Barbara Fiorillo
It is known that regular physical activity is good for body and mind, at any age. While on the one hand it improves mood and makes you more energetic and toned, on the other it reduces blood pressure, keeps blood sugar and cholesterol levels low, helps prevent metabolic and neoplastic diseases and reduces the risk of certain types of cancer. For these reasons, the World Health Organization recommends that people between the ages of 18 and 64 get 150-300 minutes of moderate-intensity physical activity each week, or 75-150 minutes of vigorous-intensity exercise each week (or an equivalent combination of the same).
However, the results of exercise vary depending on the time of day in which you train, because they directly depend on circadian rhythms, which regulate sleep-wake cycles. The best time to exercise remains a controversial topic, with some researchers suggesting morning exercise improves muscle adaptations and fuel utilization, while others believe afternoon/evening exercise is more conducive to improving function. muscle. Now a new search driven by the Karolinska Institutet in Sweden and fromUniversity of Copenhagen in Denmark has shown, in a mouse model (on mice), that training in the late morning, compared to an evening workout, causes an increase in metabolism and fat burning. “If we can also demonstrate these results in a clinical study (on humans), this discovery could prove very useful for all overweight or obese people,” the researchers said. The results were published in the journal PNAS.
Circadian rhythm and metabolism
Almost all cells in the body have an internal biological circadian clock synchronized by external stimuli. This mechanism anticipates and adapts the body’s physiology during the 24-hour day-night cycle. A variety of factors including hormones, temperature, food intake and exercise can affect this clock by altering the expression of genes that affect metabolism, all in a time of day dependent manner. In this study, the researchers tested the hypothesis that the timing of energy stressors affecting glucose and energy homeostasis (equilibrium state), namely exercise and nutrition, may affect differentially the metabolic response in adipose tissue.
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I study
To ascertain how the time of day in which exercise is performed affects fat burning, the researchers performed the RNA analysis of the adipose tissue of mice (divided into two groups) after an exercise session at high intensity performed in two moments of the day, a first active phase and a first resting phase (corresponding respectively to a late morning and late evening session in men). The researchers studied various markers to examine both fat metabolism and the expression of the genes involved.
Working out late in the morning burns more fat
Even though the type of exercise was the same, the researchers found a big difference in the metabolism of the mice in the two groups. Physical activity in the early active phase (i.e. late in the morning) resulted in higher expression of genes involved in the breakdown of fat tissue, higher levels of heat production in the body (thermogenesis), and more mitochondria in fat tissue, all indicators of a faster metabolism. These results demonstrate that adipose tissue response to exercise is sensitive to the time of day at which it takes place, and may be in part driven by the circadian clock.
“Our results suggest that late morning exercise may be more effective than late evening exercise in terms of speeding up metabolism and burning fat,” said Prof. Juleen. R. Zierath, who led the study.
The effect is independent of food intake
The study also demonstrated that this effect is independent of dietary status. To determine how this affects adipose tissue response to late morning exercise, the researchers replicated the experiment by subjecting 10-hour fasted mice to a session of high-intensity exercise performed in the early (late evening) rest phase. for humans), to mimic the metabolic state of the early active phase (late morning). The adipose tissue response was the same: 10-hour fasting resulted in a lipolytic response similar to that seen after late-morning exercise.
However, the transcriptomic response (gene expression) was not the same: this suggests that intense exercise elicits a specific effect (linked to the time of day in which it takes place) on adipose tissue, but that this is independent of diet (fasting or full stomach).
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A human study is needed
Mice and humans share many basic physiological functions. and mice are an established model for investigating human physiology and metabolism. However, there are also important differences between the two, such as the fact that mice are nocturnal. “The right timing appears to be important for energy balance in the body and for enhancing the health benefits of exercise,” Zierath concluded. “But more studies are needed to draw reliable conclusions about the relevance of our findings to humans.” .