Supermarket interventions have been a commonly used treatment for problems of fresh fruit accessibility in areas of previously limited availability, their wide ranges of healthy products and lower-prices making them seemingly perfect for promoting better diets. Empirical studies likewise fall in favour. However, this diversity also serves to give consumers opportunity to entrench bad habits and simply purchase more of the unhealthy foods they enjoy. In this paper we develop a new health index based upon UK government guidelines and look to the Seacroft Intervention Study for empirical evidence of supermarket impact thereupon. Using fixed effects unconditional quantile regression to provide robustness to our parameter estimates against covariate specification, we reinforce the message that supermarkets are not a panacea for dietary improvement. Whilst diversity increases post-intervention it is unlikely to be healthful, entrenching poor dietary habits rather than delivering improvement as intended. Careful consideration of planning policy, health education and sector regulation is needed.