Overweight children find food more reinforcing and consume more energy than do nonoverweight children

BACKGROUND

The reinforcing value of food is a reliable index of motivation to eat and energy intake. Obese adults find food more reinforcing than do nonobese adults.

OBJECTIVE

The present study was designed to assess whether the relative reinforcing value of food differs as a function of weight status in 8-12-y-old children and whether the relative reinforcing value of food differs depending on the types of available nonfood alternatives.

DESIGN

The reinforcing value of pizza (experiment 1) or snack foods (experiment 2) was measured on progressive ratio schedules of reinforcement in nonoverweight and overweight children. Experiment 2 also compared the relative reinforcing value of food and 2 nonfood alternatives: time to spend playing a hand-held video game or time to spend reading magazines or completing word searches or mazes.

RESULTS

In both experiments, overweight children found food more reinforcing and consumed more energy than did their leaner peers. In experiment 2, the relative reinforcing value of food versus sedentary activity was higher in overweight children, but lower in nonoverweight children, regardless of the type of alternative activity available.

CONCLUSIONS

These results show that overweight children find food more reinforcing than do nonoverweight children. This individual difference was replicated in different experiments using different types of foods and food alternatives. These studies provide support for studying food reinforcement as a factor associated with overweight and obesity.

Dietary variety impairs habituation in children

OBJECTIVE

The purpose of these studies was to test the hypothesis that dietary variety decreases the rate of habituation and increases energy intake in children.

DESIGN

In Experiment 1, salivation in response to the same or a variety of food cues was measured followed by consumption of the study food(s). In Experiment 2, children responded in a computer task to earn points for the same or a variety of low or high energy density foods, which were then consumed.

MAIN OUTCOME MEASURES

Salivation, number of responses, and energy intake were measured.

RESULTS

Participants in the same groups habituated faster than those in the variety groups (p = .05), and in Experiment 2, the effect of variety was independent of energy density. Participants in the variety groups also consumed more energy than those in the same groups in both experiments (p = .05).

CONCLUSIONS

Dietary variety disrupted habituation and increased energy intake in children. In addition, the response to dietary variety was independent of energy density, suggesting that increasing variety of low energy density foods may increase consumption.

Dietary variety impairs habituation in children

OBJECTIVE

The purpose of these studies was to test the hypothesis that dietary variety decreases the rate of habituation and increases energy intake in children.

DESIGN

In Experiment 1, salivation in response to the same or a variety of food cues was measured followed by consumption of the study food(s). In Experiment 2, children responded in a computer task to earn points for the same or a variety of low or high energy density foods, which were then consumed.

MAIN OUTCOME MEASURES

Salivation, number of responses, and energy intake were measured.

RESULTS

Participants in the same groups habituated faster than those in the variety groups (p = .05), and in Experiment 2, the effect of variety was independent of energy density. Participants in the variety groups also consumed more energy than those in the same groups in both experiments (p = .05).

CONCLUSIONS

Dietary variety disrupted habituation and increased energy intake in children. In addition, the response to dietary variety was independent of energy density, suggesting that increasing variety of low energy density foods may increase consumption.

Habituation and within-session changes in motivated responding for food in children

Within-session decreases in instrumental responding to obtain food, consistent with habituation, have been reliably demonstrated in adults and children. This study tested the hypothesis that within-session decreases in instrumental responding for food are due to habituation rather than satiation. Thirty-eight 8-12-year-old children performed a computer-based operant task to earn points toward access to potato chips for 20 min, and for chocolate candies for the final 6 min of the session. Portion size of the food reinforcer (75 kcal vs 225 kcal) and food consumption (consumption/no consumption). There was no difference in the rate of response decrease between the two portion size conditions. Both the consumption and non-consumption groups showed response decelerations during the first 20 min, with responses in the consumption group decreasing at a faster rate. When the novel food was presented, participants in all conditions recovered responding. Although satiation may contribute to reductions in motivated responding for food when food is consumed, habituation provides a more complete explanation for the results observed in this study.

