Epidemiological evidence shows an inverse relationship between dietary fibre intake and body weight gain. Oat β-glucan, a soluble fibre alters appetite hormones and subjective satiety in acute meal test studies, but its effects have not been demonstrated with chronic consumption. The present study aimed to test the effects in women of two different doses of oat β-glucan on weight loss and hormones associated with appetite regulation. In a 3-month parallel trial, sixty-six overweight females were randomised into one of three 2 MJ energy-deficit diets: a control and two interventions including 5–6 g or 8–9 g β-glucan. Anthropometric and metabolic variables (blood glucose level, insulin, total cholesterol (TC), LDL, HDL, TAG and leptin), together with markers of appetite regulation (cholecystokinin (CCK), glucagon-like peptide-1 (GLP-1), ghrelin, peptide YY (PYY) and PYY3-36) were measured at baseline and at 3 months. After 3 months, all groups lost weight (P < 0·001) and showed a reduced waist circumference (P < 0·001). The study sample also showed reductions in TC, LDL, HDL, leptin, PYY, GLP-1 values (all P < 0·001) and an increase in CCK levels (P < 0·001). No significant differences were noted between the groups for all outcome values except PYY levels (P = 0·018). In broad terms, the addition of oat β-glucan did not enhance the effect of energy restriction on weight loss in mildly overweight women, although wide variations in observed results suggests that individual responsiveness may be an issue.