Understandably, there is a very strong focus in obesity
research on the diets of schoolchildren with many schools now attempting to
implement healthy eating policies.
Equally, there has been considerable concern about the existence of food
retail outlets nearby to schools to which the schoolchildren have access. A
group at the University of Oxford has recently published a meta-analysis of all
relevant studies, which set out to examine the relationship between obesity
outcomes and the proximity of food retail outlets to schools[1].
The authors completed a search of 10 on-line library
databases and identified several thousand studies but, as ever, in
meta-analyses, many of the initial studies were rejected for a variety of
reasons leaving the authors with 30 full studies which met all of the a priori inclusion criteria. Each study had
to have defined exactly what was meant by the retail food environment and to
have measure quantitatively the relationship between food purchase patterns and
obesity-related outcomes. Most of the papers were published between 2011 and
2013 and most were cross-sectional with children ranging in age from five to
seventeen years. More than three quarters had sample sizes of over 1,000.
Of the 30 studies, the majority used a defined “buffer zone”
around the school but some used route maps between the pupil’s home and school.
GIS (Geographic Information Systems) software was the main source of
information on retail outlets either within the designated buffer zone or
school route. In general the buffer zone applied a distance of between 0.1 to
3.0 miles while the route approach generally used distances of 50 to 100 meters
from the road travelled to and from school. The main outcome studied was the
child’s BMI (kg/m2). The second most frequent measure of outcome was
food intake but this appeared generally to be related to a narrow range of
foods: fruit and vegetables, soda drinks or fast food. Some of course used
several measures and just three used the overall diet quality index of the schoolchildren
which would have included all sources of foods at all times of the day.
One study focused on fast food purchases and found a
statistically significant positive association between fast food purchasing and
the density of fast food outlets. Ten
studies examined the relationship between food outlets in general and the consumption of sugar sweetened
beverages and of fast food, including crisps, sweets, biscuits, fried food,
sugar sweetened beverages and fast foods. Within these 10 papers, a total of 54
associations were examined and only two of these showed a statistically
significant association. Four papers examined the association between fruit and
vegetable consumption and food retail outlets and within these a total of 32 associations
were examined. Only three showed statistically significant associations. Within
the 30 studies, only three had data on the overall quality of the pupil’s diet
and food retail outlet density. Two of these showed a significant association
between diet quality of food outlets. In one case, the data showed a
significantly higher diet quality index among pupils attending a school where
the nearest retail outlet was greater than 1 km away as compared to those where
the distance was less than 1km away. The second study found that the greater
the distance to the nearest grocers the better was the overall diet of the
pupils.
This is an important paper for several reasons. Firstly, it
is a very well conducted study published in a high impact journal. Secondly, it
highlights how the existence of evidence is happily ignored by those policy
makers who want to place restrictions on the availability of food outlets
within the vicinity of schools. Thirdly, it shows that the outcome variables
which are easy to measure such as fruit and vegetable intake, soda intake or
BMI yield fairly useless conclusions since they do not relate the one aspect of
the determinants of food choice (school associated food outlets) to the
totality of the effects of all food choice in terms of overall daily nutritional
quality. Once again, we see a majority of studies in what is a very important
area of public health nutrition, bedevilled by bad design. In the three studies,
which did look at the overall quality of the pupil’s diet and density of food
retail outlets two showed some significant associations. Now do two swallows
make a summer?. No, but they point the way forward for the conduct of scientifically
rigorous studies in this very important area of public health nutrition. To
discover that the proximity of food outlets influenced specific food intake is
of zero importance in public health nutrition. We need to know the full
accurate daily nutrient intakes and only then can we judge whether any aspect
of the obesigenic environment id truly influencing overall nutritional quality.
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