|I know, this may be disappointing, but the study at hand won't settle the debate once and for all.|
In their latest study, scientists from the Sports Medicine Research Center and the Department of Sports and Exercise Medicine at the Teheran University of Medical Science did now try to get to the bottom of the "early is better"-myth.
Based on the observation that exercise can significantly affect your appetite, wich almost 16% of the interventional trials that evaluated the correlation between physical activity and food intake showing that volunteers’ appetite decreases after exercise, and the majority indicating that it remained unchanged, they speculated that the often-cited mechanism, i.e. an increase in fatty acid oxidation with AM training (done in the fasted state) could be irrelevant compared to the effects of early exercise on (obese) subjects' appetite and thus food intake within a given 24h period.
As Alizadeh, et al. point out in the corresponding paper in Clinical Obesity (Alizadeh 2017), "there are few studies that consider the effect of a single session of exercise at different times of day on appetite or food consumption". In view of the "lack of time, as is a common barrier in modern life," the authors do yet believe that "exercise should be undertaken at the best time of day in order to obtain maximal appetite suppression and greater weight loss" (ibid.). To figure out, whether this time is in the morning or the evening they conducted a 6-week study to compare the effect of 6 weeks of morning or evening aerobic exercise on appetite and anthropometric indices in N=48 20–45-year-old female participants with body mass index (BMI) of between 25 and 29.9 kg/m². Inactive patients were chosen "to eliminate the effects of other types of exercise on outcomes" (ibid.) and "to decrease the risk of musculoskeletal injuries during exercise testing and prescribed aerobic exercise" (ibid.).
A total of 25 patients participated in the morning aerobic exercise (ME) as group 1 and scheduled to perform their supervised training sessions within 8–10 AM, while the other subjects had to report at the lab between 2–4 PM. All exercise session included 30 min treadmill running in the VT heart rate (this is when you can no longer talk to someone without breathing heavily).
|Figure 1: Baseline demographics, anthropometric measurements and physical characteristics of the study participants; data are expressed as mean ± SD unless otherwise stated. (Alizadeh 2017).|
|Figure 1: Changes in anthropometric variables over the course of the 6-week study (Alizadeh 2017).|
Table 2: Summary of 24-h food records over time in the morning and evening exercise groups (Alizadeh 2017).
- the effects on the subjects' energy intakes differed significantly [the subjects in the AM group consumed -17% less energy; most of the reduction came from carbs | Table 2]
- an increased reduction in abdominal skinfold thickness in the AM (add. 3.8%), and
- an increased reduction in suprailiac skinfold thickness in the PM (add. 5.6%) group,
- Alizadeh, Z., Younespour, S., Rajabian Tabesh, M. and Haghravan, S. (2017), Comparison between the effect of 6 weeks of morning or evening aerobic exercise on appetite and anthropometric indices: a randomized controlled trial. Clinical Obesity. doi: 10.1111/cob.12187