How and why does discretionary food consumption change when we promote fruit and vegetables? Results from the ShopSmart randomised controlled trial

© The Authors 2019. Objective:The present study aimed to identify whether discretionary food consumption declined in an intervention focused primarily on promoting fruit and vegetable consumption. We also aimed to identify potential mediators explaining intervention effects on discretionary food consumption.Design:Secondary analysis of data from the ShopSmart study, a randomised controlled trial involving a 6-month intervention promoting fruit and vegetable consumption. Linear regression models examined intervention effects on discretionary food consumption at intervention completion (T2). A half-longitudinal mediator analyses was performed to examine the potential mediating effect of personal and environmental factors on the association between the intervention effects and discretionary food consumption. Indirect (mediated) effects were tested by the product of coefficients method with bootstrapped se using Andrew Hayes' PROCESS macro for SPSS.Setting:Women were recruited via the Coles FlyBuys loyalty card database in socio-economically disadvantaged suburbs of Melbourne, Australia.Participants:Analyses included 225 women (116 intervention and 109 control).Results:Compared with controls, intervention participants consumed fewer discretionary foods at T2, after adjusting for key confounders (B = -0·194, 95 % CI -0·378, -0·010 servings/d; P = 0·039). While some mediators were associated with the outcome (taste, outcome expectancies, self-efficacy, time constraints), there was no evidence that they mediated intervention effects.Conclusions:The study demonstrated that a behavioural intervention promoting fruit and vegetable consumption among socio-economically disadvantaged participants was effective in reducing discretionary food intake. Although specific mediators were not identified, researchers should continue searching for mechanisms by which interventions have an effect to guide future programme design.