Objectives:To investigate whether dietary glycaemic index (GI) and glycaemic load (GL) were associated with subsequent weight and waist circumference change.Design:Population-based prospective cohort study.Setting:Five European countries, which are Denmark, Germany, Italy, The Netherlands and the United Kingdom.Participants:A total of 89 432 participants, aged 20-78 years (mean =53 years) at baseline and followed for 1.9-12.5 years (mean=6.5 years). All participants were free of self-reported cancer, cardiovascular diseases and diabetes at baseline.Methods:Glycaemic index and GL were calculated on the basis of dietary intake assessed by food frequency questionnaires and by using a GI table developed for this study with published GI values as the main sources. Anthropometric data were collected both at baseline and at the end of follow-up. Multiple linear regression analyses were conducted in each centre and random-effect meta-analyses were used to combine the effects. Adjustment was made for baseline anthropometrics, demographic and lifestyle factors, follow-up duration and other dietary factors.Results:Mean GI and GL were 57 and 134, respectively. Associations of GI and GL with subsequent changes of weight and waist circumference were heterogeneous across centres. Overall, with every 10-unit higher in GI, weight increased by 34 g per year (95% confidence interval (CI): -47, 115) and waist circumference increased by 0.19 cm per year (95% CI: 0.11, 0.27). With every 50-unit higher in GL, weight increased by 10 g per year (95% CI: -65, 85) and waist circumference increased by 0.06 cm per year (95% CI: -0.01, 0.13).Conclusions:Our findings do not support an effect of GI or GL on weight change. The positively significant association between GI, not GL, and subsequent gain in waist circumference may imply a beneficial role of lower GI diets in the prevention of abdominal obesity. However, further studies are needed to confirm this finding given the small effect observed in this study.International Journal of Obesity advance online publication, 25 August 2009; doi:10.1038/ijo.2009.163.