An important question that has been raised recently is whether it is mainly the energy density (ED) of the food consumed or its macronutrient composition that determines daily energy intake (EI). In this scope, the effect of ED on EI has been assessed in short-term as well as long-term experiments. Over the short term, i.e., during a meal, it was found that ED affects EI directly; then subjects mainly monitor the weight of the food ingested. Over the long term, the effects of ED on EI are modulated. Average daily energy intake (ADEI) does not only consist of meals but also includes snacks and drinks. ADEI appears to be related to ED of the food and drinks where ED is at least determined by specific macronutrients (primarily fat and carbohydrate), but not when ED is determined only by the weight of water. With respect to the separate effects of the ED of foods and of drinks on ADEI, only ED from foods had a significant relationship with total EI. Moreover, during daily food intake, subjects seem to adapt their portion sizes to estimated EDs. Long-term studies have shown that dietary restraint compensates for the effect of increases in ED on ADEI, whereas unrestrained eaters compensate for the effect of decreases in ED on ADEI. In conclusion, ED determines short-term EI. This cannot be extrapolated to the long term because only the ED of food, and not the ED of drinks, determines total EI. In addition, over the long term, the short-term effect is modulated by dietary restraint and adapted portion sizes. ED is not a universal concept that determines EI, yet rather a characteristic of the macronutrients: mainly fat and carbohydrate contributing to variation in EI.