Insufficient sleep is associated with changes in glucose tolerance, insulin secretion, and insulin action. Despite widespread use of weight-loss diets for metabolic risk reduction, the effects of insufficient sleep on glucose regulation in overweight dieters are not known. To examine the consequences of recurrent sleep restriction on 24-h blood glucose control during diet-induced weight loss, 10 overweight and obese adults (3F/7M; mean (s.d.) age 41 (5) years; BMI 27.4 (2.0) kg/m(2)) completed two 14-day treatments with hypocaloric diet and 8.5- or 5.5-h nighttime sleep opportunity in random order 7 (3) months apart. Oral and intravenous glucose tolerance test (IVGTT) data, fasting lipids and free fatty acids (FFA), 24-h blood glucose, insulin, C-peptide, and counter-regulatory hormone measurements were collected after each treatment. Participants had comparable weight loss (1.0 (0.3) BMI units) during each treatment. Bedtime restriction reduced sleep by 131 (30) min/day. Recurrent sleep curtailment decreased 24-h serum insulin concentrations (i.e., enhanced 24-h insulin economy) without changes in oral glucose tolerance and 24-h glucose control. This was accompanied by a decline in fasting blood glucose, increased fasting FFA, which suppressed normally following glucose ingestion, and lower total and low-density lipoprotein cholesterol concentrations. Sleep-loss-related changes in counter-regulatory hormone secretion during the IVGTT limited the utility of the test in this study. In conclusion, sleep restriction enhanced 24-h insulin economy without compromising glucose homeostasis in overweight individuals placed on a balanced hypocaloric diet. The changes in fasting blood glucose, insulin, lipid and FFA concentrations in sleep-restricted dieters resembled the pattern of human metabolic adaptation to reduced carbohydrate availability.