Background: Specially manufactured low-fat and non-fat foods have become increasingly available over the past 2 decades and controversy has surrounded the issue of whether these products have beneficial or adverse effects on the health and nutritional status of Americans. Methods: This study examines the association of olestra consumption with changes in dietary intakes of energy, fat, and cholesterol and changes in weight and serum lipid concentrations. Data are from a cohort of 335 participants in the Olestra Post-Marketing Surveillance Study sentinel site in Marion County (Indianapolis, Ind). Diet, weight, and serum lipid levels were assessed before the market release of olestra and 1 year later, after olestra-containing foods were widely available. Olestra intake at the 1-year follow-up was categorized as none, low (>0 to 0.4 g/d), moderate (0.4 to 2.0 g/d), and heavy (>2.0 g/d). Results: Participants in the heavy olestra consumption category significantly reduced dietary intake of percentage of energy from fat (2.7 percentage points, P for trend, .003) and saturated fat (1.1 percentage points, P for trend, .02). Consumers in the highest category of olestra consumption had statistically significantly reduced total serum cholesterol levels of -0.54 mmol/L (-21 mg/dL) compared with -0.14 mmol/L (-5 mg/dL) among olestra nonconsumers (P for trend, .03). Conclusions: These results indicate that introduction of a new fat substitute (olestra) in the US market was associated with healthful changes in dietary fat intake and serum cholesterol concentrations among consumers who chose to consume olestra-containing foods.