Increases in the use of high fructose corn syrup (HFCS) as a sweetener mirror the rise in obesity seen in Western nations over the last four decades. High fructose corn syrup is produced by isomerising a large proportion of the glucose molecules in corn syrup into fructose. This isomerised syrup is them mixed with varying amounts of glucose corn syrup to produce syrup with differing amounts of fructose. High fructose corn syrup-55 consists of 55 % fructose and 42 % glucose and is used mainly in soft drinks. High fructose corn syrup-42 consists of 42 % fructose and 53 % glucose and is used mainly in baked foods, sweets and cakes1. The increase in the use of HFCS to sweeten foods in potentially detrimental because fructose consumption is linked to the development of insulin resistance and the metabolic syndrome.
Fructose does not stimulate the release of insulin from the β-cells of the islets of Langerhans in the pancreas. Because of the absence of insulin, the absorbed fructose is metabolised in the liver. Here the fructose is broken down to dihydroxyacetone phosphate and glyceralderhyde-3-phosphate, which are converted to glycerol and acetyl-CoA respectively (here). These provide the building block for de novo lipogenesis and the synthesis of fatty acids, which results ultimately in fructose increasing circulating levels of triglycerides. This hepatic metabolism of fructose by-passes the regulatory step of glycolysis because it does not involve phosphofructokinase. This means that production of fatty acids is not regulated by feedback mechanisms. Short term consumption of fructose results in raised fasting levels of triglycerides in humans and these high levels of triglycerides are thought to be the cause of insulin resistance.
In addition, HFCS can raise plasma uric acid levels. This is because fructose is able to upregulate nucleotide metabolism with the result that more uric acid is produced. Elevated levels of uric acid are seen in a number of metabolic disorders, including metabolic syndrome. Rats fed diets high in fructose as 60 % of energy showed increased fasting triglycerides, increased blood pressure, and insulin resistance, but these effects disappeared when uric acid lowering drugs allopurinol or benzbromarone were administered. Therefore a strong link between fructose consumption, high uric acid levels and insulin resistance is provided in the literature. High fructose corn syrup does not stimulate the satiety signal that prevents over eating because the signal relies on feedback from insulin. Therefore consumption of HFCS leads to overeating and obesity.
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