Anticipation of aerobic exercise increases planned energy intake for a post-exercise meal

Abstract

In many situations, meals are planned (i.e. what and how much) before they are eaten, but how exercise influences this planning is unknown. Therefore, this study investigated whether anticipation of an exercise session alters food intake planned for post-exercise. Forty (16 male) regular exercisers (mean ± SD; age 23.3 ± 5.6 y, BMI 22.7 ± 3.3 kg/m², body fat 25.6 ± 7.6%) completed the study. Subjects arrived ≥3 h post-prandial and were given two hypothetical scenarios for the following day: 1) morning rest (REST), or 2) morning rest with the addition of 1 h of hard aerobic exercise at 10:00–11:00 (EXERCISE). For each scenario subjects had to plan their lunch, to consume at 12:00, by serving themselves cheesy tomato pasta and chocolate buttons. Scenarios were randomised and separated by 5 min and foods were not consumed. EXERCISE increased total energy served by 24% (EXERCISE 3308 ± 1217 kJ; REST 2663 ± 924 kJ; P < 0.001), with increases in energy served from both pasta (+25%; P < 0.001) and chocolate buttons (+20%; P = 0.024). These results suggest aerobic exercise increases planned post-exercise energy intake, if a meal is planned in advance of exercise. Future research should examine the impact of exercise on meal planning at other meals, as well as how this behaviour impacts weight loss with exercise training.

Introduction

The most recent public health statistics suggest that the prevalence of overweight and obesity continue to rise, with 61% of UK adults currently classified as overweight or obese (Health Survey for England, 2016). Weight gain occurs due to chronic positive energy balance (i.e. energy intake greater than energy expenditure), leading to accumulation of fat in adipose tissue (Schrauwen, 2007). Increasing physical activity, particularly aerobic activity, is one method of increasing energy expenditure that has been suggested to assist with weight management (Caudwell et al., 2011). The premise of this strategy is that the accumulation of energy expended through physical activity manifests in a negative energy balance and subsequent reduction in body fat levels (Caudwell et al., 2011).

Clearly, the success of a weight loss strategy involving increased exercise will depend on the degree of compensation through the other components of energy balance (i.e. energy intake, resting energy expenditure and of physical activity; Caudwell et al., 2011). Acute exercise studies have typically reported a transient reduction in subjective appetite (Broom, Stensel, Bishop, Burns, & Miyashita, 2007; Pomerleau, Imbeault, Parker, & Doucet, 2004) and ideal portion size (Farah et al. 2012) during/after exercise, with minimal effect on subsequent energy intake compared to a resting control trial (Schubert, Desbrow, Sabapathy, & Leveritt, 2013). Whilst some studies report a small increase in absolute energy intake (i.e. total energy consumed) after exercise (Martins et al., 2007a, 2007b; Pomerleau et al., 2004; Shorten, Wallman, & Guelfi, 2009), relative energy intake (energy consumed minus energy expended through exercise/rest) is consistently reduced by exercise. Therefore, acute exercise studies suggest exercise produces an environment conducive to weight loss by increasing energy expenditure without a compensatory increase in energy intake.

However, chronic exercise interventions (i.e. ≥8 weeks) have typically not observed the anticipated weight loss that would be expected given the acute effects of exercise on relative energy intake (King, Hopkins, Caudwell, Stubbs, & Blundell, 2008; Turner et al. 2010; Wu, Gao, Chen, & van Dam, 2009). Typically, there is an initial weight loss, however, after this, the rate of weight loss attenuates or weight becomes stable over time (Curioni & Lourenco, 2005; Wu et al., 2009). Whilst there is likely a reduced energy requirement due to the reduction in body mass over time, these studies also suggest there is some alteration in the other components of energy balance to compensate in some way for the energy expended through exercise training. Given that non-prescribed physical activity energy expenditure (Turner et al., 2010) and resting metabolic rate (Lee et al. 2009; Speakman & Selman, 2003) do not appear to change with exercise training, alterations in dietary intake/eating behaviour have been suggested as the likely cause of this effect (Turner et al. 2010).

Aside from what we eat, a critical factor is how much we eat. Factors influencing portion size selection strongly affect energy intake, and therefore represent a crucial aspect of energy balance (Brunstrom, 2011). Previous studies that have investigated the relationship between exercise and energy intake have employed an ad-libitum approach to assess energy intake. In this approach, subjects are presented with a variety of food items in excess amounts and are asked to eat or drink until satiated. In day-to-day living, this type of eating occasion is relatively rare for most humans, with meals generally involving some planning of the type and/or the amount of food selected, in advance of the eating occasion (Brunstrom, 2011). Additionally, food choice is generally reduced in a laboratory environment.

Interestingly, Werle, Wansink, and Payne (2011) reported that participants who answered a series of questions related to exercise served themselves more snacks, and therefore more calories, than those in a control group whose questions were unrelated to exercise. In most cases, exercise sessions are scheduled in advance of being undertaken (i.e. individuals know that they will exercise and likely think about the exercise), meaning the size/nature of any meals prepared/cooked in advance of exercise might be influenced by the knowledge of the upcoming exercise session. However, the design of most previous exercise studies does not allow any planning behaviour in the context of exercise to be directly evaluated in advance of the session. More recently, Sim et al. (2014) reported that inactive overweight males scoring high for dietary restraint increased energy intake at a snack before exercise. These results suggest that exercise might increase energy intake (or planned energy intake) when decisions are made in advance of exercise, although the training and/or weight status of the volunteers may have influenced the results.

Therefore, the aim of this study was to examine how exercise influences meals planned for the post-exercise period of regularly exercisers by providing subjects with hypothetical exercise and rest scenarios and asking them to plan their post-exercise meal. It was hypothesised that subjects would plan to consume more energy after exercise than after rest.