Updated: Jul 23
In this article, we discuss a recent randomised controlled trial published in the journal “Obesity” that compared the effect of morning vs. evening exercise for weight loss.
We all know that exercise is good for us. However, the influence of when we exercise is something that has only recently been considered as perhaps important. Just last month, a large analysis of nearly 100,000 individuals from the UK showed that while moderate-to-vigorous physical activity was associated with a lower risk of death over the roughly 7-year follow-up period (no duh), exercising in the evening was not associated with a significant reduction in risk, whereas exercising in the morning was (1). With respect to weight loss, the effect of morning vs. evening exercise has not been tackled in a large, robust clinical study… until now.
One hundred adults with overweight or obesity were recruited to take part in a 12-week randomised controlled trial (2). Participants were separated into three groups:
Forty were randomly put into the morning exercise group
Forty were randomly put into the evening exercise group
Twenty were randomly put into the wait-list control (comparison) group
Participants in the exercise groups were instructed to perform 250 minutes of self-paced treadmill-based exercise per week, for a total of 12 weeks. The effect of morning compared to evening exercise on body weight, body fat %, fat mass, and fat-free (lean) mass was then assessed.
After 12 weeks, both exercise groups lost significant amounts of weight, fat mass, lean mass, and reduced their body fat % compared to the beginning of the intervention. However, when comparing average reductions in these outcomes, there were no significant differences between groups (e.g., both groups lost an average of ~3 kg of body weight). There was, however, a difference between groups in the amount of people who lost clinically meaningful amounts of weight (> 5% of their original body weight): 33% of those in the evening group achieved this feat compared to 19% in the morning group.
Those in each exercise group also ate less total energy (kJ) throughout the study compared to when they began, which may further explain the weight loss. In addition, participants in both groups significantly improved their cardiorespiratory fitness (VO2max). Eight people in the morning exercise group dropped out of the study before completion, which was comparable to the evening exercise group (seven dropouts), meaning that both times of day were roughly equally acceptable.
This study found no compelling evidence to suggest that exercising in the morning compared to the evening is better for weight loss. More studies will be needed to confirm these results, but it would seem that actually doing the exercise is the biggest factor for weight loss. Until further notice, I would suggest that you exercise when it suits you if you are looking to shift a few pounds.
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That’s all for this week! Next week we will touch upon the topic of mental health in football, so tune in then :)
Patrick Elliott, BSc, MPH
Health and Nutrition Science Communication Officer at Training121
Founder of Just Health — Instagram: @just.health.info
Health Disclaimer: this article is for informational and educational purposes only, and is not a substitute for professional advice. For health advice, speak to a physician or other qualified health-care professional, and for nutrition advice, speak to a qualified nutrition professional (e.g., registered dietitian). The use of information on this site is solely at your own risk.
(1) Feng H, Yang L, Liang YY, et al. Associations of timing of physical activity with all-cause and cause-specific mortality in a prospective cohort study. Nat Commun. 2023;14(1):930. Available at: https://www.nature.com/articles/s41467-023-36546-5
(2) Brooker PG, Gomersall SR, King NA, Leveritt MD. The efficacy of morning versus evening exercise for weight loss: A randomized controlled trial. Obesity (Silver Spring). 2023;31(1):83-95. Available at: https://onlinelibrary.wiley.com/doi/10.1002/oby.23605
Statistical significance: This is a term to describe the likelihood of whether a finding in a study is a “real” finding, or if it is the result of chance. Statistical significance is denoted by a p-value, which is usually set at a significance (alpha) level of 0.05. This means that if a result is significant at this level (p < 0.05), we can say that the probability of getting a value as or more extreme than the observed value (under the assumption that the null hypothesis is true) is less than 5%.
Randomised controlled trials: Also known as RCTs, these are a type of intervention study where a group of recruited individuals are randomly assigned to groups within a study. The rationale for randomisation is to reduce bias, that is, to evenly distribute among groups any factors that may influence (or bias) the result of interest. For example, if we have a group of 100 people who will either be given a multivitamin or placebo and followed for 10 years to see how many in each group dies, we would randomise so that each group is on average similar for factors like age, physical activity status, smoking status, and so on. If we didn't randomise, there's a greater chance that one group may end up being different enough from another group such that the results of the study may be biased, e.g., one group could have a lot more smokers or sedentary individuals, which would likely influence the outcome of interest (death).
VO2max: This is the maximum rate of oxygen consumption attainable during physical exertion, and is measured as mL of oxygen consumed per kg of body weight per minute (mL O2/kg/min). Athletes (particularly endurance athletes) have a greater VO2max compared to untrained individuals.