The limitations of this study relate mainly to its observational nature, with the possibility of residual confounding precluding definitive conclusions about causality, and to reliance on self-reported diet and other lifestyle factors. Our conclusions are restricted to frequency of fast-food restaurant use because we were unable to analyse sufficiently the considerable range of
available fast-food items and their portion sizes. Nonetheless, our results might underestimate the true magnitude of the effect because of measurement error and thorough adjustment for many co variates that might be on the causal pathway—eg, food groups and nutrients. Furthermore, several analytical issues might have affected our results. Measurement error, if non differential,would tend to result in attenuated estimates of the strength of association between fast-food intake and the outcome variables. Similarly, analyses of changes are limited by floor and ceiling effects in that some people never eat fast food (so cannot decrease) or
eat most meals at fast-food restaurants (so cannot increase). These difficulties would also tend to attenuate noted relations compared with the true relation (such as would be observed in a clinical trial of investigator controlled increase or decrease in fast-food intake). Only
data obtained in the first and last CARDIA examination