Fructose No Substitute for Glucose in Diabetes

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By Kristina Fiore, Staff Writer, MedPage Today Published: December 07, 2011

NEW YORK -- Although it negates the dumping of glucose directly into the bloodstream, fructose may not be an ideal sweetener for diabetics, researchers said here. Its links with hypertension, adiposity, and increased uric acid levels could potentially outweigh its immediate blood sugar benefits, especially among patients with diabetes, who already have or are at risk for such comorbidities, according to James Rosenzweig, MD, of Boston University. "There are conflicting results," regarding the effects of fructose, Rosenzweig said at a press briefing here arranged by the Endocrine Society. "But fructose itself may have metabolic risks compared with glucose." Fructose, which is the main sugar found in fruits, is a monosaccharide, like glucose. But unlike glucose, which requires insulin to move it into the body's muscle tissue where it's processed into energy, fructose is metabolized by the liver. There, it's converted into glycogen, a starch, and lipids, Rosenzweig explained. Some researchers have speculated that since it negates the need for insulin, it may serve as an ideal replacement for glucose in diabetics' diets. But several recent studies have scrutinized its effects on metabolism -- some of which could add to comorbidities already seen in this population. Some studies have shown that fructose intake is linked with higher levels of serum triglycerides, potentially contributing to adiposity and weight gain, Rosenzweig said. It's also been tied to increased levels of uric acid, which can lead to gout and kidney stones, he said. Chronically high levels of uric acid have also been linked with atherosclerosis, which Rosenzweig said is troubling given that hardening of the arteries is already a known complication of diabetes itself. And fructose overload also may be associated high blood pressure – another common comorbidity among diabetics -- and some of that data have come from large-scale epidemiological studies such as the National Health and Nutrition and Examination Survey. The same problems could be associated with high-fructose corn syrup, which is a polysaccharide that's chemically similar to plain table sugar, or sucrose. The molecule is half fructose and half glucose, but the gastrointestinal tract breaks it down into its respective monosaccharides, Rosenzweig said. Thus, diabetics get the initial dumping of blood glucose, plus the liver hit of fructose, which generates lipids, he explained, adding that there's no discernible metabolic difference between sucrose and high-fructose corn syrup. He cautioned that some of the studies have involved large doses of fructose -- far larger than what would represent a normal intake -- so the effects could be exaggerated. Moreover, the American Diabetes Association doesn't recommend fructose as a substitute sweetener for glucose, he said. It does, however, recommend fruit intake as part of a healthy diet -- though the amount of fructose in fruits is hardly enough to contribute too significantly to obesity, he added. Rosenzweig reported no conflicts of interest.

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