Food Reinforcement, Attentional Bias, and Inhibitory Control as Mechanisms of Energy Compensation With Exercise

Over 70% of adults in the US are overweight or obese putting them at risk for a multitude of comorbidities including cardiovascular disease, hypertension, diabetes, dyslipidemia, metabolic syndrome, and certain cancers. Greater mortality rates with obesity have estimates of life expectancy reduced by 6-7 years with up to 300,000 deaths attributed to obesity annually in the US. Obesity treatment has therefore emerged as a prime focus of health care.

Increasing physical activity and energy expenditure is a universal recommendation for weight control, with exercise becoming the most prevalent, economical, and health-promoting treatment option for obesity.

Unfortunately, weight loss from an exercise program is often disappointing, and greater amounts of exercise may not always promote additional weight loss. An increasing body of evidence indicates individuals' concerted efforts to achieve weight loss through exercise are stymied by a coordinated set of compensatory responses working to maintain energy balance, conserving energy to ensure the energetic needs of vital organs are met. The primary compensatory response working to maintain energy homeostasis and thus opposing weight loss from an exercise-induced energy deficit is an increased drive for greater energy intake. This is often independent of hunger, as single bouts of exercise typically do not result in changes in appetite, food intake, or appetite- regulating hormones, while long-term exercise can actually improve the satiety response to a meal. The motivational aspects of eating, termed the reinforcing value of food, is a strong predictor of body weight and energy intake independent of hunger, although not previously studied as an important factor in energy compensation with exercise. Food reinforcement is developed by instigating a greater attentional processing towards food, termed attentional bias. These behavioral constructs are controlled by the central dopamine system, which mediates the rewarding aspects of reinforcing behaviors (such as eating) and is a more powerful driver of behavior than affective responses. Overeating occurs when the motivational wanting of food exceeds the capacity of inhibitory control for eating. As such, individuals with lower inhibitory control are more susceptible to the reinforcing aspects of food, and more likely to over-consume highly reinforcing, energy dense foods. With additional evidence eating and exercise behaviors share similar neuro-behavioral pathways possibly explaining why exercise can promote feeding in animal models, it would be of great interest to determine the influence exercise may have on food reinforcement, attentional bias, and inhibitory control for food cues in humans.

Our long-term goal is to reduce the incidence and improve the outcomes of obesity by developing interventions to attenuate compensation for the energy expended through exercise thereby improving exercise as a weight loss and weight loss maintenance strategy. The overall objectives of the current proposal are to 1) evaluate whether an acute bout of exercise alters food reinforcement, attentional bias and inhibitory control for food cues, and 2) assess a potential sex effect in this response. Our central hypothesis is that exercise training will evoke greater food reinforcement and attentional bias for food cues while reducing inhibitory control as a mechanism to promote greater energy intake in effort to maintain energy homeostasis. Our hypothesis has been formulated based on our preliminary data demonstrating a large (~1,000 kcal per week) compensatory response to a 12-week exercise intervention that could not be explained by changes in resting energy expenditure, physical activity outside the exercise intervention, or hormonal mediators of appetite. This compensatory response was observed across two different studies using various exercise doses, indicating a remarkable consistency in this compensatory response. Previous research in animal models have demonstrated exercise facilitates eating, with evidence of shared neuro-behavioral pathways between eating and exercise reward that may explain this connection. These behavioral constructs influencing energy intake have not been considered as mechanisms for energy compensation and likely contribute to the unexplained compensatory response we have previously observed. The rationale for this project is that with greater knowledge of the mechanisms behind energy compensation, future interventions may be designed that attenuate this response to improve exercise's utility as a weight loss strategy. To achieve the overall objectives, we will pursue the following specific aim and exploratory aim in obese, sedentary individuals, the population in greatest need for effective weight loss treatment: Specific Aim: Demonstrate changes in food reinforcement, attentional bias and inhibitory control for food cues after an acute bout of exercise. Based on our preliminary data and previous literature demonstrating exercise may increase food reward, our working hypothesis is an acute bout of exercise will cause food to be more reinforcing, increase attentional bias for food cues, and decrease inhibitory control for food cues.

Exploratory Aim: We will explore whether sex moderates these responses. Others have demonstrated sex differences in food reinforcement, although the role sex plays in this response to exercise is unknown.