Background:Results of prior studies of the effect of viscosity reduction of high-energy-density, starch-containing diets on young children's energy intakes are inconsistent, possibly because of differences in the characteristics of the unmodified diets with which the low-viscosity diets were compared. Objective: Our objective was to determine the effects of dietary viscosity and energy density on total daily energy consumption by young, non-breast-fed children. Design: We measured the amount of food consumed and the duration of meals during 3 substudies, in each of which 3 study diets were offered for 4 consecutive days each in random sequence: high energy density, high viscosity (HD-HV); high energy density, low viscosity (HD-LV); and low energy density, low viscosity (LD-LV). The viscosity and energy density of the unmodified starchcontaining HD-HV diet were varied across substudies to determine whether the effect of amylase liquefaction was related to the initial characteristics of the HD-HV diet. The viscosity of the HV diets ranged from 79 000 to 568 000 mPa · s; energy density of the HD diets ranged from Ϸ4.18 to 4.93 kJ (1.00-1.18 kcal)/g. Viscosity of the LV diets was Ϸ3000 mPa · s and the energy density of the LD diets was Ϸ2.47 kJ (0.6 kcal)/g. Results:In each substudy, children consumed more of the LD-LV diet (g · kg body wt Ϫ1 · d Ϫ1 ) than of the other diets and more of the HD-LV diet than of the HD-HV diet (P < 0.001). Energy consumption from the HD-LV diet was greater than from the other diets (P < 0.001), but the energy intakes from the latter diets were not significantly different. Conclusion: Amylase liquefaction of HD-HV porridges resulted in increased energy consumption by young children.Am J Clin Nutr 1999;70:285-91.