Intensive Lifestyle Changes Are Necessary to Improve Insulin Sensitivity

Abstract

OBJECTIVE -The extent to which lifestyle must be altered to improve insulin sensitivity has not been established. This study compares the effect on insulin sensitivity of current dietary and exercise recommendations with a more intensive intervention in normoglycemic insulinresistant individuals.RESEARCH DESIGN AND METHODS -Seventy-nine normoglycemic insulinresistant (determined by the euglycemic insulin clamp) men and women were randomized to either a control group or one of two combined dietary and exercise programs. One group (modest level) was based on current recommendations and the other on a more intensive dietary and exercise program. Insulin sensitivity was measured using a euglycemic insulin clamp, body composition was measured using dual-energy X-ray absorptiometry, and anthropometry and aerobic fitness were assessed before and after a 4-month intervention period. Four-day dietary intakes were recorded, and fasting glucose, insulin, and lipids were measured.RESULTS -Only the intensive group showed a significant improvement in insulin sensitivity (23% increase, P ϭ 0.006 vs. 9% in the modest group, P ϭ 0.23). This was associated with a significant improvement in aerobic fitness (11% increase in the intensive group, P ϭ 0.02 vs. 1% in the modest group, P ϭ 0.94) and a greater fiber intake, but no difference in reported total or saturated dietary fat.CONCLUSIONS -Current clinical dietary and exercise recommendations, even when vigorously implemented, did not significantly improve insulin sensitivity; however, a more intensive program did. Improved aerobic fitness appeared to be the major difference between the two intervention groups, although weight loss and diet composition may have also played an important role in determining insulin sensitivity. Diabetes Care 25:445-452, 2002L ifestyle intervention reduces the risk of progression from impaired glucose tolerance (IGT) to type 2 diabetes (1). It is widely assumed that current advice regarding physical activity (2) and dietary modification (3) is sufficient (presumably mediated via an improvement in insulin sensitivity) to reduce the risk of type 2 diabetes. All the large intervention trials either underway or completed have focused on intervention in subjects with IGT (1,4,5). However, it appears that once abnormal glucose levels have developed, significant ␤-cell dysfunction has already occurred, and there is less chance of improving insulin sensitivity (6).Intervention before IGT has developed may offer the best opportunity to reduce progression to IGT and type 2 diabetes. Although increased physical activity and dietary modification have been shown to improve insulin sensitivity, there are no data that clearly show the extent of lifestyle change required. This study is the first to compare two levels of practical lifestyle intervention in normoglycemic insulin-resistant individuals on insulin sensitivity, one based on current recommendations (modest) and the other on a more intensive dietary and exercise program. This will help to answer the importa...

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