The effect of energy density (ED) on energy intake (EI) has been assessed in short-term and long-term experiments. In the short term, it was found that ED affects EI directly in situations when the subjects cannot estimate the ED of the food; then subjects mainly monitor the weight of the food ingested. In the long term, the effects of ED on EI are modulated. Average daily EI appears to be related to ED of the food and drinks when ED is determined by specific macronutrients, but not when ED is only determined by the weight of water. Thus, the short-term effect ED has on EI cannot be extrapolated to the long term, because a possible dominating effect of the weight of water determining ED undoes the relationship of ED with EI. Moreover, in the long-term portion sizes are used to compensate for correctly estimated ED, resulting in less variation in EI than ED alone would imply. Finally, dietary restraint compensates for the effect of a relatively high ED on daily EI, whereas dietary unrestraint compensates for the effect of relatively low ED on daily EI. We conclude that the short-term effect of ED on EI is modulated by the effect of water on ED, and compensated for by the effect of dietary restraint and adapted portion sizes.