The Controversy Surrounding Exercise's Impact on Weight Loss: Examining Evidence from Both Perspectives

The global fitness industry is projected to surpass US$80 billion in revenue in 2023, reflecting the widespread recognition of the myriad health advantages associated with regular exercise. These benefits encompass enhanced cardiovascular health, reduced risk of Type 2 diabetes, and a fortified immune system, among others.

A primary motivation for many individuals to engage in exercise is weight loss. As a bio-behavioral scientist, I investigate the connections between behavior and health, acknowledging the conventional wisdom advocating for a combination of reduced calorie intake and increased physical activity to achieve weight loss. However, a recent discourse within the scientific community has cast doubt on the efficacy of the "exercising more" aspect of this advice.

At the crux of the debate lies the constrained total energy expenditure hypothesis, which posits that exercise may not substantially increase overall calorie expenditure, as the body compensates by reducing post-exercise calorie burning. Consequently, this theory suggests that while exercise offers numerous health benefits, it may not significantly contribute to weight loss.

Critics of this hypothesis, particularly obesity researchers, question its validity due to its reliance on observational data rather than randomized controlled trials (RCTs), which are considered the gold standard in scientific research. RCTs involve randomly assigning participants to treatment or control groups, enabling researchers to establish causal relationships between interventions and outcomes. Notably, RCTs have consistently demonstrated the effectiveness of exercise in promoting weight loss.

However, the interpretation of evidence from RCTs regarding the relationship between exercise and weight loss remains contentious, with divergent conclusions drawn from the available gold-standard research. Despite this ongoing debate, it is widely acknowledged that exercise provides a multitude of health benefits beyond weight management.

Advocates of the constrained total energy expenditure hypothesis have highlighted the significance of systematically evaluating evidence from all gold-standard trials. They cited a comprehensive 2021 review encompassing over 100 studies on exercise, which investigated the impact of various exercise modalities, including aerobic, resistance, or high-intensity interval training, either in combination or alone, on weight loss in adults. The findings of this review indicated that supervised exercise regimens do lead to weight loss, albeit to a modest degree.

However, does this settle the debate entirely? Can one simply compensate for overindulging in dessert by engaging in extra physical activity?

Not quite.

If additional physical exertion does indeed result in increased overall calorie expenditure, then logically, exercise should also help prevent weight regain after a period of low-calorie dieting. However, maintaining weight loss achieved through dieting poses a common challenge. The same 2021 review included a subset of randomized controlled trials investigating whether exercise aids in weight maintenance. Surprisingly, the results were not as promising as those for weight loss. Researchers discovered that engaging in six to twelve months of aerobic exercise, resistance training, or a combination of both following a period of dieting did not effectively prevent weight regain in adults.

Compliance with exercise regimens and the intricacies of energy balance shed light on the complexities of weight management.

Regarding adherence, the 2021 review identified only one randomized controlled trial focusing on weight maintenance that reported an objective compliance rate, indicating supervised exercise sessions. Despite this supervision, the compliance rate among participants, particularly post-menopausal women completing a resistance training program, stood at 64%. While this rate may seem reasonable given the duration and intensity of the regimen, participants still experienced weight regain comparable to those who did not engage in the exercise program.

The concept of energy balance, which emphasizes the equilibrium between caloric intake and expenditure, is often touted as pivotal in weight management. However, the American College of Sports Medicine highlighted the uncertainty surrounding the optimal exercise dose for weight maintenance in its 2009 position statement. Furthermore, the lack of randomized controlled trials employing advanced techniques to monitor participants' energy balance complicates the understanding of this aspect.

Intriguingly, a 2015 study investigating energy expenditure revealed unexpected findings. Despite exercisers burning additional calories during sessions, their total daily calorie expenditure did not significantly differ from non-exercisers. This discrepancy underscores the constrained total energy expenditure hypothesis, which posits that regular exercise prompts the body to adjust metabolism, potentially offsetting the additional calories burned during physical activity.

Recent research further explored this hypothesis by examining the nonexercise calorie burn of obese adults before and after a six-month exercise program. Results indicated a decrease in calorie burn during periods of inactivity, particularly among those prescribed higher exercise doses. This phenomenon suggests that the body adapts to regular exercise by moderating non-exercise calorie expenditure, potentially hindering weight management efforts.

While exercise may offer modest contributions to weight loss, the diminishing marginal return emphasizes the importance of dietary interventions in conjunction with physical activity. Despite its limited efficacy in weight management, regular exercise remains indispensable for overall health, offering a multitude of benefits beyond weight control.