Effects of chronic exercise intervention on gastric emptying

Many studies have linked altered gastric emptying (the rate at which food empties from the stomach into the small intestine) to increased food intake and obesity. Although findings comparing lean and obese individuals are inconsistent, previous research in non-obese adults indicates an inverse association between gastric emptying rate and body mass index. Physical activity has been implicated as a modifiable lifestyle factor which may alter the delivery of nutrients to the small intestine. However this is based on limited cross sectional research comparing physically active and sedentary individuals. Surprisingly, no longitudinal studies could be found. In addition, gastric emptying has received little investigation as a potential mechanism which may explain changes in appetite and food intake with exercise. The aim of this thesis therefore is to determine changes in gastric emptying, appetite sensations and food intake with chronic exercise interventions. Two longitudinal experimental studies are presented, the first involving a 7- week exercise intervention in a cohort of 19 adolescent schoolgirls, and the second a 10- week intervention study in a cohort of 12 Multiple Sclerosis patients. Gastric emptying was assessed using the 13C-octanoic acid breath test. Increasing BMI was demonstrated to be signficantly associated with slower gastric emptying for the first time in a population of female adolescents. A 7 week exercise intervention had no effect on gastric emptying or food intake at an ad libitum buffet meal but hunger sensations at 30 minutes after the test meal assessed by visual analogue scales were significantly reduced following intervention when compared to a control group. Using heart rate variability analysis as an additional indicator of autonomic nervous system function in Multiple Sclerosis patients, no significant difference in changes in gastric emptying or heart rate variability were found following exercise intervention when compared to a control group. Three day food diary records indicated a significant increase in food intake following exercise intervention but significantly reduced hunger sensations were observed over 4 hours after the test meal following exercise intervention compared to changes in the control group. The combined findings of this thesis suggest that chronic exercise intervention does not significantly alter gastric emptying in these populations but suppresses postprandial hunger sensations when compared to a control group. The accelerated gastric emptying previously observed by others in more active individuals may therefore be due to other lifestyle factors such as diet. Alternatively exercise interventions of increased weekly energy expenditure or duration may be needed to significantly alter gastric emptying. These studies provide the foundation to future work in this area.