Objective: To compare and assess the single and joint effect of diet and exercise intervention for 1 year on insulin resistance and the development leading toward the insulin resistance syndrome.
Research design and methods: An unmasked, randomized 2 x 2 factorial intervention trial was applied with a duration of 1 year for each participant. The trial comprised 219 men and women with diastolic blood pressure of 86-99 mmHg, HDL cholesterol < 1.20 mmol/l, triglycerides > 1.4 mmol/l, total cholesterol of 5.20-7.74 mmol/l, and BMI > 24 kg/m2. Participants were randomly allocated to diet group (n = 35), diet and exercise group (n = 67), exercise group (n = 54), and control group (n = 43). The diet included increased intake of fish and reduced total fat intake. The exercise program entailed supervised endurance exercise three times a week. Baseline cross-sectional changes and 1-year changes in insulin resistance, fasting serum levels of insulin, C-peptide, proinsulin, glucose, and lipids as well as weight, mean blood pressure, and plasminogen activator inhibitor 1 (PAI-1) values were recorded.
Results: The cross-sectional results at baseline showed significant correlations between the calculated insulin resistance and BMI (r = 0.54) and correlations between the mean blood pressure (mBP) (r = 0.26) and PAI-1 (r = 0.40). The 1-year diet intervention gave a significant decrease in the calculated insulin resistance from 4.6 to 4.2 and a positive correlation between the changes in insulin resistance and changes in BMI (r = 0.40). The diet and exercise intervention also led to significantly decreased insulin resistance (from 5.0 to 4.0). The exercise intervention did not significantly change insulin resistance.
Conclusions: The cross-sectional and 1-year intervention results supported each other and underscored the important connection between increased BMI and the development leading toward the insulin resistance syndrome.