Fermentable dietary fiber has been shown to cause fat loss and to increase peptide-YY (PYY) and glucagon-like peptide 1 (GLP-1) levels in rodents. In single meal tests, humans have an increase in PYY and GLP-1 to dietary fiber, but the response of these hormones to longer-term treatment is not known. Viscofiber (Cevena Bioproducts Inc., Edmonton, AB, Canada) is a high-viscosity fermentable dietary fiber made by a proprietary process from oats and barley. Seven healthy overweight and obese subjects were treated with a calorie-restricted diet, a lifestyle change program, and 4 g of Viscofiber/day for 16 weeks. Hunger, satiety, PYY, and GLP-1 were measured before and 1 hour after a standard meal test before and at week 14 of the study. Hunger and satiety were measured by Visual Analog Scales. PYY and GLP-1 were measured by radioimmunoassay and enzyme-linked immunosorbent assay, respectively. Weight was reduced 3.07 +/- 3.13 kg (P<.05) over the 16 weeks. Fasting PYY increased 8.67 +/- 6.62 pg/mL (P<.05) and fasting GLP-1 increased 2.67 +/- 0.84 pmol/L (P<.01) at 14 weeks compared to baseline. Satiety increased 1.78 +/- 1.43 cm (P<.01) at the 1-hour post-meal time point on week 14 compared to the study baseline. We conclude that 14 weeks of treatment with Viscofiber at 4 g/day along with a lifestyle change program and diet causes weight loss and increases fasting PYY, fasting GLP-1, and satiety at 1 hour following a standard meal, which extends the single meal test observations in humans.