Yes / Supermarkets, with vast product ranges and relatively low prices, are an established solution to problems of availability of healthy foodstuffs in areas of limited retail access. However, where they may indeed raise consumption of desirable goods they also open up new opportunities to buy less healthful items for less, a situation which potentially undermines their ability to improve diet. Using under-reported diary data from the Seacroft Intervention Study in the United Kingdom takes this paper beyond the extant fruit and vegetable focus, giving it scope to explore the full effect of supermarkets. Quantile regressions show existing behaviours are reinforced, and intervention stores may do little to improve diet. Switching to Tesco Seacroft is shown to increase the portions of unhealthy food consumed by almost 1 portion per day for the least healthy. Managing demand through promoting balanced diets and restricting offers on unhealthy items will be more effective than intervention, and is an essential accompaniment to new large format retailers if they are not to entrench dietary inequality further. Policymakers and practitioners alike should avoided being distracted by aggregate conclusions if food deserts are to be truly tackled.