Condition category
Nutritional, Metabolic, Endocrine
Date applied
Date assigned
Last edited
Retrospectively registered
Overall trial status
Recruitment status
No longer recruiting
Publication status

Plain English Summary

Background and study aims
Low vegetable consumption is a considerable health problem worldwide. A diet low in vegetables is associated with an increased risk of becoming overweight or obese, and other health related chronic diseases. Supermarkets have a major influence on daily food intake, because most foods are purchased in supermarkets. Therefore, supermarkets can be a suitable setting for health interventions to stimulate vegetable purchases. Nudging is an effective strategy to stimulate vegetable purchases. Nudging is simply defined as changes in the environment to alter people’s behavior in a predictable way, without forbidding any options. In this study we investigated the effectiveness of two nudging strategies in supermarket trolleys to stimulate vegetable purchases among supermarket customers.

Who can participate?
Supermarket customers with a shopping trolley and a cash receipt can participate in this study.

What does the study involve?
The intervention in this study consists of a green inlay in shopping trolleys with social norm messages about vegetable purchases of other customers of the supermarket. This will cover the bottom half of each trolley, indicating a place to put vegetables. The intervention days of the study are the days on which the green inlay will be used in the shopping trolleys, and the control days will be the days where there are no inlays (regular shopping trolleys). Cash receipts will be collected and surveys will be conducted among customers after they have paid for their groceries.

What are the possible benefits and risks of participating?
There are no known benefits or risks to participants taking part in this study.

Where is the study run from?
Vrije Universiteit Amsterdam (The Netherlands)

When is the study starting and how long is it expected to run for?
January 2017 to June 2018

Who is funding the study?
Vrije Universiteit Amsterdam (The Netherlands)

Who is the main contact?
Marlijn Huitink

Trial website

Contact information



Primary contact

Mrs Marlijn Huitink


Contact details

De Boelelaan 1085
1081 HV
New Zealand

Additional identifiers

EudraCT number number

Protocol/serial number


Study information

Scientific title

Social norm nudges in shopping trolleys to promote vegetable purchases: a supermarket experiment in a deprived urban area in the Netherlands


Study hypothesis

We investigated the effectiveness of two nudging strategies in shopping trolleys on the amount of vegetables purchased in a Dutch supermarket in a disadvantaged urban area. The nudges are as follows:
1. A place for vegetables
2. Social norm communication

Ethics approval

The study was conducted according to the ethical standards declared in the Helsinki declaration of 1975, as revised in 2000. Active verbal informed consent was given by all customers. The Medical Ethics Committee of the Vrije Universiteit Amsterdam confirmed that this study does not apply to the Medical Research Involving Human Subjects Act (WMO), due to the nature of the measurements (sales data and anonymous questionnaires distributed among adults). Therefore, approval was waived.

Study design

Interventional non-randomised study

Primary study design


Secondary study design

Non randomised study

Trial setting


Trial type


Patient information sheet

No participant information sheet available


Vegetable sales


The intervention consisted of three green inlays, indicating the space where customers can place their vegetables, each with a different social norm message about vegetable purchases of other customers from the participating supermarket. Customers on the intervention days received a shopping trolley with a green inlay with one of the three different social norm messages. The intervention was tested during two days (Friday evening and Saturday morning). The control days used the usual shopping trolleys with no green inlay. Cash receipts were collected and surveys conducted among customers after they had paid for their groceries.

Intervention type



Drug names

Primary outcome measure

Vegetables purchased (in grams and in items), assessed at the end of each study day over the two-week study period using:
1. Examination of cash receipts
2. Surveys with customers after they had paid for their groceries

Secondary outcome measures

The following were assessed using oral surveys in the supermarket after customers had paid for their groceries over the two-week study period:
1. Customer characteristics:
1.1. Sex
1.2. Age category
1.3. Highest obtained education
2. Customer grocery behaviour characteristics:
2.1. Number of persons and days for which groceries were purchases
2.2. Use of a shopping list or not
2.3. Place customers purchased vegetables most often
2.4. If customers thought that they purchased less, more or the same amount of vegetables during this shopping trip as they usually would

Overall trial start date


Overall trial end date


Reason abandoned (if study stopped)


Participant inclusion criteria

Supermarket customers in Amsterdam with a shopping trolley and a cash receipt

Participant type


Age group




Target number of participants


Total final enrolment


Participant exclusion criteria

1. Not willing to consent to having photograph of cash receipt taken
2. Purchased groceries for more than 12 persons for one day

Recruitment start date


Recruitment end date



Countries of recruitment


Trial participating centre

Vrije Universiteit Amsterdam
De Boelelaan 1085
1081 HV

Sponsor information


Vrije Universiteit Amsterdam

Sponsor details

De Boelelaan 1085
1081 HV

Sponsor type




Funder type

Not defined

Funder name

Vrije Universiteit Amsterdam

Alternative name(s)

Funding Body Type

Funding Body Subtype


Results and Publications

Publication and dissemination plan

Publication of a research article with submission planned in 2018

IPD sharing statement:
The 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)

Publication list

2020 results in (added 27/07/2020)

Publication citations

Additional files

Editorial Notes

27/07/2020: The following changes have been made: 1. Publication reference added. 2. The final enrolment number has been added from the reference.