Overweight children habituate slower than non-overweight children to food

We have shown that physiological and behavioral responses habituate to food stimuli and recover when novel stimuli are presented. In addition, physiological responses in obese adults habituate slower to repeated food stimuli than those in non-obese individuals, which is related to greater energy intake. The purpose of this study was to test the hypothesis that instrumental responding in overweight children habituates slower to food cues than in their non-overweight peers. Children were provided the opportunity to work for access to cheeseburger for 10 2-min trials, followed by French fries for 3 2-min trials. Results showed that children who had a body mass index (BMI) at or above the 85th BMI percentile (at risk for overweight; n=17) habituated slower than those with a BMI percentile less than the 85th BMI percentile (non-overweight; n=17). Response recovery to French fries did not differ between groups. Overweight children consumed significantly more grams of food and more energy than non-overweight children. When taken together, these data show that habituation may be an important individual difference characteristic that differentiates overweight from non-overweight children. Implications of this for prevention and treatment of obesity are discussed.

Television watching increases motivated responding for food and energy intake in children

BACKGROUND

Sedentary activities, such as watching television, may disrupt habituation to food cues, thereby increasing motivation to eat and energy intake.

OBJECTIVE

These experiments were designed to examine the effect of television watching on habituation of ingestive behavior in children.

DESIGN

In experiment 1, all children worked for access to cheeseburgers in trials 1-7 (habituating stimulus). In trials 8-10, children in the control group continued to work for cheeseburgers without any dishabituating stimuli, whereas children in the other groups received either a novel food (French fries) or television as dishabituating stimuli. Responding for food and amount of food eaten were measured. In experiment 2, all children had access to 1000 kcal of a preferred snack food. One group watched a continuous television show, and the control groups either watched no television or watched a repeated segment of a television show, which controls for the television stimulus but requires reduced allocation of attention.

RESULTS

In experiment 1, both the novel food and the television watching groups reinstated responding for food (P = 0.009) and increased the amount of energy earned (P = 0.018) above the level of the control subjects. In experiment 2, the continuous television group spent more time eating (P < 0.0001) and consumed more energy than the no television and the repeated segment groups (P = 0.007).

CONCLUSION

These experiments show that television watching can dishabituate eating or disrupt the development of habituation, which may provide a mechanism for increased energy intake associated with watching television.

Habituation and recovery of salivation and motivated responding for food in children

Salivary responses habituate to repeated presentations of food cues, and these responses recover when new food stimuli are presented. Research suggests that within-session changes in motivated responding for food may also habituate, and motivated responding may, therefore, recover when new foods are presented. The purpose of this study was to evaluate similarities in the pattern of salivation and motivated responding for a cheeseburger stimulus in children, followed by either a novel stimulus (French fries) or another cheeseburger trial. The order of the task (salivation or motivation) was counterbalanced over days. Salivation and motivated responding for cheeseburger were reliably reduced over seven trials, and responses recovered after presentation of French fries on trial 8. Random regression models showed a significant relationship between the rate of change in motivated responding and salivation. These results provide additional support for similarities in processes that regulate salivation and motivated responding for food and strengthen support for the hypothesis that changes in motivated responding can be understood by habituation theory.

Effects of allocation of attention on habituation to olfactory and visual food stimuli in children

Responding to food cues may be disrupted by allocating attention to other tasks. We report two experiments examining the effects of allocation of attention on salivary habituation to olfactory plus visual food cues in 8-12-year-old children. In Experiment 1, 42 children were presented with a series of 8 hamburger food stimulus presentations. During each intertrial interval, participants completed a controlled (hard), or automatic (easy) visual memory task, or no task (control). In Experiment 2, 22 children were presented with 10 presentations of a pizza food stimulus and either listened to an audiobook or no audiobook control. Results of Experiment 1 showed group differences in rate of change in salivation (p=0.014). Children in the controlled task did not habituate to repeated food cues, while children in the automatic (p<0.005) or no task (p<0.001) groups decreased responding over time. In Experiment 2, groups differed in the rate of change in salivation (p=0.004). Children in the no audiobook group habituated (p<0.001), while children in the audiobook group did not habituate. Changes in the rate of habituation when attending to non-food stimuli while eating may be a mechanism for increasing energy intake.