of intake in an extensive review of the literature on human food intake (Spitzer and Rodin, 1981), it is possible that other characteristics of foods such as the energy density or nutrient composition could have an impact on energy intake.

Various types of foods satisfy hunger differently (Kissileff, 1984; Rolls et al., 1990). The reasons for these differences in satiating effects are not clear. Among the causative factors that have been suggested are rate of consumption of a food, the sensory properties of the food, and beliefs about the satiety value of a food (Kissileff, 1984)/

Soup is an example of a food that is highly satiating. In a clinical survey in which intakes were analyzed from food diaries, Jordan et al. (1981) found that meals that included soup were associated both with lower caloric intakes within the meals and with lower daily caloric intakes than those meals without soup. Several studies have confirmed that soup is a highly satiating food (Kissileff et al., 1984; Rolls et al., 1990). At least part of the explanation is the low energy density of soup. Energy density, that is the calories in a given weight of food, could affect satiety by influencing the rate at which nutrients reach receptors involved in satiety (Kissileff, 1985). Foods with a low energy density require that a greater bulk of food be consumed for a given level of energy intake. The bulk of food to be consumed affects eating rate, gastric distension, and intestinal stimulation. Also, it is likely that individuals have learned the appropriate portion sizes that they should eat to experience satiety.

Energy density of foods can affect daily energy intake and body weight. In one study (Duncan et al., 1983), obese and normal-weight subjects had access to one of two different diets, for 5 days each. One diet had twice the energy density of the other; the low-energy-density diet was low in fats and sugars and high in fiber. The subjects consumed three meals a day and were allowed to eat as much of the available foods as they liked at each meal. Subjects on the high-energy-density diet. consumed nearly twice as many calories as those on the low-energy-density diet. Subjects on the low-energy-density diet were slightly hungrier at mealtimes but found the meals to be satiating. The diets in this study differed not only in energy density, but also in the fat content and in the amount of fiber, both of which could affect the amount of food consumed.

Foods high in fat can be readily overeaten, not only because fat increases the energy density of foods, but also because it contributes to the palatability of foods (Drewnowski, 1988). A key question is whether fat and carbohydrate,