Background: Understanding of the impact of an acute bout of exercise on hormones involved in appetite regulation may provide insight into some of the mechanisms that regulate energy balance. In resting conditions, acylated ghrelin is known to stimulate food intake, while hormones such as peptide YY (PYY), pancreatic polypeptide (PP) and glucagon-like peptide 1 (GLP-1) are known to suppress food intake.
Objective: The objective of this review was to determine the magnitude of exercise effects on levels of gastrointestinal hormones related to appetite, using systematic review and meta-analysis. Additionally, factors such as the exercise intensity, duration and mode, in addition to participant characteristics, were examined to determine their influence on these hormones.
Data sources: Major databases (PubMed, Scopus, Google Scholar, Science Direct, Academic Search Premier and EBSCOHost) were searched, through February 2013, for original studies, abstracts, theses and dissertations that examined responses of appetite hormones to acute exercise.
Study selection: Studies were included if they evaluated appetite hormone responses during and in the hours after an acute bout of exercise and reported area under the concentration-time curve (AUC) values for more than three datapoints. Studies reporting mean or pre/post-values only were excluded.
Study appraisal and synthesis: Initially, 75 studies were identified. After evaluation of study quality and validity, using the Physiotherapy Evidence Database scale, data from 20 studies (28 trials) involving 241 participants (77.6 % men) had their data extracted for inclusion in the meta-analyses. A random-effects meta-analysis was conducted for acylated ghrelin (n = 18 studies, 25 trials) and PYY (n = 8 studies, 14 trials), with sub-group analyses and meta-regressions being conducted for moderator variables. Because the number of studies was limited, fixed-effects meta-analyses were performed on PP data (n = 4 studies, 5 trials) and GLP-1 data (n = 5 studies, 8 trials).
Results: The results of the meta-analyses indicated that exercise had small to moderate effects on appetite hormone levels, suppressing acylated ghrelin (effect size [ES] Cohen's d value -0.20, 95 % confidence interval [CI] -0.373 to -0.027; median decrease 16.5 %) and increasing PYY (ES 0.24, 95 % CI 0.007 to 0.475; median increase 8.9 %), GLP-1 (ES 0.275, 95 % CI -0.031 to 0.581; median increase 13 %), and PP (ES 0.50, 95 % CI 0.11 to 0.89; median increase 15 %). No significant heterogeneity was detected in any meta-analysis (using Cochrane's Q and I (2)); however, publication biases were detected for all analyses. No moderator variables were observed to moderate the variability among the studies assessing acylated ghrelin and PYY.
Limitations: The majority of the present literature is acute in nature; therefore, longer-term alterations in appetite hormone concentrations and their influence on food and beverage intake are unknown. Furthermore, our review was limited to English-language studies and studies reporting AUC data.
Conclusions: An acute bout of exercise may influence appetite by suppressing levels of acylated ghrelin while simultaneously increasing levels of PYY, GLP-1 and PP, which may contribute to alterations in food and drink intake after acute exercise. Further longitudinal studies and exploration into mechanisms of action are required in order to determine the precise role these hormones play in long-term appetite responses to an exercise intervention.