More studies needed to compare weight loss with morning vs. evening physical activity
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SAN DIEGO — Weight loss can be achieved by people who exercise in either the morning or the evening, though findings on whether morning or evening physical activity is better for losing weight are mixed, according to a speaker.
During a symposium on the timing of physical activity at ObesityWeek 2022, Seth Creasy, PhD, assistant professor of medicine in the division of endocrinology, metabolism and diabetes at the University of Colorado Anschutz Medical Campus, discussed the results of a trial in which 33 adults completed four exercise sessions per week for 15 weeks, with one group exercising exclusively in the morning and the other group exercising only during the evening. At 15 weeks, both groups lost a similar amount of weight, and no differences were observed with any body composition measures.
“Exercise in the morning [and evening] is safe and feasible,” Creasy said during a presentation. “To date, we’ve really seen inconsistent weight-loss responses to morning and evening exercise, so we really can’t make recommendations on the best time of day to exercise for weight management.”
Published studies have found conflicting observations on the timing of exercise and weight loss. In a study published in 2010, adults who completed 200 minutes per week of brisk walking in the evening lost more fat mass than adults who walked in the morning. Conversely, in a study published in 2017, adults who performed aerobic exercise for 6 weeks in the morning lost more weight than adults performing the same exercise in the evening. Similarly, a 2019 study published in the International Journal of Obesity found adults who performed supervised exercise in the morning had a greater weight loss at 10 months than evening exercisers.
Similar weight loss with morning and evening exercise
Creasy said the findings from the 2019 study were from a secondary analysis and may have included adults who selected their exercise timing. Creasy and colleagues conducted a randomized trial in which 33 adults performed three supervised exercise sessions per week and one unsupervised session for 15 weeks. Participants were randomly assigned to exercise in the morning from 6 to 10 a.m. or in the evening from 3 to 7 p.m. Exercise intensity increased from 70% at the start of the intervention to 80% in the final 7 weeks. Each participant’s exercise duration was determined by their individual energy expenditure.
At 15 weeks, nearly all participants adhered to the intervention, with more than 90% of participants in both groups completing all of their sessions. Of the cohort, 94% said they enjoyed the intervention, 81% said the number of sessions per week was optimal, 55% said the exercise duration was the right amount and 91% said the intensity was optimal.
At 15 weeks, there were no differences in body weight and body composition change between morning and evening exercisers, with both groups losing about 1 kg of body weight.
Energy expenditure increased by about 200 kcal per day for morning exercisers, which was greater than the 90 kcal per day increase for the evening group. However, the amount of body weight loss was similar between the two groups because of differences with energy intake.
“The interesting part of this is the a.m. group compensated by increasing energy intake,” Creasy said. “That’s why they lost the same amount of weight [as the evening group]. They increased energy expenditure, but they also increased the food they took in, whereas the p.m. group had really no change in energy intake.”
Sleep increased in the evening exercise groups, whereas sleep decreased slightly for morning exercisers. Both groups decreased sedentary behavior, with a larger decline observed among evening exercisers.
Both the morning and evening exercise groups had changes in plasma metabolites during the intervention, and participants in both groups had unique metabolites not found in the opposite group, a finding that could hold implications for future physical activity interventions, according to Creasy.
“This is really where the work is going,” Creasy said. “Can we manipulate exercise timing to invoke the right metabolic response?”
More research needed
Creasy said there are several potential reasons studies have had conflicting findings for whether morning or evening exercise yields greater weight loss, including the small size of the studies, the population studied, the various exercise interventions and durations, a lack of objective measures and whether chronotypes have an impact.
Creasy said future studies should analyze nutrient status before and during exercise, how the timing of exercise affects the 24-hour regulation of energy balance, whether morning or evening exercise is easier to adhere to, and whether exercise can help counter circadian misalignment.
“We all know that we’re staying up later and waking up earlier because of all of these social pressures, we’re chronically sleep deprived and circadian misaligned,” Creasy said. “Can we use exercise as a countermeasure for that metabolically?”
References:
Alizadeh Z, et al. Clin Obes. 2017;doi:10.1111/cob.12187.
Di Blasio A, et al. J Sports Med Phys Fitness. 2010;50(2):196-201.
Willis EA, et al. Int J Obes. 2019;doi:10.1038/s41366-019-0409-x.
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Creasy S. Timing of physical activity: Associations with weight loss and obesity. Presented at: ObesityWeek; Nov. 1-4, 2022; San Diego.
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