrononutrition and the Right Time of Day to Eat Protein

Proteins are an important part of the diet that help the body grow and repair itself. They are made up of long chains of amino acids and help the growth of skeletal muscle, the group of muscles that help us move. The benefits of proteins have been known to humans for a long time. However, recent studies have shown that eating the right amount of proteins at the right time of the day is essential for healthy growth. This is known as chrononutrition, where when you eat is just as important as what and how you eat. This is because of the body’s internal biological clock, known as the circadian rhythm. This rhythm is followed by all cells and governs vital functions such as metabolism and growth. Interestingly, protein digestion and absorption have been found to fluctuate according to this clock throughout the day and night. In addition, previous studies have shown that protein intake at breakfast and lunch promotes skeletal muscle growth in adults. However, the exact effects of the time of protein intake on muscle growth and muscle function have remained unclear. Researchers at Waseda University, led by Professor Shigenobu Shibata, wanted to understand the effects of the distribution of protein intake throughout the day on muscles.

They fed two meals per day to laboratory mice, with either a high (11.5% by proportion) or low (8.5% by proportion) protein content. The researchers found that consuming protein at breakfast time led to an increase in muscle growth compared to the effects of consuming protein at dinner time, as determined by evaluating induced hypertrophy of the plantaris muscle in the leg. Specifically, the ratio of muscle hypertrophy compared to the growth of the control muscle in mice that received 8.5% protein for breakfast was 17% higher than in mice that consumed 11.5% protein for dinner, even though the former group ate a low percentage of protein overall. Researchers also found that taking in a type of protein called BCCA, short for branched-chain amino acids, early in the day increased skeletal muscle size.

Changing Our Eating Habits: The Key to Healthy Muscles

To confirm the link of these effects with the functioning of the circadian rhythm, the researchers next developed whole-body mutants of the clock^?19 or muscle-specific Bmal1 knockout mice, which lack the genes that control the biological clock. They repeated the experiments on food distribution in these mice, but were unable to observe similar muscle changes, which confirmed the involvement of the circadian rhythm in muscle growth in connection with protein intake. According to Prof. Shibata, a high-protein diet in the early phase of daily activity, i.e. at breakfast time, is important to maintain healthy skeletal muscles and improve muscle volume and grip strength. To see if their findings could be applied to humans, the team recruited women for their study and tested whether their muscle function, determined by measuring skeletal muscle index (SMI) and grip strength, varied with when the high-protein food was consumed.

Sixty women aged 65 and over who ate protein for breakfast instead of dinner showed better muscle function, suggesting that the results may apply to all genders. In addition, the researchers found a strong link between SMI and the proportion of protein intake at breakfast relative to total protein intake throughout the day. Prof. Shibata is confident that the results of her study will lead to widespread changes in the current eating habits of most people in Western and Asian countries, who traditionally consume only small amounts of protein at breakfast. The results clearly support eating more protein at breakfast or as a morning snack. A simple change in our eating habits could be the key to healthy muscles.