THE METABOLIC SYNDROME - FROM INHERITED SURVIVAL TRAIT TO A HEALTH-CARE PROBLEM

A critical role is proposed for the quantity and quality of dietary ca rbohydrate in the pathogenesis of the insulin resistance and hyperinsu linaemia which characterise the Metabolic Syndrome. We propose that an insulin-resistant genotype evolved to provide survival and reproducti ve advantages for the cold-climate, large game hunters of the last Ice Age who consumed a low carbohydrate, high protein diet with periodic starvation. Insulin resistance would have minimised glucose utilisatio n by muscles thereby facilitating the preferential utilisation of gluc ose by the brain, foetus and mammary gland. But beginning about 10,000 years ago following the end of the last Ice Age and the development o f agriculture, dietary carbohydrate increased and the selection pressu re for insulin resistance decreased in some groups. Agriculture began in the Middle East and spread throughout Europe long before it was dev eloped elsewhere. Hence the prevalence of the insulin-resistant genoty pe decreased in Europeans and other groups exposed to a high carbohydr ate intake for sufficiently long. Some geographically isolated groups such as the Pima Indians and Nauruans experienced conditions which fur ther diminished the gene pool diversity and resulted in particularly i nsulin resistant populations. Traditional carbohydrate foods have a lo w glycaemic index and produce only modest increases in plasma insulin. However, the constant supply of highly refined high glycaemic index c arbohydrate in modern diets, results in postprandial hyperinsulinaemia . The insulin-resistant genotype is now disadvantageous and predispose s to the development of the Metabolic Syndrome.