The Power of ‘Chrononutrition’: How Eating Protein in the Morning Supports Muscle Growth With Age
From plants undergoing photosynthesis during the sun-drenched days to nocturnal animals hunting for food in the night’s darkest hours to humans (typically) sleeping through the night and waking in the day, almost every organism on Earth has a biological clock that ticks and tocks within a 24-hour light-dark cycle. Also known as the circadian rhythm, this internal time-telling influences dozens of bodily processes — everything from the obvious, like sleeping patterns, to the less obvious, like metabolism, immunity, body temperature, and hormone regulation.
The way we digest and absorb food is also influenced by our circadian rhythms — a recently named process known as chrononutrition. However, it’s been relatively unknown if cyclic changes in protein metabolism can then impact how our bodies assimilate it — meaning, is muscle growth affected by when we eat protein? In a recent study published in Cell Reports, researchers from Waseda University in Japan aimed to determine the muscular effects of consuming higher protein at breakfast versus dinner. Remarkably, in both mice and humans, frontloading the day with protein significantly boosted muscle mass, shedding light on how following proper chrononutrition can preserve muscle health with age.
Slowing Down Muscle Loss
Older adults are increasingly susceptible to loss of muscle mass and strength, as 80-year-olds commonly lose more than half of the muscles they had when they were young. This muscular deterioration can lead to a decline in quality of life and independence with an increased risk of frailty, falls, fractures, and premature mortality in older adults.
It’s well-known that dietary protein is important for skeletal muscle growth and maintenance. However, many older adults do not consume enough of this muscle-building macronutrient — especially at breakfast. Previous research has found that adding extra protein at breakfast and lunch increased skeletal muscle volume in adults in their 60s. Still, researchers haven’t been sure yet if the total protein distribution throughout the day is what matters most.
With this in mind, the Japan-based research team studied various combinations of protein intake and meal timing in lab mice. All mice were fed two meals per day (breakfast and dinner), which consisted of either 8.5% or 11.5% protein by proportion. From there, Aoyama and colleagues split the mice into several groups, including high protein at breakfast with low protein at dinner and vice versa.
Chrononutrition at Play
The results were striking — the mice who ate more protein at breakfast had significantly boosted muscle growth than those who consumed more at dinner. Specifically, the breakfast group had a 17% greater ratio of muscle growth in the leg’s plantaris muscle after the researchers overloaded the muscle — overloading places muscles under greater stress than usual, which helps them to adapt and grow — compared to the control leg muscle, which was not overloaded.
Notably, even when mice were fed the lower amount of protein (8.5%) at breakfast, they still had greater muscle growth than mice fed the higher amount of protein (11.5%) at dinner. With these results, it’s clear that increasing protein consumption — even moderately — in the early parts of the day is the most beneficial for muscle growth.
The ABCs of BCAAs
The research team found that a specific group of proteins called branched-chain amino acids (BCAAs) is necessary for muscle growth from early-day protein intake. BCAAs, which include leucine, isoleucine, and valine, are commonly used supplements to support muscle growth and exercise performance because they activate skeletal muscle synthesis. In this study, the mice supplemented with BCAAs at breakfast had significantly more muscle growth than those who had BCAAs at dinnertime.
As senior author, Professor Shigenobu Shibata states of the results, "[Eating a] 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."
How the Clock Gene Keeps Us Ticking
Next, Aoyama and colleagues looked at how specific genes related to the circadian rhythm were involved in these results, including the aptly-named Clock gene and a similar circadian-related gene specific to muscles, Bmal1.
In this experiment, mice had their genes modified to contain non-working versions of Clock and Bmal1 — essentially, these mice did not have a functional circadian rhythm. After subjecting the mice to the same varied protein distribution patterns, they found that consuming more protein at breakfast — whether from BCAAs or mixed protein — did not result in the same muscle-building as before, indicating that a working circadian rhythm is vital to this process.
Lastly, they looked at how eating protein at breakfast affects humans. In a sample of 60 healthy older women, the researchers split the group based on when they habitually consume more protein. They found that the women who consumed more protein at breakfast than dinner had significantly greater muscle mass, grip strength, and skeletal muscle index than those who ate more protein at dinner.
Although this wasn’t a clinical trial, the results still add to the evidence that protein consumption in the morning is better for muscular health across species. The authors conclude, “This suggests that the development of preventive interventions is important for elderly women. Our results indicate that early nutritional intervention could help address age-associated muscle loss.”
Pushing Protein at Breakfast
Professor Shibata reflects, "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."
As many people consume protein-rich foods, like meat, poultry, and fish, at the dinner meal, this study suggests that it may be time to flip that narrative and work toward pushing protein at breakfast. But this doesn’t necessarily require adding meat in the morning — try adding eggs, yogurt, steel-cut oatmeal, smoked salmon, or protein powders to your breakfast meal. (That 28 grams of protein that Shibata refers to could be met by eating two eggs and one small container of Greek yogurt — sounds [over]-easy enough!)
Aoyama S, Kim HK, Hirooka R, et al. Distribution of dietary protein intake in daily meals influences skeletal muscle hypertrophy via the muscle clock. Cell Rep. 2021;36(1):109336. doi:10.1016/j.celrep.2021.109336
Norton C, Toomey C, McCormack WG, et al. Protein Supplementation at Breakfast and Lunch for 24 Weeks beyond Habitual Intakes Increases Whole-Body Lean Tissue Mass in Healthy Older Adults. J Nutr. 2016;146(1):65-69. doi:10.3945/jn.115.219022