We conducted a double-blind, placebo-controlled, within-subject crossover study to investigate the effect of covert substitution of Olestra, a non-caloric fat-substitute, for conventional fat on self-selected macronutrient and energy intake in lean and obese men and women. 53 subjects (BMI = 19-36; age=22-61) were studied during two 14-day treatment periods (with a 7-day washout between feeding periods). All foods consumed by subjects were provided by the site except during washout. Breakfast and dinner were consumed at the study site and carry out lunch and snack items were consumed elsewhere. Subjects were required to consume core foods providing 20-35 g of Olestra (approximately a 10% dilution of estimated energy requirements), or the same foods containing placebo triglycéride. Additional items could be selected from foods that varied in macronutrient composition. Total energy was 8% lower and fat intake was 11% lower during the Olestra treatment phase compared to the placebo phase (p< 0.0001). This resulted in subjects consuming 32% of total energy from fat during the placebo period and 27% of total energy from fat during Olestra treatment. Neither carbohydrate nor protein intake differed between conditions. Olestra appears to facilitate a reduction in dietary fat intake as well as a reduction in total energy intake.