Dietary fiber (DF) and protein are essential constituents of a healthy diet and are well known for their high satiety impact. However, little is known about their influence on postprandial gastrointestinal (GI) peptide release. Our aim in this single-blind, randomized, cross-over study was to investigate the effects of DF and/or protein enrichments on satiety-related metabolic and hormonal responses. Sixteen healthy, nonobese volunteers participated in the study and ingested 1 of 5 isoenergetic test meals in a randomized order on separate days. The test meals were as follows: 1) low in protein (2.8 g) and fiber (7.6 g); 2) low in protein (2.6 g) and high in soluble fiber (psyllium, 23.0 g); 3) high in protein (soy, 19.7 g) and low in fiber (6.2 g); 4) high in protein (18.4 g) and fiber (23.0 g); and 5) white wheat bread. Serum insulin and plasma glucose, ghrelin, glucagon-like peptide 1 (GLP-1), and peptide YY (PYY) concentrations were determined for 2 h following the meals. In addition, hunger and satiety ratings were collected. Postprandial glucose, insulin, ghrelin, GLP-1, and PYY responses all differed among the meals (P <or= 0.05). Fiber-enriched meals decreased glucose, insulin, ghrelin, and PYY responses; in addition, PYY secretion was prolonged compared with the other meals. The postprandial GLP-1 concentration was significantly suppressed after a fiber- and protein-rich meal, in contrast to the initial increases following the other meals. However, postprandial ratings of appetite were mostly similar after the test meals. In conclusion, solid meals enriched with psyllium fiber strongly modified postprandial signals arising from the GI tract.