A randomised, controlled supermarket intervention trial

Rationale

Unhealthy diet plays a role in 11,000 deaths every year in New Zealand and healthier diets are important in preventing common diseases including heart disease, stroke, cancer, and diabetes.  Most of our food is bought at supermarkets, so choosing healthier supermarket foods is likely to have important health benefits. The previous SHOP pilot study demonstrated the feasibility of conducting a large randomised trial of strategies to improve supermarket food purchases.

Aims

The primary aim was to assess the effect of price discounts and tailored nutrition education on the saturated fat content of supermarket food purchases. Secondary aims included evaluation of the effect of the interventions on other macronutrient contents of purchased supermarket food, namely: energy density, total fat, carbohydrate, protein, sugar, sodium, and fibre. Data on the effect of the interventions on purchase of specific food items (e.g. fruit and vegetables) and healthier options will also be collected.

Design

The aim was to recruit 1,200 primary household shoppers who shopped regularly at one of eight participating supermarket stores in the Wellington region. Participants were randomised to one of four intervention arms: (1) culturally targeted tailored nutrition education; (2) price discounts on healthier food purchases; (3) a combination of discounts and nutrition education; or (4) a control group. Baseline shopping data were collected for three months. Intervention lasted six months, and the main study outcomes were measured at that time. Follow-up continued for another six months to determine any sustained impact of the interventions. Electronic data on food purchases were collected over the full 15-month period of the trial using barcode scanners operated by the primary household shoppers.

Update

The SHOP trial was successfully completed in February 2009.  1,104 (248 Maori, 101 Pacific, and 755 non-Maori non-Pacific) supermarket shoppers took part.  Data lock occurred in March 2009 and analyses have now been completed.  The SHOP trial results (including some background and methodology) were presented at the International Society for Behavioural Nutrition and Physical Activity conference in Lisbon, Portugal, June, 2009, and were published in the American Journal of Clinical Nutrition in March 2010.

Funding

This study is funded by the Health Research Council of New Zealand (# 06/379)
Helen Eyles is supported by a National Heart Foundation post-graduate scholarship (# 1285)

CTRU Contact

Cliona Ni Mhurchu, Principal Investigator

The study was designed in collaboration with the Wellington School of Medicine. CTRU and Wellington School of Medicine were involved in the overall co-ordination of the project. Study management, data management and statistical analyses were undertaken by the CTRU.

Collaborators

Tony Blakely and Sarah McKenzie, Wellington School of Medicine and Health Sciences, University of Otago
Paul Brown, Health Systems, University of Auckland
Mafi-Funaki-Tahifote and Iutita Rusk, Pacific Islands Heartbeat Programme
Leonie Matoe, Te Hotu Manawa Maori

Publications

Main Results Paper:
Ni Mhurchu C, Blakely T, Jiang Y, Eyles HC, Rodgers A. Effects of price discounts and tailored nutrition education on supermarket purchases: a randomized controlled trial. American Journal of Clinical Nutrition 2010;91:736-747.

1. Blakely T, Ni Mhurchu C, Jiang Y, Matoe L, Funaki-Tahifote M, Helen C Eyles, Rachel H Foster, McKenzie S, Rodgers A. Do effects of price discounts and nutrition education on food purchases vary by ethnicity, income and education? Results from a randomised, controlled trial. Journal of Epidemiology and Community Health 2011. doi: 10.1136/jech.2010.118588.
2. Eyles H, Jiang Y, Ni Mhurchu C. Use of household supermarket sales data to estimate nutrient intakes: a comparison with repeat 24-hour dietary recalls. Journal of the American Dietetic Association 2010;110:106-110.
3. Eyles H, Rodgers A, Ni Mhurchu C. Use of electronic sales data to tailor nutrition education resources for an ethnically diverse population. Journal of Human Nutrition and Dietetics 2010;23(1):38-47.
4. Eyles H, Gorton D, Ni Mhurchu C. Classification of ‘healthier’ and ‘less healthy’ supermarket foods by two Australasian nutrient profiling models.  New Zealand Medical Journal 2010; 123(1322): 8-20  http://www.nzma.org.nz/journal/123-1322/4338/
5. Ni Mhurchu C, Blakely T, Jiang Y, Eyles HC, Rodgers A. Effects of price discounts and tailored nutrition education on supermarket purchases: a randomized controlled trial. American Journal of Clinical Nutrition 2010;91:736-747.  [Main results paper]
6. Eyles H, Ni Mhurchu C, Wharemate l, Funaki-Tahifote M, Lanumata T, Rodgers A. Developing nutrition education resources for a multi-ethnic population in New Zealand. Health Education Research 2009; 24(4):558-574. doi:10.1093/her/cyn057.
7. Eyles H, Ni Mhurchu C.  Does tailoring make a difference?  A systematic review of the long-term effectiveness of tailored nutrition education for adults.  Nutrition Reviews 2009; 67 (8): 464-480. doi:10.1111/j.1753-4887.2009.00219.x
8. Ni Mhurchu C, Blakely T, Funaki-Tahifote M, McKerchar C, Wilton J, Chua S, Jiang Y. Inclusion of indigenous and ethnic minority populations in intervention trials: challenges and strategies in a New Zealand supermarket study. Journal of Epidemiology and Community Health 2009;63:850-855. doi:10.1136/jech.2008.081109.
9. Kruse K, Blakely T, Eyles H.C.  Lessons learned from co-ordinating a group health education workshop for Pacific people [letter]. Health Promotion Journal of Australia 2008; 19(3): 232-232.