Obesity is a significant and growing public health concern. The current front-line therapy involves comprehensive lifestyle intervention focused on dietary modification, physical activity, and behavior change strategies. Weight loss outcomes are largely a function of sustained behavioral adherence to any reduced-energy diet, and most dietary lapses are precipitated by temptation from palatable food. Understanding the neurobehavioral processes underlying temptation can inform the development of more effective weight management strategies.
The Challenge of Lifestyle Interventions
Roughly 50% of lifestyle intervention participants lose at least 5-10% of initial body weight, which is the minimum benchmark for conferring clinically meaningful improvements in cardiometabolic risk factors. The remaining half of lifestyle intervention participants are nonresponders with respect to this outcome. In addition to high nonresponse rates, relapse is common (perhaps the norm). About one-third to one-half of lost weight is regained within one year of treatment discontinuation. Even with ongoing, long-term intervention, only about 3.2 kg or 4-5% of lost weight is maintained. One path toward improved weight loss outcomes involves strengthening intervention strategies to help participants manage temptation from the highly palatable but unhealthy foods that permeate modern society.
The Dual Systems of Eating Regulation
Eating is regulated by two distinct but interconnected neurobehavioral systems: a homeostatic system and a reward-based system. In the homeostatic system, food is a component of a physiological-behavioral homeostatic feedback loop that governs energy balance. In contrast, the reward system influences eating in response to the sensory experience of food. Two dimensions of reward have been distinguished in the literature: liking and wanting. Liking reflects the hedonic aspect of reward and applies to the sensory pleasure associated with eating palatable food. Wanting, in contrast, manifests as appetitive motivation, desire, craving, and temptation; it is the dimension of reward that challenges self-control. Wanting underlies engagement in a variety of appetitive behaviors, including sexual activity, gambling, and substance abuse. When applied to food, wanting provides the motivational drive that supports adaptive foraging and hunting behaviors in environments of scarcity, but contributes to overeating in modern environments characterized by an abundance of hyper-palatable foods that can be obtained with minimal effort. Though liking and wanting may not be phenomologically distinct in most day-to-day human experiences, it is increasingly recognized that reward, rather than energy homeostasis, is the primary driver of overeating in modern society. Individual differences in food reward processing, reflected in a variety of behavioral and biological measures, are implicated in obesity risk.
Neurobehavioral Processes During Temptation
The influences of several neurobehavioral processes emerge during the experience of temptation: reward-driven attentional biases, temporal discounting, and the cold-hot empathy gap.
Reward-Driven Attentional Biases
Reward is a strong modulator of cognitive control, having both bottom-up and top-down influences of reward on attention allocation. Motivationally salient stimuli in the environment preferentially attract reactive attention, and conversely, one’s motivational state affects the extent to which attention is proactively directed to seeking out reward-related stimuli. As a rewarding stimulus, food elicits several forms of attentional bias, including greater susceptibility to distraction by food cues, more rapid detection of food cues in the visual field, and greater difficulty disengaging attention from food cues. These biases are enhanced in a state of hunger or food craving, particularly for palatable, energy-dense foods. Attentional biases may potentiate the appetitive pursuit of rewards by keeping individuals locked onto rewarding stimuli until they are consumed. Thus, for obese individuals participating in lifestyle interventions, palatable food may act as a “motivational magnet” that monopolizes attention and triggers lapses in diet adherence.
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Temporal Discounting
Mechanistically, engaging in health behaviors often involves pursuing the more valuable, long-term rewards associated with wellness over immediate gratification from various temptations. This dynamic characterizes healthy eating and weight control, abstaining from substance use and risky sexual activity, and other health behaviors. Yet these choices are rarely straightforward, even for those who value their future health. Humans discount the value of future rewards relative to opportunities for immediate gratification, a process known as temporal discounting. Delayed rewards are discounted in value as a hyperbolic function of time such that the desire for a reward spikes just before it is received. As a result, an individual presented with the choice between two future rewards may initially prefer the more highly valued option, but experience a preference reversal if the less preferred reward becomes available immediately. Due to hyperbolic temporal discounting, an individual’s preference for a large, delayed reward (e.g., weight control) can reverse if a smaller but immediate reward (e.g., dessert) becomes available. These preference reversals (occurring at the intersection of the two valuation curves), are characteristic of impulsive, short-sighted decisions. Most dietary lapses can be interpreted as preference reversals. In general, the most palatable, rewarding foods are high in calories, fat, salt, and sugar, and are poor in nutrients, which places immediate gratification from food in direct opposition to healthy eating and weight control. A dieter generally prefers weight loss to food reward when both options are considered as future outcomes. However, relative to the point of decision, the weight loss benefits of individual food choices are perpetually perceived as occurring in the future, whereas gratification from food is immediate.
The Cold-Hot Empathy Gap
“Hot” visceral states such as hunger, thirst, sexual arousal, and craving are characterized by increased wanting of stimuli (e.g., food, water, sexual stimulation, drugs) that can resolve these drives. Yet humans have difficulty anticipating the often powerful effects of visceral states (including temptation) on their decisions and behaviors. This inability to “empathize” with one’s self in a different visceral state plays out in two ways. The hot-cold empathy gap is apparent when individuals in a hot, motivated state overestimate the degree to which they will value a reward in a non-motivated, neutral, “cold” state. Conversely, the cold-hot empathy gap describes the tendency of an individual in a cold state to underestimate the impact of future hot visceral states on their decisions and behavior. Just as hungry subjects overvalue foods that they will consume in the future, satiated subjects underestimate the value food will have to them in the future when they are hungry. Similar examples of cold-hot empathy gaps have been documented during sexual arousal, drug craving, and other visceral states.
Temptation Management Strategies: Resistance vs. Prevention
The shifting neurobehavioral profile of dieters from cold to hot (tempted) states underscores the importance of distinguishing between intervention strategies focused on resisting temptation while it is experienced, and those focused on avoiding temptation altogether. In contrast to temptation resistance strategies, temptation prevention strategies focus on avoiding or minimizing temptation. For example, stimulus control strategies involve identifying and modifying environmental factors that trigger problem behaviors, such as removing tempting foods from the home to prevent overeating. Other interventions emphasize scheduling and planning as strategies to manage temptation. The effectiveness of temptation prevention strategies may hinge on whether they are implemented in a cold state. Both temptation resistance and prevention strategies are commonly featured in lifestyle interventions; however, their uptake and utilization by subjects and their impact on diet adherence (independent of the overall intervention package) have not been characterized.
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