The separate effects of energy restriction and weight loss on serum lipids were studied in 24 postmenopausal moderately obese women before and after weight loss of > 10 kg to normal weight. Fasting serum triglycerides (TGs). total cholesterol (TC). high-density-lipoprotein (HDL) and low-density-lipoprotcin (LDL) cholesterol, and insulin were measured at the end of four 10-d in-hospital phases, two before and two after weight loss: phase I. stable weight: phase II. 3350 kJ/d (800 kcal/d). followed by outpatient weight loss: phase III. 3350 kJ/ d (800 kcal/d): and phase IV. stable weight. Diet composition and exercise were constant the entire study. Energy-restriction effect was determined by comparing average values in stable-weight phases (1 and IV) with low-energy phases (II and III): weight-loss effect was determined by comparing values in obese phases (I and II) with reduced-weight phases (III and IV). Energy restriction lowered TG. TC. LDL cholesterol, the LDL-HDL cholesterol ratio, and insulin and raised HDL cholesterol (all P < 0.05). Weight loss lowered TG. TC. LDL cholesterol, and insulin (all P < 0.01) but did not change HDL cholesterol or the LDL-HDL cholesterol ratio. The results suggest that reduction to a weight-steady nonobese state significantly lowers TG, TC, and LDL cholesterol but does not improve HDL cholesterol or the LDL-HDL cholesterol ratio.