Weight loss: How intense exercise may backfire, leading to weight gain

The researchers also evaluated how circadian rhythm, the body’s natural sleep and wake cycle, played a role in activity by examining the stress hormone corticosterone, which regulates the circadian rhythm.

While exercise has numerous health benefits, its impact on weight loss can sometimes be less than anticipated.

This could be due to a decrease in physical activity following exercise, though the exact mechanism remains unclear.

Corticosterone, which follows a circadian rhythm — is lowest at bedtime and peaks around the time we wake up —regulates both physical and mental activity levels.

In this study, researchers hypothesized that even a single session of high-intensity exercise could disrupt this rhythm, leading to decreased physical activity, lower heat production and diminished weight loss effects.

To test this hypothesis, mice were divided into three groups: high-intensity exercise, moderate-intensity exercise and rest. Their physical activity and core body temperature, indicators of heat production, were monitored before and after exercise.

The researchers also noted a disruption in the synchrony between physical activity and body temperature. They confirmed a positive correlation where relatively low blood corticosterone levels during wake times were associated with reduced physical activity.

These findings indicate that a single session of high-intensity exercise can disrupt corticosterone’s circadian rhythm, leading to decreased physical activity, lower body temperature and weight gain.

This study underscores the importance of considering not just the calories burned during exercise but also the subsequent activity levels and circadian rhythm when designing exercise regimens for effective weight loss.

Lead researcher Takashi Matsui, PhD, from the Institute of Health and Sport Sciences at the University of Tsukuba in Japan, explained the key findings to Medical News Today:

“Our study found that while exercise is a powerful strategy for weight loss, a single session of high-intensity exercise that induces heavy sweating can significantly reduce subsequent physical activity and core body temperature, leading to weight gain. Interestingly, this weight gain occurs despite no changes in food intake.”

Matsui added that “these phenomena are likely due to disruptions in the circadian rhythm of the stress hormone corticosterone and disturbances in the synchronization between physical activity and body temperature.”

“Therefore, it is important to consider not only the energy expenditure during exercise but also the subsequent activity levels and circadian rhythm when setting appropriate exercise intensity for effective weight loss,” Matsui said.

Ryan Glatt, CP, senior brain health coach and director of the FitBrain Program at Pacific Neuroscience Institute in Santa Monica, CA, not involved in the research, pointed out that “this animal study questions the benefits of vigorous exercise for weight loss, suggesting it might actually cause weight gain by reducing activity levels afterward and disrupting body temperature.”

“The research, conducted on mice, shows that high-intensity workouts may have complex effects on metabolism that aren’t fully understood,” Glatt said.

Mark A. Anton, MD, medical director at Slimz Weightloss, also not involved in this research, described the study as fascinating.

“It’s important to recognize that while vigorous exercise has its benefits, it can also lead to reduced activity levels outside of exercise sessions and potentially impact body temperature regulation. This can sometimes counteract weight loss efforts if not managed properly,” Anton explained.

Matsui highlighted that the research “adds new evidence to the emerging theory that animals, including humans, tend to compensate for the energy expenditure of exercise (especially a single bout of high-intensity exercise) by reducing energy use in other activities.”

“Therefore, it is crucial to recognize the beneficial effects of maintaining an active lifestyle beyond just exercise,” Matsui noted.

Glatt agreed, saying that, “overall, this study suggests rethinking the focus on intense exercise, considering the potential benefits of more moderate and consistent activity for weight loss.”

However, “It’s important to note that these results are from animal studies and may not directly apply to humans,” Glatt highlighted.

“For weight loss and weight management, I recommend a balanced approach that includes a mix of moderate-intensity aerobic exercises, such as brisk walking or cycling, combined with resistance training. This combination helps to burn calories, build muscle, and maintain a higher metabolic rate. It’s also crucial to incorporate rest and recovery to prevent burnout and ensure sustainable progress.”

— Mark A. Anton, MD

“To fully benefit from exercise, it is important to engage in moderate exercise that does not hinder overall daily activity and to perform this exercise regularly rather than sporadically,” Matsui said.

“This approach would ensure that the benefits of exercise are sustained and do not inadvertently lead to weight gain,” he concluded.