Physical activity not only helps in weight loss but also decreases the risk of various diseases such as diabetes, cardiovascular diseases, osteoporosis, stroke, and high blood pressure. While people know they should exercise, there is still a debate about the best time of day to work out for maximum benefits. A study in October 2021 discovered that exercising in the morning could be more beneficial for obese individuals, while another study in September 2021 found that evening workouts were more effective for overweight men.
A recent study published in the journal PNAS by researchers at the Karolinska Institutet in Sweden found that exercising in the morning increases fat burn compared to working out in the evening in mice models. According to Dr. Juleen R. Zierath, the lead author of the study, our internal rhythms are controlled by an intrinsic molecular clock that coordinates various body functions, including blood pressure response, hormone release, body temperature, strength, and alertness. If our daily exercise routine can align with this clock, we may be able to fine-tune the health benefits.
For this study, Dr. Zierath and her team analyzed the adipose tissue of mice after a high-intensity exercise session at two different times: late morning or late evening. The researchers found that early exercise in the morning increased the expression of genes associated with adipose tissue breakdown and higher metabolic rate. These changes happened even when the levels of exercise-induced hormones were similar between the phases. The study’s findings suggest that body fat sensitivity to exercise-induced hormones may vary depending on the time of day when the physical activity is performed.
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The scientists observed these signs of increased metabolism only in mice that exercised in the morning, which surprised them. They thought that the effect was due to nutritional status, but later confirmed that the gene signature of a higher metabolic rate was not affected by food intake. Dr. Zierath said the next step for this research is to conduct a similar study in men and women with healthy weight or obesity to understand if the findings can be applied to fine-tune exercise’s well-known benefits on metabolism.
Ryan Glatt, a senior brain health coach and director of the FitBrain Program at Pacific Neuroscience Institute in Santa Monica, California, agreed that the time of day might affect how physical activity impacts the body based on individual circadian rhythms and changes in hormones that may fluctuate throughout the day. He said there is no current scientific agreement on the “best time of day” for exercise, and it is unlikely that time of day to perform exercise outperforms the concept of “calories in versus calories out” for overall fat loss. For the next steps in this research, Glatt wants to see this type of study conducted in humans as there is a difference in mouse vs. human physiology.