Morning vs. Evening Workouts for Weight Loss: When is the Best Time to Exercise? (Evidence-Based Insights)

Welcome to Active Life Health! Today, we're diving into a common question: when is the optimal time to exercise for weight loss? A recent randomized controlled trial by Brooker et al. (2023) sheds light on this intriguing topic, providing valuable evidence-based insights for overweight and obese adults.

1. Research Objective & Background: Debunking the "Best Time" Myth

Obesity is a growing global concern, and exercise is a cornerstone of weight management. Clinically significant weight loss (> 5%) often requires a substantial amount of exercise (> 250 minutes/week). However, despite this emphasis, clear, consistent evidence on how the timing of exercise affects weight loss has been lacking. This gap often leaves the public wondering: "When is the best time to exercise for weight loss?"

The need for this study was clear: "This highlights the need for well-designed, large-scale randomized controlled trials to understand how exercise timing influences weight loss". Previous research often suffered from small sample sizes, a lack of specific design to detect differences between exercise timings, no explicit weight loss goals, and insufficient objective measures. Many also allowed participants to self-select their exercise times, potentially skewing results.

2. Study Design & Methodology: A Robust Approach

This study was a 12-week, three-arm randomized controlled trial involving 100 inactive overweight or obese adults (BMI ≥ 25 kg/m²). Participants were randomized into one of three groups: Morning Exercise (AMEx), Evening Exercise (PMEx), or a Wait-List Control (CON) group.

Participants:

• Individuals had stable weight for 3 months prior to the study.
• Excluded participants included those who were pregnant, shift workers, involved in weight loss programs, or taking weight-affecting medications.

Exercise Prescription:

• AMEx Group: Performed self-guided aerobic exercise (treadmill-based) for 250 minutes/week between 6:00 AM and 9:00 AM.
• PMEx Group: Performed self-guided aerobic exercise (treadmill-based) for 250 minutes/week between 4:00 PM and 7:00 PM.
• CON Group: Maintained their usual activity.
• The 250 minutes/week aligns with the American College of Sports Medicine's recommendation for clinically significant weight loss.

Measurement Variables:

• Body Composition: Weight, fat mass, lean mass, and body fat percentage were tracked at baseline, 6, and 12 weeks, with follow-ups at 3 and 6 months.
• Cardiometabolic Health: Maximal oxygen uptake (V̇O2peak), blood pressure, lipid profiles, and blood glucose were measured at baseline and 12 weeks, with V̇O2peak also at 3 and 6 months.
• Energy Balance Components: Resting metabolic rate (RMR), physical activity (via accelerometers), and dietary intake (24-hour recalls) were assessed at baseline, 6, and 12 weeks.

Key Features:

• A blend of supervised and unsupervised sessions encouraged exercise habit formation.
• Exercise intensity was monitored via heart rate and Rating of Perceived Exertion (RPE).
• Individual chronotype (morning/evening preference) was also evaluated.
• Information provision and behavioral approaches were included to facilitate behavior change.

3. Key Results & Findings: Consistency Trumps Timing

The study found that both morning and evening exercise were effective for weight loss and improving cardiometabolic health, with **no statistically significant differences** observed between the two time slots.

Weight Loss:

• AMEx group lost an average of 2.7 kg, and the PMEx group lost an average of 3.1 kg. Both groups showed statistically significant weight loss (p < 0.001).
• A higher, though not statistically significant, proportion of PMEx participants achieved clinically significant weight loss (> 5% of initial body weight) compared to AMEx (PMEx 33% vs. AMEx 19%).
• Exercise groups continued to show weight loss even after the intervention, with PMEx maintaining a significant reduction at 6-month follow-up.

Cardiometabolic Health:

• V̇O2peak significantly increased in both exercise groups and differed from the control group (AMEx +4.7 mL/kg/min, p = 0.034; PMEx +4.2 mL/kg/min, p = 0.045).
• A higher, though not statistically significant, proportion of PMEx participants achieved clinically meaningful V̇O2peak improvements (≥3.5 mL/kg/min) compared to AMEx (PMEx 75% vs. AMEx 69%).
• Systolic blood pressure significantly decreased in PMEx, and diastolic blood pressure significantly decreased in both exercise groups.
• Fasting blood glucose decreased in PMEx, and total cholesterol decreased in AMEx, both significantly differing from the control group.
• "There were no statistically significant differences between AMEx and PMEx for any cardiometabolic health risk factor".

Energy Balance:

• Total energy intake significantly decreased in both exercise groups compared to the control (AMEx -3974 kJ, p < 0.001; PMEx -3165 kJ, p = 0.001).
• No significant differences were found in RMR or non-exercise physical activity between groups or over time.

Exercise Compliance & Enjoyment:

• No significant differences were found between the two exercise groups in terms of exercise compliance, program adherence, self-selected exercise intensity, or exercise enjoyment.

4. Conclusion & Future Research Directions: Just Move!

This study provides strong evidence that for overweight and obese adults, engaging in exercise, whether in the morning or evening, is effective for weight loss and improving cardiometabolic health. Crucially, it found **no compelling evidence that a specific exercise timing is superior to another for weight loss**.

Key Message:

"We did not find compelling evidence to support or encourage exercise at a specific time of day for weight loss".

Practical Implication:

This supports the widely accepted notion that exercise needs to be integrated into an individual's daily routine. The findings align with Mayo Clinic's Dr. Michael Joyner's message: "'Do something' is far more important than 'do something at a specific time'".

Recommendations for Future Research:

• Consistent reporting of exercise timing in future intervention studies is needed to provide more insights into the relative importance (or lack thereof) of prescribing exercise at specific times.
• Further investigation into the non-statistically significant trend of higher rates of clinically significant weight loss and V̇O2peak improvement in the PMEx group is warranted.
• Improvements in dietary measurement methods are needed in future studies, as inaccuracies in self-reported dietary intake (under-reporting) may explain discrepancies between observed and expected weight loss.

This briefing document summarizes the key information and implications from the research by Brooker et al. (2023). It helps to clarify common misconceptions about the importance of exercise timing, reinforcing the vital message that **consistent exercise, regardless of the time of day, is what truly matters.**

Reference: Brooker, P. G., Gomersall, S. R., King, N. A., & Leveritt, M. D. (2023). "The efficacy of morning versus evening exercise for weight loss: A randomized controlled trial." Obesity, 31(1), 83-95.

Disclaimer: This information is derived from a scientific research study. Always consult with a healthcare professional for personalized medical advice and treatment plans.