Plain English Summary
Background and study aims:
People from disadvantaged communities tend to eat fewer fruits and vegetables and more high-calorie foods; they also benefit less from programs that teach people how to actively change their behaviour. Cognitive resources (a set of mental processes involved in planning and regulating thoughts and behaviour) are reduced by years spent living in poverty in childhood. Therefore, an alternative method that does not rely on cognitive resources is needed to improve intake of fruit and vegetables and reduce intake of high-calorie foods in disadvantaged communities. Making changes to the environment, such as placing food further away, is thought to change people’s behaviour unconsciously, as people generally eat more of a food when it is placed within reach. There is a need for higher quality studies of this food distance effect, specifically focusing on whether this effect occurs for healthy and unhealthy food options when they are provided at the same time at different distances. The research team previously conducted two studies which looked only at the placement of an unhealthy food option. This study will improve on the methods of the earlier studies however, by providing participants with two food options, one healthy and unhealthy, which is more similar to a real-world food environment where people actively make choices between options. The aim of this study is to assess whether placing unhealthy food further away discourages consumption of that food when a healthy food option is also available either at the same distance or closer.
Who can participate?
Healthy adults who live in Cambridge and surrounding areas.
What does the study involve?
Participants are randomly allocated into one of four groups. In each group, the participants are provided with two bowls of snack food placed at varying distances either near at 20cm or far at 70cm relative to one another during a 10 minute “relaxation break”. In the first group, the healthy food is placed near and the unhealthy food far, in the second group, the unhealthy food is near and the healthy food far. In the third group both foods are placed near while in the fourth group both foods are placed far from the participant. All participants are asked to memorise a string of digits to induce cognitive load at the beginning of the session, which they will recall at the end. Participants also complete the Stroop task (a task which involves reading the names of colours which are written in a different colour) before memorising number and after the relaxation break to measure cognitive resources. At the end of the session, they complete questionnaires about hunger, liking for the snacks and other measures related to the food.
What are the possible benefits and risks of participating?
There are no direct benefits for participants; however the study will help to provide information about ways of influencing food choice and diet that can be applied to further research. There are no risks of participating in the study.
Where is the study run from?
The Behaviour and Health Research Unit, University of Cambridge (UK)
When is the study starting and how long is it expected to run for?
October 2016 to June 2017
Who is funding the study?
1. Medical Research Council (UK)
2. NIHR Senior Investigator Award (UK)
3. Department of Health Policy Research Programme (UK)
Who is the main contact?
Professor Theresa Marteau
The effect of proximity on consumption of healthy and unhealthy food: an experimental study in a general population with low cognitive resource
1. A higher proportion of participants will take each food when it is proximal compared to when it is distal
2. The proportions of participants taking each food will be equivalent at each given distance for both healthy and unhealthy food
3. A higher proportion of participants will take a near healthier food when an unhealthier food is far compared to when the unhealthier food is at the same distance
Cambridge Psychology Research Ethics Committee, 19/12/2016, ref: PRE.2016.088
Primary study design
Secondary study design
Randomised controlled trial
Patient information sheet
See additional files
Participants are told they will be taking part in a relaxation and memory study so that the snack foods can be placed without making participants aware that the study is assessing eating behaviour (knowing this may affect whether they eat in the study). Participants are fully debriefed at the end of the session. Participants are randomly allocated to one of four conditions where food is provided during a 10 minute relaxation break.
1. Healthy food proximal, unhealthy food distal
2. Unhealthy food proximal, healthy food distal
3. Both foods proximal
4. Both foods distal
Two food bowls are placed at the same time varying at two different distances from the participant’s position. When a bowl is proximal, it is placed 20cm from the right hand of the participant and when the bowl is distal, it is placed 70cm from the right hand of the participant.
Chocolate M&Ms (without peanuts) are provided as the unhealthy snack option and fruit is provided as the healthy snack option.
All participants are asked to memorise a set of digits before the relaxation break to induce cognitive load, which they will recall at the end of the session. The Stroop task is completed before the relaxation break to record baseline cognitive resource, and after the break to check the cognitive load manipulation.
Primary outcome measure
Proportion of participants taking any of either snack food, measured as any difference in bowl weight from before to after the participant is exposed to the snacks.
Secondary outcome measures
1. Mean amount of each snack food consumed is measured as the difference in bowl weight from before to after the participant is exposed to the snacks
2. Executive function, measured using the Stroop task (Stroop, 1935) before exposure to the snack food
3. Ratings of perceived effort to obtain the snacks and salience of the snacks, collected using a questionnaire following exposure to the snack food
4. The proximity effect is measured by the difference in intake of the snacks at each given distance after the relaxation break. This difference in intake is compared before and after excluding participants who move the bowl.
Overall trial start date
Overall trial end date
Reason abandoned (if study stopped)
Participant inclusion criteria
1. Adults aged over 18 years
2. Cambridgeshire and surrounding areas
Target number of participants
Participant exclusion criteria
Any allergies or intolerance to food relevant to the study.
Recruitment start date
Recruitment end date
Countries of recruitment
Trial participating centre
The Behaviour and Health Research Unit
University of Cambridge Institute of Public Health Forvie Site Robinson Way
Medical Research Council
Funding Body Type
Funding Body Subtype
NIHR Senior Investigator Award
Funding Body Type
Funding Body Subtype
Department of Health Policy Research Programme
Funding Body Type
Funding Body Subtype
Results and Publications
Publication and dissemination plan
Planned publication of the main study results in a high-impact factor journal.
IPD Sharing plan:
The current data sharing plans for the current study are unknown and will be made available at a later date.
Intention to publish date
Participant level data
Not expected to be available
Basic results (scientific)
See additional file (ISRCTN11740813_BasicResults_24Aug18)