Changes in Markers of Insulin Resistance Following a 6-Month Weight Loss Program in Obese Women

Abstract

PURPOSE: To examine the relationship between markers of insulin resistance prior to and following a 6-month weight loss program in obese women. METHODS: One hundred eighty five (N=1 85) overweight and obese (BMI = 32.7+4.2 kg/m2; age = 37.7+5.6 years) women participated in a 6-month weight loss intervention to examine the impact of different doses (moderate: 1000 vs. high: 2000 kcal/wk) and intensities (moderate: 55–69% HRmax vs. vigorous: 70–85% HRmax) of exercise on weight loss, fitness, and biomarkers of insulin resistance. Subjects were randomly assigned to one of the following exercise conditions: 1) moderate dose, moderate intensity; 2) moderate dose, vigorous intensity; 3) high dose, moderate intensity; high dose, vigorous intensity). All groups reduced energy intake to 1200 to 1500 kcal/d, and received a group-based behavioral weight loss intervention. Assessments at baseline and 6 months included body weight, fitness using a submaximal graded exercise test to 85% of HRmax, and fasting blood samples for glucose and insulin, which were used to compute HOMA-IR. RESULTS: Analysis revealed no significant difference between the exercise groups for change in body weight, fitness, or markers of insulin resistance. Overall, there was a significant decrease in body weight (8.4+4.8 kg; 9.7+5.4%), increase in fitness as measured by time to achieve 85% HRmax (3.8+3.1 min), decrease in fasting insulin (3.8+8.2 μU/ml), and decrease in HOMA-IR (0.7+2.4) (p <0.001). Change in fitness was not significantly correlated with change in fasting insulin or HOMA-IR. However change in body weight was significantly correlated with reductions in fasting insulin (r=0.14; p <0.05) and HOMA-IR (r=0.17; p <0.05). CONCLUSION: In this sample of overweight and obese women, weight loss rather than improvements in cardiorespiratory fitness were associated with improvements in markers of insulin resistance. Thus, while exercise is important to improve fitness in overweight adults, it may be important for exercise to elicit significant reductions in body weight to have the greatest impact on insulin resistance. However, because of the modest correlations between change in body weight and markers of insulin resistance, this suggests that additional factors contribute to insulin resistance in overweight adult women.