Active Voice: “What a HIIT! - Implications for Exercise Guidelines for Appetite Control”

By Aaron Sim, Ph.D.

Viewpoints presented in SMB commentaries reflect opinions of the authors and do not necessarily reflect positions or policies of ACSM.

Aaron Sim, Ph.D., is an exercise physiologist and earned his Ph.D. from the School of Sport Science, Exercise and Health at the University of Western Australia in Perth. He is currently a postdoctoral research fellow at the Clinical Nutrition Research Centre, Singapore Institute of Clinical Sciences. His research interest broadly focuses on the roles of physiological and psychosocial influences on both energy expenditure and energy intake in the regulation of energy balance and prevention of metabolic disease.

This commentary presents Dr. Sim’s views on the topic related to a research article that he and his colleagues had published in the November 2015 issue of
Medicine & Science in Sports & Exercise® (MSSE).

It is becoming increasingly evident that exercise, besides directly contributing to the regulation of energy balance through energy expenditure, also may affect one’s appetite and energy intake. Importantly, it appears that the benefits of exercise for appetite regulation may be optimized by manipulating the specific type of exercise employed. This notion is supported by previous work from our group (see: Sim et al., 2014.) In that study, we found that an acute bout of high-intensity, intermittent exercise resulted in eating behavior that was beneficial for weight management in the short term (suppressed energy intake.) We also found high-intensity, intermittent exercise to be superior in suppressing energy intake compared with continuous exercise of a moderate intensity and a rest condition in an inactive and overweight population. In our follow-up study published in the November 2015 issue of MSSE, we sought to understand whether the acute appetite regulatory benefits of high intensity, intermittent exercise observed in our earlier study translated to differences in the longer term.

Our goal in the more recent study was to compare the effects of high-intensity, intermittent exercise training (HIIT) with moderate-intensity, continuous exercise training (MICT; ~60 percent VO2peak) and inactivity (control) on appetite regulation in inactive and overweight individuals. We defined HIIT as repeated 15-s bouts of higher intensity exercise, with 60-s of lighter intensity exercise interposed. We employed a preload paradigm assessment methodology for this study; this approach allowed us to assess whether participants adjusted their energy intake appropriately in response to meals of different caloric content (e.g., high vs. low energy preload meals,) before and following the exercise interventions. Given the close association previously shown between inactivity and a disruption in appetite-regulatory mechanisms, we somewhat expectedly found that, at the start of the study, participants displayed flawed eating behavior. That is, participants did not adjust their food intake appropriately in response to the different preload meals and ate a similar amount of food regardless of whether it was preceded by a high or low energy preload meal.

Following the 12-week intervention, we found that supervised HIIT performed three times weekly for 30-45 minutes on a stationary bike resulted in a clinically meaningful improvement in appetite regulation. An equivalent period and frequency of MICT or a period of remaining inactive did not have such an effect. That is, participants from the HIIT group adjusted their energy intake more appropriately ?they ate less after the high compared with the low energy preload meal. Importantly, the magnitude of this adjustment in response to HIIT (approximately 516 kJ) has been previously calculated to prevent weight gain and achieve weight loss. While the exact reasons for these findings require further study, it may be related to a decrease in insulin resistance which we observed in the HIIT group.

Another finding of equal importance was that the regular performance of HIIT did not compromise physical activity enjoyment. Furthermore, the HIIT routine was well tolerated and sustainable by the study participants. This is a consideration of significance— especially for the prescription of exercise for an overweight and inactive population with potentially low motivation and tolerance to exercise. We hope that these findings will assist health professionals and the public in making more informed decisions when determining the optimal exercise prescription for appetite control for weight loss/maintenance.