British Journal of Health Psychology

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Volume 19 Issue 1 (February 2014), Pages 1-234

Partner‐ and planning‐based interventions to reduce fat consumption: Randomized controlled trial (pages 132-148)


The research tested the efficacy of partner‐ and planning‐based interventions to reduce dietary fat intake over a 6‐month period.


Randomized controlled, blinded, parallel trial.


A computer randomization feature was used to allocate council employees (= 427, of which 393 completed baseline measures) to one of four conditions (partner + implementation intentions, partner‐only, implementation intentions, and control group) before they completed measures at baseline and follow‐ups at 1, 3, and 6 months post‐baseline. Outcome measures were comprised of validated self‐report measures of dietary fat intake (saturated fat intake, fat intake, ratio of ‘good’ fats to ‘bad’ fats); psychosocial mediators (enjoyment, intention, self‐efficacy, social influence, partner support); weight and waist size (baseline and 6 months only).


Data from 393 participants were analysed in accordance with intention‐to‐treat analyses. All intervention groups reported greater reductions in fat intake than the control group at 3 months. The partner‐based groups increased the ratio of ‘good’ fats to ‘bad’ fats at 3 and 6 months and lost more inches on their waist, versus the non‐partner groups. The impacts of the partner‐based manipulations on outcomes were partially mediated by greater perceived social influences, partner support, and enjoyment of avoiding high‐fat foods. The partner‐based interventions also increased intention and self‐efficacy. However, the effects in this study were typically small and generally marginally significant.


Partner‐based interventions had some positive benefits on dietary‐related outcomes at 3 and 6 months. Support for implementation intentions was more limited.

Statement of contribution

What is already known on this subject?

  • Minimal interventions deliverable at a population level can have significant health impact.
  • Encouraging partner support for dietary‐related changes has yielded mixed findings.
  • Implementation intentions have a small benefit on reducing the intake of unhealthy foods.

What does this study add?

  • This trial is the first test of the effect of collaborative implementation intentions on diet.
  • Benefits of partner‐based strategies on psychosocial, behavioural, and physical outcomes are found.

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