OBJECTIVE—To determine the effects of exercise, without weight loss, on insulin sensitivity (S_I), postheparin plasma lipase activity (PHPL), intravenous fat clearance rate (K₂), and fasting lipids in sedentary adults.

RESEARCH DESIGN AND METHODS—At baseline and after 6 months of walk training (intensity 45–55 or 65–75% heart rate reserve, frequency 3–4 or 5–7 days/week, duration 30 min/session), anthropometric indexes, S_I, PHPL, K₂, and fasting lipids were measured in 18 sedentary adults (12 women, 6 men; 51.9 ± 5.8 years of age, BMI 28.9 ± 4.6 kg/m²).

RESULTS—Exercise increased S_I (2.54 ± 2.74 vs. 4.41 ± 3.30 μU · ml⁻¹ · min⁻¹, P < 0.005) and both lipoprotein lipase (LPL) (1,890 ± 1,380 vs. 4,926 ± 1,858 nEq free fatty acid [FFA] · ml⁻¹ · h⁻¹) and hepatic lipase (HL) activities (3,326 ± 1,605 vs. 4,636 ± 1,636 nEq FFA · ml⁻¹ · h⁻¹) (both P < 0.001), without altering BMI, waist circumference, K₂, or fasting lipids. Correlations between changes in LPL and the total:HDL cholesterol ratio (r = −0.54) and changes in the LPL:HL ratio and waist circumference (r = −0.50) were significant (P < 0.05).

CONCLUSIONS—Exercise, without weight loss, increases S_I and PHPL activity in previously sedentary adults, without changing K₂ or fasting lipid levels. Furthermore, increased LPL is associated with a decreased total:HDL ratio, and an increased LPL:HL ratio is associated with a decreased waist circumference. Therefore, even modest amounts of exercise in the absence of weight loss positively affect markers of glucose and fat metabolism in previously sedentary, middle-aged adults.