Objective: To examine if intake of soft drinks is more closely associated with weight gain than other energy sources and if these associations are mediated through differences in energy intake or insulin level. Methods: Data derived from the Danish part of the European Youth Heart Study (n = 359). Height, weight, and waist circumference (WC) were measured in 1997-1998 and again in 2003-2004. Results: Intake of liquid sucrose was associated with changes in waist circumference (ΔWC) (β = 0.226, p = 0.07, R2 = 0.17) as well as BMI z-scores (ΔBMIz) (β = 0.031, p = 0.05, R2 = 0.30). Associations attenuated slightly after adjusting for energy intake, but were substantially reduced when adjusting for insulin. Adjustment for both insulin and energy intake attenuated the effect of soft drinks intake on ΔBMIz, but not on ΔWC. Conclusion: Liquid sucrose seemed more clearly associated with ΔWC and ΔBMIz than other energy sources. For ΔWC, the association seemed to be based on decreases in insulin sensitivity rather than increases in energy intake, whereas for ΔBMIz the association seemed to be based on both increases in energy intake and decreases in insulin sensitivity.