A twin study of the effects of energy density and palatability on energy intake of individual foods

The relative effects of energy density and palatability on energy intake, and whether there are familial influences on these effects, are not known. We investigated this issue in 7 pairs of healthy, male monozygotic twins (mean ± SD age 26.3 ± 8.6 years, BMI 23.7 ± 3.2 kg/m²) in a clinical study involving covert ad libitum feeding of high-fat (HF, ∼40%) and low-fat (LF, ∼20%) diets in two 9-day phases. Diets were matched for average energy density, protein, fiber, and initial reported taste pleasantness, but these factors varied among the individual foods. Relationships between energy density, palatability, and energy intake were explored using regression and path analyses. Food energy density was positively associated with average taste pleasantness (r = 0.46, P = 0.03) independent of fat content, while energy intake from individual foods was positively associated with both energy density (r = 0.56, P = 0.007) and taste pleasantness (r = 0.73, P < 0.0001). In path analysis, both energy density and taste pleasantness directly influenced energy intake, and energy density also indirectly influenced energy intake by influencing taste pleasantness. In addition, there were significant within-twin pair similarities for the energy density-taste pleasantness and energy density-energy intake relationships (P < 0.03) with the result that some twin pairs but not others identified foods high in energy density as more pleasant tasting and consumed relatively more energy from them compared to foods low in energy density. These results suggest that there are familial influences on the extent to which high energy density foods are preferred and contribute to total energy intake.