Question

Describe the role of high fructose corn syrup (55% fructose, 45% glucose) in increased weight gain and atherosclerosis. Also, explain why fructose from fruit does not have the same effect.

Answer 1

Fructose is found in a variety of foods. In table sugar, it is bound to glucose to form the disaccharide sucrose, whereas in honey it occurs in monosaccharide form. In fruit, berries, and vegetables, fructose occurs in both monosaccharide and disaccharide forms. HFCS(high fructose corn syrup) is produced by isomerizing most of the glucose in corn syrup to fructose and then mixing this syrup with varying amounts of corn-based glucose syrup. HFCS-55, consisting of 55% fructose and 42% glucose, is used primarily in sweetened beverages, whereas HFCS-42 (42% fructose; 53% glucose) is used primarily to sweeten other products (e.g., baked foods and confectionaries).A significant increase in fructose absorption has been shown when fructose is coingested with equal amounts of glucose.

Fructose metabolism is also known for its lipogenic potential. On entry into the liver, it is broken down into dihydroxyacetone phosphate and glyceraldehyde-3-phosphate. The former ultimately becomes the glycerol backbone of triglycerides, and the latter produces the acetyl-CoA units required for de novo lipogenesis and the synthesis of fatty acids. Thus, hepatic fructose metabolism can produce the 2 required components for triglyceride synthesis. Importantly, this pathway is unaffected by the regulatory step of glycolysis, phosphofructokinase, meaning that when exposed to high levels of fructose, it is metabolized by the liver unabated and thus rapidly increases triglyceride synthesis. Repeated consumption of high levels of fructose over the short term has been shown to increase fasting levels of triglycerides in a variety of human populations.It appears that high fructose intake can create an unfavorable lipid profile in blood via DNL( De Novo Lipogenesis) .The main product of DNL is palmitic acid, a fatty acid specifically shown to increase the risk of atherosclerosis .Another possible difference between fructose and glucose on risk factors for atherosclerosis is the effect of these sugars on blood uric acid level. Increased uric acid level has been associated with atherosclerosis .

Fruit is a minor source of fructose in the diet compared to added sugars. The harmful effects of fructose apply to a Western diet supplying excess calories and added sugars. It does not apply to the natural sugars found in fruits and vegetables.