This study was designed to test whether a high fiber preload can suppress food intake at a subsequent test meal. Fifty male undergraduates, 31 of normal body weight and 19 at least 15 per cent overweight, participated as paid volunteers. So as not to inhibit spontaneous food intake, they were told that the investigators were studying the effects of the parasympathetic nervous system on cognitive processes and they were given a picture rating task to perform. The stated rationale for having the subjects eat the preload between two sets of pictures was to alter the state of parasympathetic activation. The preload consisted of two roast beef sandwich halves containing a total of 400 kcal and either 5.2 or 0.2 g of crude fiber in the bread. The preload was eaten by the subjects, their meal was intentionally interrupted and then they were allowed to finish eating 30-45 minutes later (test meal). Obese subjects ate significantly fewer sandwich halves after the high than after the low fiber preload. Obese subjects ate significantly more than non-obese subjects in the low fiber treatment so that the effect of the high fiber was to normalize their intake. Although both obese and normal-weight subjects reported feeling fuller after the high fiber preload, the non-obese subjects ate virtually the same amount in both treatments. Obese subjects reported liking the high fiber bread less well than the low fiber bread but additional statistical analyses showed an intake-suppressing effect of fiber even after controlling for bread rating. These results support the hypothesis that fiber reduces caloric intake in obese people.