Summary: New research indicates that exercising during the late morning may boost metabolism and enhance fat burning more than exercising late in the evening. These findings could be useful for people aiming to lose weight or improve metabolic health by scheduling their workouts at specific times of day.
Source: Karolinska Institute
Exercise timing appears to shape how the body uses fat, at least in a mouse model.
A collaborative study from Karolinska Institutet (Sweden) and the University of Copenhagen (Denmark) examined how the time of day when exercise is performed affects adipose tissue metabolism. Using mice as a model, the researchers compared the effects of high-intensity exercise performed during the animals’ early active phase (analogous to late morning exercise for humans) with exercise performed during their early rest phase (analogous to late evening exercise for humans).
The study, published in PNAS, shows that exercise during the early active phase triggers stronger metabolic responses in adipose tissue. The research team measured markers of fat breakdown, mitochondrial activity and gene expression in white adipose tissue immediately after exercise to determine how time of day influenced these processes.
The team analyzed multiple indicators of fat metabolism and performed gene-expression profiling in adipose tissue. Their findings point to a clear time-of-day dependence: when exercise was undertaken during the animals’ early active phase, the adipose tissue showed stronger activation of pathways linked to lipolysis (fat breakdown), thermogenesis (heat production) and mitochondrial proliferation—signals consistent with a higher metabolic rate.
Independent of food intake
Importantly, these metabolic differences were observed independently of immediate food intake. Exercise during the early active phase elevated the expression of genes involved in adipose tissue breakdown and energy production even when controlling for feeding, indicating that the timing of activity itself altered tissue responses.
“Our results suggest that late morning exercise could be more effective than late evening exercise in terms of boosting metabolism and enhancing fat burning,” says Professor Juleen R. Zierath from the Department of Molecular Medicine and Surgery and the Department of Physiology and Pharmacology at Karolinska Institutet. “If this pattern translates to humans, timing could become an actionable factor for people aiming to reduce adiposity.”
Improve the health benefits of exercise
Mice are widely used to model human physiology and metabolism, and many basic mechanisms are shared across species. That said, there are important differences to consider—most notably, mice are nocturnal while humans are typically diurnal. These differences mean that direct translation of timing effects from mice to people requires careful validation.
The study highlights how the circadian clock—a cell-autonomous timing system that regulates gene expression across tissues—can interact with behaviors such as exercise to shape metabolic outcomes. The research suggests that aligning physical activity with certain phases of the circadian cycle may improve the metabolic benefits of exercise. However, Professor Zierath cautions that further studies in humans are needed to confirm whether the same timing effects occur in people and how best to apply them in clinical or lifestyle recommendations.
About this exercise and metabolism research news
Author: Press Office
Source: Karolinska Institute
Contact: Press Office – Karolinska Institute
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Original Research: Open access. Title: “Time of day determines postexercise metabolism in mouse adipose tissue” by Pendergrast, Logan A. et al., published in PNAS.
Abstract
Time of day determines postexercise metabolism in mouse adipose tissue
The circadian clock is a cell-autonomous transcription–translation feedback mechanism that anticipates and adapts physiology and behavior to different phases of the day. Factors such as hormones, temperature, feeding, and exercise act on tissue-specific peripheral clocks and can change gene expression in a time-of-day dependent way, thereby influencing metabolism.
To investigate how exercise timing affects adipose tissue metabolism, the authors conducted RNA sequencing on inguinal adipose tissue from mice immediately after maximal exercise or a sham treatment delivered at either the early rest phase or the early active phase. Only exercise in the early active phase produced an immediate increase in circulating nonesterified fatty acids and elevated the expression of genes associated with thermogenesis and mitochondrial proliferation in inguinal adipose tissue.
In vitro experiments with synchronized 3T3-L1 adipocytes revealed timing-dependent differences in Adrb2 expression and increased lipolytic activity at specific time points, supporting a role for intrinsic circadian regulation in the adipose response to exercise. To assess whether feeding state could explain the timing effects, a separate experiment replicated early rest phase exercise after a 10-hour fast to mimic the metabolic state of the active phase. While the fast produced a similar lipolytic response, it did not reproduce the same transcriptomic changes, suggesting that the gene-expression response is not solely driven by feeding status.
In conclusion, acute exercise provokes timing-specific effects in adipose tissue that contribute to maintaining metabolic homeostasis, and these effects may be partly driven by the circadian clock. Further research, especially in human subjects, is needed to determine how exercise timing can be optimized to enhance metabolic health.