Fasting serum insulin and the homeostasis model of insulin resistance (HOMA-IR) in the monitoring of lifestyle interventions in obese persons

Objectives:Lifestyle changes with increased physical activity and balanced energy intake are recognized as the principal interventions in obesity and insulin resistance. Only few prospective studies, however, have so far addressed the potential role of routine biochemical markers of insulin sensitivity in the monitoring of respective interventions.Design and methods:Fasting insulin and glucose was measured in 33 obese individuals undergoing a lifestyle modification program (MOBILIS) at baseline and after 1 year. The HOMA-IR index (homeostasis model of insulin resistance) was calculated as [fasting serum glucose * fasting serum insulin / 22.5], with lower values indicating a higher degree of insulin sensitivity.Results:While the median body mass index (BMI) and waist circumference decreased by 10% and 11%, respectively, the HOMA-IR index decreased in an over-proportional manner by 45% within 1 year (BMI baseline, median 35.7, interquartile range (IQR) 33.7–37.7; after 1 year, median 32.2, IQR 29.6–35.1. HOMA-IR baseline, median 2.9, IQR 1.5–4.6; after 1 year 1.6, IQR 0.9–2.7). In contrast to HOMA-IR and fasting serum insulin, no significant changes in fasting serum glucose were observed. Baseline and post-intervention HOMA-IR showed a high degree of inter-individual variation with eight individuals maintaining high HOMA-IR values despite weight loss after 1 year of intervention.Conclusions:Individual changes in the carbohydrate metabolism achieved by a lifestyle intervention program were displayed by fasting serum insulin concentrations and the HOMA-IR but not by fasting glucose measurement alone. Therefore, assessment of the HOMA-IR may help to individualize lifestyle interventions in obesity and to objectify improvements in insulin sensitivity after therapeutic lifestyle changes.