Background: Insulin sensitivity (Si) is improved by weight loss andexercise, but the effects of the replacement of saturated fatty acids (SFAs)with monounsaturated fatty acids (MUFAs) or carbohydrates of high glycemicindex (HGI) or low glycemic index (LGI) are uncertain.
Objective: We conducted a dietary intervention trial to studythese effects in participants at risk of developing metabolic syndrome.
Design: We conducted a 5-center, parallel design, randomizedcontrolled trial [RISCK (Reading, Imperial, Surrey, Cambridge, and Kings)]. Theprimary and secondary outcomes were changes in Si (measured by using anintravenous glucose tolerance test) and cardiovascular risk factors.Measurements were made after 4 wk of a high-SFA and HGI (HS/HGI) diet and aftera 24-wk intervention with HS/HGI (reference), high-MUFA and HGI (HM/HGI), HMand LGI (HM/LGI), low-fat and HGI (LF/HGI), and LF and LGI (LF/LGI) diets.
Results: We analyzed data for 548 of 720 participants who were randomly assigned to treatment. The median Si was 2.7 × 10−4 mL · μU−1 · min−1(interquartile range: 2.0, 4.2 × 10−4 mL · μU−1 · min−1), and unadjusted mean percentage changes (95% CIs) after 24 wk treatment (P = 0.13) were as follows:for the HS/HGI group, −4% (−12.7%, 5.3%); for the HM/HGI group, 2.1% (−5.8%,10.7%); for the HM/LGI group, −3.5% (−10.6%, 4.3%); for the LF/HGI group, −8.6%(−15.4%, −1.1%); and for the LF/LGI group, 9.9% (2.4%, 18.0%). Total cholesterol (TC), LDL cholesterol, and apolipoprotein B concentrationsdecreased with SFA reduction. Decreases in TC and LDL-cholesterolconcentrations were greater with LGI. Fat reduction lowered HDL cholesterol andapolipoprotein A1 and B concentrations.
Conclusions: This study did not support the hypothesis that isoenergeticreplacement of SFAs with MUFAs or carbohydrates has a favorable effect on Si.Lowering GI enhanced reductions in TC and LDL-cholesterol concentrations insubjects, with tentative evidence of improvements in Si in the LF-treatmentgroup. This trial was registered at clinicaltrials.gov as ISRCTN29111298.