Should we use absolute or relative measures when assessing foodscape exposure in relation to fruit and vegetable intake? Evidence from a wide-scale Canadian study.

OBJECTIVE: This paper explores which of absolute (i.e. densities of "healthy" and "unhealthy" food outlets taken separately) or relative (i.e. the percentage of "healthy" outlets) measures of foodscape exposure better predicts fruit and vegetable intake (FVI), and whether those associations are modified by gender and city in Canada. METHODS: Self-reported FVI from participants of four cycles (2007-2010) of the repeated cross-sectional Canadian Community Health Survey living in the five largest metropolitan areas of Canada (n=49,403) was analyzed. Absolute and relative measures of foodscape exposure were computed at participants' residential postal codes. Linear regression models, both in the whole sample and in gender- and city-stratified samples, were used to explore the associations between exposure measures and FVI. RESULTS: The percentage of healthy outlets was strongly associated with FVI among men both in Toronto/Montreal (β=0.012; P<0.001), and in Calgary/Ottawa/Vancouver (β=0.008; P<0.001), but not among women. Observed associations of absolute measures with FVI were either weak or faced multicollinearity issues. Overall, models with the relative measure showed the best fit. CONCLUSIONS: Relative measures should be more widely used when assessing foodscape influences on diet. The absence of a single effect of the foodscape on diet positions sub-group analysis as a promising avenue for research.