Altering the availability of healthier vs. less healthy items in UK hospital vending machines: a multiple treatment reversal design

Rachel Pechey,Theresa M Marteau,Emma Cartwright,Holly Jenkins

doi:10.1186/s12966-019-0883-5

Abstract

BackgroundAltering the availability of healthier or less-healthy products may increase healthier purchases, but evidence is currently limited. The current study aimed to investigate the impact of altering the absolute-and-relative availability of healthier and less-healthy products – i.e. simultaneously altering the number of options available and the proportion of healthier options – in hospital vending machines.MethodsAn adapted multiple treatment reversal design was used, altering products available in ten vending machines serving snack foods and/or cold drinks in one English hospital. Machines were randomised to one of two sequences for the seven 4-week study periods: ABCADEA or ADEABCA. In Condition A (study periods 1, 4 and 7) the proportions of healthier products were standardised across all machines, so that 25% of all snack slots and 75% of drink slots were healthier. In Condition B, 20% of vending machine slots were emptied by removing less-healthy products. In Condition C, the empty slots created in Condition B were filled with healthier products. Conditions D and E were operationalised in the same way as B and C, except healthier products were removed in D, and then less-healthy products added in E. Sales data were obtained from machine restocking records. Separate linear mixed models were conducted to examine the impact of altering availability on energy purchased (kcal) from (i) snacks or (ii) drinks each week, with random effects for vending machine.ResultsThe energy purchased from drinks was reduced when the number of slots containing less-healthy drinks was decreased, compared to standardised levels (− 52.6%; 95%CI: − 69.3,-26.9). Findings were inconclusive for energy purchased from snacks when less-healthy snack slots were reduced (− 17.2%; 95%CI: − 47.4,30.5). Results for altering the number of slots for healthier drinks or snacks were similarly inconclusive, with no statistically significant impact on energy purchased.ConclusionsReducing the availability of less-healthy drinks could reduce the energy purchased from drinks in vending machines. Further studies are needed to establish whether any effects might be smaller for snacks, or found with higher baseline proportions of healthier options.

Highlights

Altering the availability of healthier or less-healthy products may increase healthier purchases, but evidence is currently limited
The current study investigated the impact of altering the absolute-and-relative availability of healthier and less healthy foods and cold beverages in vending machines in one National Health Service (NHS) hospital that was part of a larger Trust
In Condition A, the proportions of healthier products were standardised across all vending machines so that 75% of all drinks were healthier and 25% of snacks. (The higher standardised proportion for drinks relative to baseline was chosen so that the proportions of healthier to less healthy would mirror those for snacks, but in reverse.) In Condition B, 20% of vending machine slots were emptied by removing less-healthy products

Summary

Introduction

Altering the availability of healthier or less-healthy products may increase healthier purchases, but evidence is currently limited. The current study aimed to investigate the impact of altering the absolute-and-relative availability of healthier and less-healthy products – i.e. simultaneously altering the number of options available and the proportion of healthier options – in hospital vending machines. Availability is one of the top three interventions suggested in the McKinsey Global Institute report [2] as having the highest likely impact across the population, and a Cochrane review of the impact of availability interventions suggests that such interventions can reduce selection and consumption of targeted food products – albeit limited by the quality and quantity of the included studies [3]. A report by Public Health England suggested that introducing healthier products in hospital vending machines might reduce energy purchased from drinks and snacks – the study found increased sugar was purchased from snacks [6]. A review of worksite interventions [7] identified only two studies focused on increasing the availability of healthier foods as a single intervention, both showing introducing fruit baskets led to increased fruit intake [8, 9]

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