ObjectivesTo examine if obesity status and socio-economic and lifestyle factors are associated with self-reported past food habit change, and also whether the level of obesity depends on the reason for change.DesignCross-sectional analysis within the Malmo Diet and Cancer (MDC) study using data from the baseline examination and the extensive socio-economic and lifestyle questionnaire including questions of past food habit change. The risk of having changed food habits in the past was examined using logistic regression. Mean differences in obesity status across categories of reasons for past food habit change were examined using analysis of variance.SettingMalm�, the third largest city in Sweden.SubjectsA sub-sample (15 282 women and 9867 men) from the MDC cohort recruited from 1992 to 1996.ResultsIndividuals with body mass index (BMI) >30 kg m−2 had an increased risk of having reported past food habit change compared with individuals with BMI <25 kg m−2 (odds ratio (OR) = 1.63, 95% confidence interval (CI) = 1.48–1.83 for women; OR = 1.53, 95% CI = 1.32–1.76 for men). The highest level of obesity was observed among individuals who had changed their diet due to reasons related to the metabolic syndrome. Changers were more likely to be highly educated and to live alone, be retired, ex-smokers and non-drinkers at baseline.ConclusionsBecause past food habit change is related to obesity and other lifestyle and socio-economic factors, a complex confounding situation may exist that could seriously influence observed relationships between diet and disease. Studies need to collect information on past food habit change and take this information into account in the analysis and when interpreting study outcomes.