Consumption of a Variety of Vegetables to Meet Dietary Guidelines for Americans' Recommendations Does Not Induce Sensitization of Vegetable Reinforcement Among Adults with Overweight and Obesity: A Randomized Controlled Trial

BACKGROUND

Food reinforcement, or the motivation to obtain food, can predict choice and consumption. Vegetable consumption is well below recommended amounts for adults, so understanding how to increase vegetable reinforcement could provide valuable insight into how to increase consumption.

OBJECTIVES

We sought to determine whether daily consumption of the Dietary Guidelines for Americans (DGA) recommendations for vegetable intake induces sensitization of vegetable reinforcement in adults with overweight and obesity.

METHODS

Healthy adults with a BMI ≥ 25 kg/m2 who consumed ≤1 cup-equivalent of vegetables/day were randomly assigned to a vegetable intervention (VI; n = 55) or an attention control (AC; n = 55) group. The VI consisted of the daily provision of vegetables in the amounts and types recommended by the DGA (∼270 g/day) for 8 weeks. Participants were followed for an additional 8 weeks to assess sustained consumption. Compliance was measured weekly by resonance Raman light-scattering spectroscopy (RRS). Vegetable reinforcement was tested at weeks 0, 8, 12, and 16 using a computer choice paradigm.

RESULTS

In the VI group, RRS intensity increased from week 0 to 8 (from 22,990 to 37,220), returning to baseline by week 16 (27,300). No change was observed in the AC group. There was no main effect of treatment (P = 0.974) or time (P = 0.14) and no treatment x time interaction (P = 0.44) on vegetable reinforcement. There was no moderating effect of sex (P = 0.07), age (P = 0.60), BMI (P = 0.46), delay discounting (P = 0.24), 6-n-propylthiouracil taster status (P = 0.15), or dietary disinhibition (P = 0.82) on the change in vegetable reinforcement.

CONCLUSIONS

These findings suggest no effects of the provision of a variety of vegetables to meet DGA recommendations for 8 weeks on vegetable reinforcement and highlight the difficulty in increasing vegetable consumption in adults. This trial was registered at clinicaltrials.gov as NCT02585102.

Negative urgency moderates reactivity to laboratory stress inductions

Impulsive personality traits refer to a group of self-reported dispositions about self-regulatory capacity, several of which have been linked to diverse forms of psychopathology. One of these is negative urgency (NUR), the propensity to act out when experiencing negative emotions, which has been linked to substance use disorders and eating disorders. However, few laboratory studies have investigated the extent to which self-reported NUR relates to an individual's in vivo emotional and behavioral responses. Harmonizing two archival data sets on alcohol and high-energy-dense (HED) food motivation, the current study investigated NUR as a moderator of reactivity to stressful situations elicited by two commonly used stress manipulations, the Trier Social Stress Test and a stress imagery induction. A sample of 148 adults was assessed for NUR, severity of alcohol misuse or binge eating, and measures of negative affect and psychophysiological arousal (i.e., heart rate and blood pressure) prior to and following one of the two manipulations. In addition, a behavioral multiple-choice procedure assessing the relative reinforcing value of alcohol or HED foods followed the manipulations. As predicted, NUR positively moderated the effects of stress induction on self-reported negative affect and relative reinforcing value, although not arousal. Individuals exhibiting elevated NUR also exhibited greater alcohol misuse, although not greater binge eating severity. These findings provide in vivo validation of the construct of NUR and its measurement using the UPPS-P Impulsive Behavior Scale. More broadly, these findings inform the understanding of deficits that are characteristic of self-regulatory disorders. (PsycINFO Database Record

The effect of a peer on VO2 and game choice in 6-10 year old children

Relative to sedentary video games (e.g., Playstation 2®), playing physically active video games (e.g., Nintendo Wii Sports Boxing®) significantly increases caloric expenditure in children. Studies have demonstrated that the presence of a peer increases physical activity in children. We sought to determine if children would expend more energy and find playing the “exergame” (Wii) more motivating than the sedentary video game (Playstation 2) when with a peer. Seventeen children (age 8.5 ± 0.4 years) rested, played the sedentary video game and “exergame” for 10 min each, in two conditions: one in which the children rested/played the games alone (alone condition) and another in which they played with a peer (peer condition). Oxygen consumption (VO₂), and liking (visual analog scale) was assessed for each 10-min condition. After three 10-min resting/gaming conditions, motivation was assessed using a relative reinforcing value task in which children performed computer mouse presses to gain additional access for either the sedentary video game or “exergame.” VO₂ was greater (p < 0.001) during “exergame” play (mean = 12.17 ± 4.1 ml·kg⁻¹·min⁻¹) vs. rest (mean = 5.14 ± 1.46 ml·kg⁻¹·min⁻¹) and the sedentary video game (mean = 5.83 ± 2.1 ml·kg⁻¹·min⁻¹). During the peer condition, there were no significant differences (p > 0.05) in VO₂ relative to the alone condition. In an exploratory analysis boys exhibited a greater (p = 0.02) increase in VO₂ from rest to “exergame” (Δ 9.0 ± 3.7 ml·kg⁻¹·min⁻¹), relative to girls (Δ 4.9 ± 2.9 ml·kg⁻¹·min⁻¹). Boys showed a significantly greater increase (p = 0.05) in VO₂ from the resting condition to “exergame” in the presence of a peer (Δ 11.1 ± 5.3 ml·kg⁻¹·min⁻¹) vs. the alone condition (Δ 6.8 ± 3.1 ml·kg⁻¹ ·min⁻¹). Liking was significantly (p < 0.001) greater for “exergame” (7.7 ± 1.9 cm) and the sedentary video game (8.3 ± 1.3 cm) relative to rest (4.0 ± 2.8 cm). Motivation for “exergame” significantly decreased (p = 0.03) from alone (340.8 ± 106.8 presses) to the peer condition (147.8 ± 81.6 presses).

Conclusion: VO₂ was greater during “exergame” play relative to the sedentary video game. The presence of a peer did not increase VO₂ during “exergame” play. Surprisingly, the presence of a peer decreased children's motivation to play “exergame” vs. the sedentary video game.