Dietary Variety Impairs Habituation in Children

Habituation is a ubiquitous characteristic of the nervous system that has been used to understand behavioral and physiological responding for food (Epstein, Rodefer, Wisniewski, & Caggiula, 1992; Groves & Thompson, 1970; Romero & Polich, 1996). Repeated exposure to the same food stimulus leads to decreased responding (Groves & Thompson, 1970), and exposure to a novel stimulus will restore responding to the novel and the previously habituated stimulus (Epstein, Rodeter, et al., 1992; Swithers, 1995; Swithers & Martinson, 1998; Swithers-Mulvey, Miller, & Hall, 1991; Wisniewski, Epstein, & Caggiula, 1992). Slower habituation and greater recovery is associated with increased energy consumption (Wisniewski et al., 1992). Thus, exposure to a variety of foods during a meal may slow down the rate of habituation and, in turn, increase energy consumption (Epstein & Paluch, 1997; Myers Ernst & Epstein, 2002). A consistent body of research has shown that people consume more energy when given a variety of food than when given the same food (Clifton, Burton, & Sharp, 1987; Raynor & Epstein, 2001; Rolls et al., 1981; Rolls, van Duijvenvoorde, & Rolls, 1984) even when the source of the variety is small, such as different shaped pasta or different flavors of yogurt (Rolls & McDermott, 1991; Rolls, Rowe, & Rolls, 1982). This propensity to ingest a variety of foods is an evolutionarily advantageous phenomenon that may ensure a balanced nutrient intake (Raynor & Epstein, 2001). However, in the current obesiogenic environment, dietary variety may be contributing to the growing obesity epidemic (McCrory et al., 1999; Raynor & Epstein, 2001; Raynor, Jeffery, Tate, & Wing, 2004). Consumption of a variety of high energy density (HED) foods coupled with low intake of fruits and vegetables and a lack of physical activity leads to maintenance of positive energy balance and, eventually, obesity (McCrory et al., 1999; Raynor & Epstein, 2001). McCrory and colleagues (1999) reported that there was a positive relationship between body mass index (BMI) and variety of sweets, snacks, carbohydrates, entrees, and condiments consumed, and a negative relationship between BMI and consumption of a variety of vegetables (excluding potatoes) in weight-stable adults who accurately reported food intake for 6 months. Likewise, those who lost the most weight and maintained the greatest degree of weight loss in an obesity treatment program consumed the smallest variety of high fat foods, oils, and sweets and the largest variety of low fat breads and vegetables (Raynor et al., 2004). Another potential contributor to the current obesogenic environment is energy density (ED), or the amount of energy per gram of food. In studies in which ED has been manipulated, consumption of HED foods increases energy intake and consumption of low energy density (LED) foods decreases energy intake, independent of macronutrient composition of meals and subjective hunger and fullness (Ello-Martin, Ledikwe, & Rolls, 2005). These effects not only occur in single meals, but persist for subsequent meals (Bell et al., 1998; Rolls, Roe, & Meengs, 2004). Because individuals, on average, consume a consistent weight of food and subsequently report equivalent levels of fullness, despite differences in ED, it may be possible to decrease total energy intake by increasing consumption of LED foods (Bell et al., 1998; Bell & Rolls, 2001).). For example, Rolls and colleagues (2004) had participants consume “satisfying” portions of an LED food as a first course to an ad libitum pasta meal, which reduced total energy intake and energy intake of the main course when compared to a group that had no first course, despite the fact that self-reported hunger and fullness were equivalent among the groups. These studies suggest that a useful strategy to decrease energy intake among overweight individuals may be to encourage consumption of large portions of LED foods in an effort to reduce consumption of HED foods, and thus decrease total energy intake. Epidemiological research also shows that energy density may influence body weight. Participants with the highest level of fruit and vegetable consumption, had the lowest ED intakes and were the least likely to be obese (Ledikwe et al., 2006). However, other investigators question how much ED contributes to obesity (Gatenby, Aaron, Morton, & Mela, 1995; Heini & Weinsier, 1997). The food industry has been working to develop lower ED versions of highly liked foods that are equally palatable. Despite their commercial success, the increased availability and consumption of low fat (and thus lower ED) snack foods has not led to any significant reductions in average body weight (Stubbs, Ferres, & Horgan, 2000). In fact, within the United States, widespread reductions in dietary fat intake have corresponded to large increases in the incidence of obesity (Willett, 2002). Thus, changing ED in the diet by reducing the ED of high fat foods may not alter energy intake. Reduction in dietary fat is not the only way to reduce ED. Increased consumption of fruits and vegetables may be a healthier, more satisfying way to reduce overall energy intake (Rolls et al., 2004). It is, therefore, important to determine ways in which to increase fruit and vegetable consumption. The purpose of the present experiments was to investigate the impact of dietary variety and ED on habituation to food in children. In Experiment 1, we examined habituation of salivary responses to olfactory cues from the same or a variety of HED foods. In Experiment 2, we repeated this study testing habituation of motivated responding for food. In addition, because the variety effect depends on changes in the sensory characteristics of the foods, it should be independent of ED and, therefore, a variety of LED or HED foods should both decrease the rate of habituation and increase energy intake. To test this hypothesis, we measured motivated responding for the same or a variety of HED and LED foods. These experiments provide insight into factors that regulate food intake and extend our knowledge of the influence of dietary variety and ED on ingestive behavior to children.