N02031: Impact of the amount and composition of dietary fat and carbohydrate on metabolic syndrome and cardiovascular disease risk

Study Duration: January 2004 to January 2008

Contractor: MRC-HNR, Cambridge

There is evidence that the amount and quality of dietary fat and carbohydrate can modify some features of the metabolic syndrome including blood lipids, insulin resistance, hypertension and endothelial function. A key scientific and public health question is whether reducing intakes of saturated fats (SFA) via low fat, high carbohydrate diets, or by moderate fat diets in which saturated fats are substituted with monounsaturated fats (MUFA), have differential effects on risk factors for the metabolic syndrome. Whilst randomised controlled trials have helped elucidate the impact of these regimens on lipid risk factors, this has not been the case for insulin sensitivity. Moreover it is presently unclear whether the adverse effects of high carbohydrate diets on lipid risk factors, via heightened insulin and glucose responses, can be alleviated by the substitution of foods with lower glycaemic index. This study addresses the comparative effects of these diets in a suitably powered intervention on insulin sensitivity. It will also consider some additional aspects of the metabolic syndrome in order to provide a comprehensive analysis to inform public nutrition policy.

A total of 650 subjects will be recruited into the study, 130 in each of the 5 collaborative centres: MRC Human Nutrition Research, Cambridge; Imperial College, London; Kings College, London; University of Reading; University of Surrey. Subjects will be selected on the basis of their increased risk for developing the metabolic syndrome and its associated cardiovascular risk factors. Subjects will be recruited as two cohorts (~ n=65) at each centre.

The dietary intervention will invole the manipulation of: total dietary fat (~38% vs. ~28%) and its composition (i.e. SFA vs. MUFA); and total dietary carbohydrate (~45% vs. ~55%) and its composition (i.e. high vs. low glycaemic index) using a controlled, single blind, parallel design with 5 treatment arms. Six hundred and fifty subjects will be recruited and assigned to a control group or one of four experimental groups for a period of 24 weeks, with a run-in period of 4-weeks.