Olestra is a fat substitute made from fatty acids esterified to sucrose and can be used in the preparation of virtually any food made with fat. Foods made with olestra retain the mouthfeel, palatability and satiating effects of their full-fat counterparts without providing any digestible energy. Because olestra provides no energy, it has the potential to be a useful tool in weight loss and weight maintenance. Short-term studies of olestra replacement in foods demonstrate that fat replacement leads to a net reduction in fat intake. When excess total energy is available, fat replacement also reduces total energy intake in lean and obese men and women. In longer-term studies in which olestra is incorporated into the daily diet, there is an incomplete compensation for the fat energy replaced by olestra. When overweight men consumed olestra as part of a varied diet over nine months, weight loss continued for the duration of the study, whereas individuals receiving a typical low-fat diet regained most of the initial weight lost. Other studies are underway to examine the usefulness of olestra in long-term weight maintenance following weight loss. Post-marketing surveillance of olestra foods in the United States indicates that substitution of olestra for only 1–2 g of fat d−1 may be sufficient to prevent the average weight gain reported in adults of 0.5–1.0 kg year−1.