Active Voice: Might Habitual Physical Activity Help Control Appetite?

By Kristine Beaulieu, M.S., R.D.

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

Kristine Beaulieu, M.S., R.D., is a dietitian and Ph.D. student in the Appetite Control and Energy Balance research group at the University of Leeds, UK. She investigates the impact of habitual physical activity on the mechanisms of appetite control. Prior to her doctoral studies, she completed an M.S. degree in kinesiology, in which she examined the effects of sprint interval exercise on appetite at the University of Western Ontario, Canada. Ms. Beaulieu has been a member of ACSM since 2013.

This commentary presents Ms. Beaulieu’s views on the topic of a research article that she and her colleagues authored together. Their article appeared in the November 2017 issue of
Medicine & Science in Sports & Exercise® (MSSE).

Understanding the role of physical activity in appetite control is important, as it is an integral (and readily modifiable) component of energy balance and body weight. Dr. Jean Mayer and colleagues demonstrated in 1956 that the relationship between physical activity level and energy intake is J-shaped rather than linear. Therefore, it was proposed that low levels of physical activity may lead to a dysregulation of appetite and subsequent overconsumption in inactive individuals. In 2016, we completed a systematic review that confirmed this J-shaped relationship (Beaulieu et al., Sports Med, 2016). Our view is that physical activity impacts appetite control through a dual-process action. Further, this influence seems to be expressed through an increased drive to eat due to greater energy requirements, together with an enhanced satiety response to food. These two processes allow more accurate “matching” of energy intake to energy expenditure, because of stronger hunger and satiety signals ? perhaps thereby helping reduce the risk of overconsumption.

It has been well established that physical activity improves body composition in both men and women. More specifically, negative associations between objectively measured physical activity and adiposity have been observed in individuals across a range of body mass index scores. In addition, evidence has amassed showing that significant reductions in body fat will occur in inactive overweight and obese individuals following exercise training interventions lasting a few months or longer. However, it is also important to note that large interindividual variability exists in the body fat response to exercise training. For a more extensive treatment of the issues, see the 2009 ACSM Position Stand on Appropriate Physical Activity Intervention Strategies for Weight Loss and Prevention of Weight Regain for Adults.

In a study that I conducted with my research colleagues, as published in the November 2017 issue of MSSE, we set out to examine homeostatic and hedonic (liking or wanting for high-fat foods) appetite responses to high- and low-energy porridge preloads in individuals who varied in their level of habitual physical activity. We classified 34 non-obese individuals according to sex-specific tertiles of daily minutes of measured moderate-to-vigorous physical activity obtained from a validated multisensor device worn for five-to-seven days. Following a preliminary assessment where several determinants of appetite control were measured (e.g., body composition, resting metabolic rate, eating behavior traits), participants underwent three laboratory probe days in a crossover design that included a fixed breakfast (25 percent of resting metabolic rate), a high-energy (~700 kcal), low-energy (~260 kcal) or control (0 kcal) preload three hours later, followed by an ad libitum lunch (one hour after the preload), dinner and evening snack box to examine 24-hour energy intake. The design was based on our understanding that appetite is controlled by several homeostatic processes that signal hunger (drive to eat), satiation (termination of eating) and satiety (post-meal suppression of hunger), which, in turn, determine food intake. These homeostatic mechanisms interact with non-homeostatic processes, such as food reward (hedonics), in the overall expression of appetite. Evidence suggests that habitual physical activity improves post-meal satiety; however, previous research on this issue had not objectively assessed physical activity levels or 24-hour energy intake. Furthermore, prior to this study, the effect of physical activity level on the hedonic response to food preloads was unknown.

The results provide confirmatory evidence for enhanced appetite control in individuals classified with moderate-to-high levels of habitual physical activity who showed better compensation following consumption of the preloads such that they reduced energy intake to offset the difference in energy consumed from the preloads. In contrast, the individuals with habitually low levels of physical activity were insensitive to our nutritional manipulation, indicating a weaker satiety response to food. The hedonic response to the preloads did not differ in these individuals, suggesting that the compensatory appetite response to the preloads appeared to be mediated by homeostatic rather than hedonic mechanisms. The physiological mechanisms behind the improved satiety remain to be fully elucidated but are likely related to postprandial peptide signaling.

Therefore, the findings from our study indicate that inadequate physical activity levels may contribute to obesity not only through low energy expenditure, but also by weakened homeostatic appetite control that can lead to overeating.