Effect of changing the amount and type of fat and carbohydrate on insulin sensitivity and cardiovascular risk: the RISCK (Reading, Imperial, Surrey, Cambridge, and Kings) trial.
BACKGROUND
Insulin sensitivity (Si) is improved by weight loss and exercise, but the effects of the replacement of saturated fatty acids (SFAs) with monounsaturated fatty acids (MUFAs) or carbohydrates of high glycemic index (HGI) or low glycemic index (LGI) are uncertain.


OBJECTIVE
We conducted a dietary intervention trial to study these effects in participants at risk of developing metabolic syndrome.


METHODS
We conducted a 5-center, parallel design, randomized controlled trial [RISCK (Reading, Imperial, Surrey, Cambridge, and Kings)]. The primary and secondary outcomes were changes in Si (measured by using an intravenous glucose tolerance test) and cardiovascular risk factors. Measurements were made after 4 wk of a high-SFA and HGI (HS/HGI) diet and after a 24-wk intervention with HS/HGI (reference), high-MUFA and HGI (HM/HGI), HM and 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 concentrations decreased with SFA reduction. Decreases in TC and LDL-cholesterol concentrations were greater with LGI. Fat reduction lowered HDL cholesterol and apolipoprotein A1 and B concentrations.


CONCLUSIONS
This study did not support the hypothesis that isoenergetic replacement of SFAs with MUFAs or carbohydrates has a favorable effect on Si. Lowering GI enhanced reductions in TC and LDL-cholesterol concentrations in subjects, with tentative evidence of improvements in Si in the LF-treatment group. This trial was registered at clinicaltrials.gov as ISRCTN29111298.
Jebb
Susan A
SA
Medical Research Council Human Nutrition Research, Elsie Widdowson Laboratory, Cambridge, United Kingdom. susan.jebb@mrc-hnr.cam.ac.uk
Lovegrove
Julie A
JA
Griffin
Bruce A
BA
Frost
Gary S
GS
Moore
Carmel S
CS
Chatfield
Mark D
MD
Bluck
Les J
LJ
Williams
Christine M
CM
Sanders
Thomas Ab
TA
D000328:Adult; D000368:Aged; D016632:Apolipoprotein A-I / Q000097:blood; D001055:Apolipoproteins B / Q000097:blood; D002318:Cardiovascular Diseases / Q000453:epidemiology*; D002784:Cholesterol / Q000097:blood; D008076:Cholesterol, HDL / Q000097:blood; D004040:Dietary Carbohydrates / Q000494:pharmacology*; D004041:Dietary Fats / Q000494:pharmacology*; D004739:England / Q000453:epidemiology; D005227:Fatty Acids / Q000494:pharmacology; D005260:Female; D005951:Glucose Tolerance Test; D006801:Humans; D007328:Insulin / Q000502:physiology*; D008297:Male; D024821:Metabolic Syndrome / Q000453:epidemiology; D008875:Middle Aged; D012107:Research Design; D012307:Risk Factors
D016632:Apolipoprotein A-I; D001055:Apolipoproteins B; D008076:Cholesterol, HDL; D004040:Dietary Carbohydrates; D004041:Dietary Fats; D005227:Fatty Acids; D007328:Insulin; D002784:Cholesterol