Access to fast food has often been blamed for the rise in obesity which in turn has motivated policies to curb the spread of fast food. However, robust evidence in this area is scarce, particularly using data outside of the US. It is difficult to estimate a causal effect of fast food given spatial sorting and ever-present exposure. We investigate whether the residential access to fast food increased BMI of adolescents at a time when fast food restaurants started to open in the UK. The time period presents the study with large spatial and temporal differences in exposure as well as plausibly exogenous variation. We merge data on the location and timing of the first openings of all fast food outlets in the UK from 1968-1986, with data on objectively measured BMI from the 1970 British Cohort Survey. The relationship between adolescent BMI and the distance from the respondents' homes and time since opening, is studied using OLS and Instrumental Variables regression. We find that fast food exposure had no effect on BMI. Extensive robustness checks do not change our conclusion.