Can a planning exercise help people eat the less meat they intend to?
A short mental contrasting and if-then planning exercise made people's intention to cut meat actually predict how much they cut, which information alone did not.
Source
Supporting Sustainable Food Consumption: Mental Contrasting with Implementation Intentions (MCII) Aligns Intentions and Behavior
Study at a glance
- Design
- RCT — Randomised two-arm experiment: information text only vs information plus MCII, with 7-day meat diaries at baseline, 1 week and about 4 weeks after the intervention.
- N
- N=55 · 60 non-vegetarian university members randomised; 55 completed the study and were analysed.
- Population
- Mostly student non-vegetarian members of a German university
- Outcome
- Reduction in diary-recorded daily meat consumption (g/day) and how strongly baseline intention predicted that reduction
Structured fields used in claim comparison tables when every cited study has a complete layer.
What they did
60 non-vegetarian university members kept a week-long meat diary, then rated how strongly they intended to eat less meat. All read an information text about the environmental, health, ethical and social reasons to eat less meat; half were randomly assigned to also do MCII, writing a meat goal, its best outcome, their main obstacles and four if-then plans. They then kept meat diaries in the week after the session and again in week 5.
What they found
Both groups cut their meat intake, and the MCII group cut somewhat more by week 5 (d = 0.61). Crucially, in the MCII group intention correlated with reduction (r about 0.53-0.54), whereas in the information-only group it did not. MCII added a benefit only for people with at least moderate intentions (above roughly 4.60 on the 1-7 intention scale in the first week after the session); perceived experimenter demand did not differ between groups.
The limits
What it doesn't show
The sample was small and mostly students, who already ate about half the average German amount of meat, so results may not generalise. There was no no-intervention control group, so it is unclear how much of the overall drop came from the information text, keeping a diary (self-monitoring), or time. Meat intake was self-reported in weight categories and the follow-up lasted only about a month; in a baseline-matched reanalysis the week-5 interaction was no longer significant.
Key terms
- Intention-behaviour gap
- The frequent mismatch between what people intend to do and what they actually do.
- Implementation intention
- An if-then plan linking a specific situation to a specific action, e.g. 'If X happens, then I will do Y'.
- Mental contrasting
- Imagining a desired future outcome and then the main obstacle in present reality that stands in the way.
- Moderation
- When the strength of a relationship between two variables depends on a third variable, here intervention condition.
- Johnson-Neyman technique
- A method for finding the value of a moderator at which an effect becomes statistically significant.
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Quiz yourself
What did the control group receive?
Common questions
Did the MCII group simply eat less meat than the control group?
They reduced more by week 5, but because they started slightly higher, their absolute intake at follow-up was not lower. The key finding is that their reduction matched their intentions.
Why did the information-only group also reduce meat?
The authors suspect that keeping detailed meat diaries acted as self-monitoring, a known behaviour-change technique, in addition to the information text.
Does MCII help people who barely want to change?
No. The extra benefit appeared only for people with moderate to strong intentions to reduce meat.
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