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

Authors: Casperson, Shanon; JAHNS, LISA - Former ARS Employee; TEMPLE, JENNIFER - University Of Buffalo; APPLETON, KATHERINE - Bournemouth University; Roemmich, James

Submitted to: The American Journal of Clinical Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/5/2021
Publication Date: 3/23/2021
Citation: Casperson, S.L., Jahns, L., Temple, J.L., Appleton, K., Roemmich, J.N. 2021. 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. American Journal of Clinical Nutrition. 151:1665-1672. https://doi.org/10.1093/jn/nxab049.
DOI: https://doi.org/10.1093/jn/nxab049

Interpretive Summary: Among the US adult population, vegetable intake is well below amounts recommended by the Dietary Guidelines for Americans (DGA). Using obese men and women whose vegetable intake is considered low (=1 serving per day), we conducted an intervention study to determine whether increasing vegetable intake to meet DGA recommendations can change their motivation to eat vegetables. We used a computer choice paradigm to measure the relative reinforcing value (RRV) of vegetables before and after an 8-week intervention and then followed the participants for another 8 weeks to see if they continued to eat the recommended amounts of vegetables on their own. The RRV of vegetables was measured before and after the 8-week intervention and then again at weeks 12 and 16 of the follow-up period. We found that the RRV of vegetables did not change or was decreased for most of the participants. However, for 29% of the participants the RRV of vegetables was increased. Participant characteristics that are thought to contribute to low vegetable intake such as gender, weight, and if they are sensitive to bitter taste were also tested. There were no differences in these characteristics between the participants for which the RRV of vegetables increased, decreased or stayed the same. These findings highlight the difficulty of getting Americans to eat more vegetables.

Technical Abstract: The relative reinforcing value (RRV) of a food predicts choice and consumption of that food. Vegetable consumption is well below recommended amounts for adults, so understanding how to increase the RRV of vegetables will provide valuable insight on how to increase their consumption. Objective: To determine whether daily intake of Dietary Guidelines for Americans (DGA)-recommended amounts of vegetables increases the RRV of vegetables in adults with overweight and obesity. Design: Healthy adults age 40±15y with a BMI of 34±7 kg/m2 and consuming =1 serving of vegetables/day participated in this community-based, 16-week, parallel-group, non-blinded trial. Participants were randomly assigned to a vegetable intervention (n=55) or an attention control (n=55) group. The vegetable intervention consisted of daily exposure to 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). RRV of vegetables was tested at weeks 0, 8, 12 and 16 using a computer choice paradigm. A priori secondary analyses examined the potential moderating effect of sex, BMI, delay discounting, 6-n-propylthiouracil tasting status, and disinhibition on the RRV of vegetables and sustained consumption. Results: Repeated exposure to DGA-recommended amounts of vegetables did not increase RRV of vegetables and there was no moderating effect of the a priori potential moderators. Incentive sensitization to vegetables occurred in 15 (29%) of the intervention participants; however, vegetable consumption returned to baseline amounts at the 8-week follow-up in this subgroup. Conclusions: These findings highlight the difficulty in increasing vegetable consumption in adults and suggest that efforts should be guided towards reducing the RRV of energy-dense foods rather than increasing the RRV of nutrient-dense foods to shift behavioral choice toward healthier food options.