The Challenge of Stimulus Control: a Comment on Poelman et al.

Stimulus control interventions attempt to reduce unhealthy behavior (or increase healthy behavior) by identifying and modifying environmental factors that repeatedly trigger that behavior [1]. In the context of weight management, modifying the food environment has been a focus given the omnipresence of energy-dense foods in the home, workplace, and marketplace. Poelman and colleagues conducted a randomized trial of an intervention that aimed to reduce BMI by educating participants about portion control and the environmental triggers that lead to overconsumption [2]. Unfortunately, their intervention showed a very modest and short-lived effect on body mass index.

A key intermediate outcome of this trial was participants’ use of 32 portion control strategies, including buying food packaged in small portions, keeping tempting foods out of the home, keeping leftovers off the table during a meal, splitting restaurant meals, and avoiding snack tables at parties. Many of these portion control strategies involve stimulus control, meaning they attempt to manage stimuli that trigger overeating behavior. Stimulus control strategies capitalize on individuals’ capacity to exercise inhibitory control over their food choices when palatable food is not immediately available. The challenge of stimulus control strategies in a toxic food environment is that palatable foods are omnipresent. For example, grocery shopping habits are often targeted because it might seem easier to resist the temptation of a favorite treat when it is packaged on the supermarket shelf than when it is in a bowl on the kitchen counter. However, supermarkets are stocked with a wide variety of highly palatable, heavily processed, ready-to-eat foods which may significantly burden inhibitory control in ways that make the difference between this environment and the candy bowl possibly inconsequential. Crucial to stimulus control strategies is implementing them when inhibitory control is strongest. A greater understanding is needed about factors affecting an individual's inhibitory control across different settings and how best to employ stimulus control strategies in the individual's food environment, including home, food stores, and restaurants.

Other portion control strategies that were included in the intervention tested by Poelman and colleagues did not rely exclusively on stimulus control but similarly require significant inhibitory control (e.g., leaving food on the plate during meals, not snacking on ingredients when cooking) [2]. These strategies are to be implemented at the point when tempting food is immediately available. Direct exposure to palatable food activates the brain's reward circuitry and increases the motivational drive to eat, even in the absence of physical hunger [3]. Thus, the capacity for inhibitory control may be most compromised when we are preparing and eating a meal. Implementing portion control strategies in these contexts is equivalent to instructing a participant to simply exercise willpower. Essentially, advising people to just resist an unhealthy temptation ignores the very processes that make this request difficult to follow.

According to behavior analytic theory, a stimulus triggers a behavior given a history of that behavior being reinforced in the presence of that stimulus. To reduce or eliminate a behavior from occurring, access to the stimulus must be revoked (e.g., individual no longer has access to settings that contain tempting food), its reinforcing value decreased (e.g., tempting food becomes less palatable), the cost of behavior increases, or avoidance behavior is immediately reinforced (e.g., individual receives immediate rewards for abstaining). Some of these approaches may be impractical such as making palatable food less palatable, whereas others may be more practical to implement such as junk food taxes [4]. Stimulus control strategies that simply encourage people to avoid the stimulus would likely have minimal impact to the extent that they do nothing to reduce the strength or presence of the stimulus or reinforce avoidance behavior. Weight loss is a reinforcing consequence of reducing palatable food consumption, but it is heavily delayed and has variable probability given that it depends on a multitude of behaviors. Stimulus control interventions have had good efficacy for changing behavior in children because parents can enforce environmental changes that affect their children's habits [5]. For adults, the challenge to individual-level stimulus control interventions is that adults are the gatekeepers of their very own environments.

Effective stimulus control strategies in a food environment characterized by omnipresent naturally reinforcing stimuli are challenging to design, but are very much needed. Poelman and colleagues work is a step in the right direction in its focus on assisting people to navigate their environments, but may have fell short in terms of the need for greater attention to the aforementioned processes by which stimulus control strategies can be strengthened. In addition, future work should devise novel strategies to enhance individual-level stimulus control and portion control interventions by eliminating the individual's access to triggering environments in which they have diminished inhibitory control (e.g., grocery stores, restaurants), reducing the relative reinforcing value of palatable foods, increasing the cost of energy-dense food, and/or rewarding avoidance behavior.

Author notes

1

Conflict of Interest Dr. Pagoto is on the advisory board of Empower Fitness. Dr. Appelhans has no conflict of interest to disclose.

© The Society of Behavioral Medicine 2014