- Studies in mice and humans have shown that limiting food intake to the active cycle — when an individual is most active and alert — has various health benefits, including weight loss and improved blood sugar control.
- Now, a new mouse study has shown that restricting feeding to the resting period greatly improved endurance in running tests.
- This effect was surprising and unexpected, as feeding during the resting period is typically considered to be detrimental to health.
- While the findings are intriguing, further studies are needed to understand how they translate to human physiology and athletic performance.
Almost all living things, ranging from bacteria to plants to people, have physical, mental and behavioral rhythms called circadian rhythms, which follow a roughly 24-hour cycle.
Circadian rhythms are driven by
These biological clocks are coordinated by a master clock in the brain called the
Although the body has its own circadian rhythms, these rhythms may be affected by environmental stimuli. The brain’s “master clock,” the SCN, is regulated by
More recently, researchers discovered that
This led to many studies on the effects of time-restricted feeding (in animals) and time-restricted eating (in humans), where daily food intake is limited to a window of 6–12 hours.
While there is emerging evidence in humans that daytime-restricted feeding, such as observing Ramadan fasting, may improve endurance, it is still not clear how meal timing affects daily muscle rhythms and how it impacts exercise performance.
To gain a better understanding of how exercise performance is affected by eating time, a team led by Dr. Min-Dian Li, professor of internal medicine and cell biology, and director of the Center for Circadian Metabolism and Cardiovascular Disease, at Army Medical University in China, conducted a study on daytime-restricted feeding in mice.
Their findings appear in
Since mice are nocturnal creatures, daytime-restricted feeding is equivalent to feeding during the resting period — or eating at night — in humans.
Dr. Li’s team found that when mice were fed during their resting period for 3 weeks, their running time and distance doubled compared to mice that were fed freely or during their active period (night/wake time-restricted feeding). This effect was seen in both female and male mice.
Dr. Li described his team’s findings as “absolutely surprising and mindblowing”. Since daytime-restricted feeding in mice “is normally thought to be bad for metabolic health”, he had anticipated that the treadmill test “would be short”.
However, even after hours, “the mice did not show any sign of fatigue on the treadmill” and “after repeating in different cohorts with respect to sex, time of day, duration of [daytime restricted feeding], and status of exercise training, the outcome associated with daytime-restricted feeding remain[ed] robust and reproducible.” he noted.
Dr. Juleen R. Zierath, professor of physiology at Karolinska Institutet in Sweden, who was not involved in the study, observed that “the results were surprising and somewhat paradoxical. Most evidence today suggests that eating only during the [resting period] is not recommended for optimal health, but here the outcome was exercise performance.”
The researchers observed that the increased running endurance was linked to changes in the gastrocnemius muscle, the chief muscle of the calf of the leg.
Daytime-restricted feeding increased the percentage of fast-twitch oxidative type 2A muscle fibers at the expense of type 2X muscle fibers.
Interestingly, when the researchers deleted a gene called Bmal1, which is involved in regulating the circadian clock in the muscles of mice, the enhanced running capacity from daytime-restricted feeding disappeared.
The researchers also identified a specific gene called Plin5, which plays a crucial role in lipid metabolism and is regulated by Bmal1 in the muscles.
The researchers found that reducing the expression of Plin5 in mouse muscles had a similar effect to daytime-restricted feeding, promoting running performance.
Dr. Li and coworkers hypothesize that Bmal1 acts like a switch that helps to turn off the production of Plin5 in the muscles during daytime-restricted feeding.
Additionally, the researchers found that daytime-restricted feeding increased muscle and blood levels of certain substances called acylcarnitines, which help the muscles use fats more efficiently for energy.
Dr. Lawrence W. Judge, professor and coordinator of the Graduate Coaching Program at Ball State University School of Kinesiology, not involved in the study, told MNT that while the findings “appear to be significant”, “it would be premature to recommend that endurance athletes switch to a daytime-restricted feeding dietary regimen [since] [t]he findings are based on studies conducted in mice, and it is unclear how these results translate to human physiology and athletic performance.”
“Further research, including human studies, is necessary to determine the potential benefits and risks of a daytime-restricted feeding regimen for endurance athletes. Consulting with professionals in the field of exercise science, nutrition, and sports medicine would be advisable before making any specific dietary recommendations for athletes.”
– Dr. Lawrence Judge
Dr. Zierath also believes that comparable human studies are required.
“Athletes should have adequate fuels on board to perform endurance exercise”, but while “evening eating may not be a problem for athletes, [it] may be a problem for sedentary individuals and over time, may lead to metabolic dysfunction,” she cautioned.
In this study, the authors reported the greatest increase in endurance when mice ate only during their resting period.
Yet Dr. Zierath reasoned that the equivalent behavior in humans would likely interrupt sleep and “may negatively affect performance”.
When asked about the limitations of this study, Dr. Zierath mentioned the fact that the grain cereal-based diet followed by mice in this study is not representative of the kind of diet that humans typically eat.
“Additional studies would need to be performed in humans to determine how applicable meal timing and meal composition are to enhance endurance performance,” she noted.
Dr. Zierath also pointed out that, in this study, the exercise performance test was performed 2 hours after the mice went to sleep.
“Most humans do not partake in high-performance exercise 2 hours after falling asleep.” Dr. Zierath recommended that “further work should assess exercise performance at a more meaningful time.”
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