Fructose and Blood Sugar

Fructose is a natural sugar that appears in fruits and as a component of sucrose and high fructose corn syrup. Sucrose, also known as table sugar, contains equal portions of fructose and glucose molecules. Similarly, high fructose corn syrup derives from fructose and glucose, although the fructose proportion is slightly greater. The most common source of carbohydrates, fructose appears exclusively in plants.

Composition and Interactions

Fructose is comprised of six carbon, six oxygen and 12 hydrogen molecules. Yeast and bacteria ferment fructose to produce ethanol, which is why fruit juices are most often converted into alcoholic beverages. Fructose is a white solid that is difficult to crystallize because of its high water solubility. Like other sugars, fructose dehydrates to produce hydroxymethylfurfural, a viable natural fuel comparable to petroleum, characterized by a browning effect when heated. Crystalline sucrose appears very similar to high fructose corn, but it's distinct since it contains only fructose, rather than both fructose and glucose.

Metabolism

Fructose is a simple monosaccharide and, accordingly, the pancreas converts it to glucose by releasing an enzyme called protease. Once glucose, it passes through the digestive system and absorbs into the bloodstream through the small intestine. The liver then releases insulin, which facilitates the transfer of glucose into cells throughout the body to fuel them. The body converts the remaining glucose into fat to store for later use.

Dangers

A diet high in fructose can be dangerous, particularly when combined with other sugars. Ingesting it naturally through fruits in moderate amounts is necessary to provide adequate fuel for somatic cells. However, when ingested in large amounts, even through fruit, fructose can be harmful and lead to weight gain. Fructose in tandem with other sugars, such as in the form of sucrose or in high fructose corn syrup, can be even more dangerous. Fructose converts into glucose and, therefore, directly affects blood sugar levels. Inordinate consumption of fructose in any form will cause rises in serum glucose levels with which the pancreas cannot keep up, resulting in glucose sensitivity. This is a condition where the body becomes incapable of producing enough insulin or ceases secreting it. This condition can be a predictor of diabetes, particularly with a hereditary proclivity or obesity, but it is only one factor that can contribute to dysmetabolic syndrome, according to John P. Bantle and Gérard Slama in "Nutritional Management of Diabetes Mellitus and Dysmetabolic Syndrome."

Comparisons

Fructose is the more dangerous of the three most common monosaccharides in a diet; the other two are glucose and galactose. In a 2009 study by Peter Havel and colleagues at the University of California titled Consuming Fructose Sweetened, Not Glucose Sweetened, Beverages Increases Visceral Adiposity and Lipids and Decreases Insulin Sensitivity in Overweight/Obese Humans that was published in the "Journal of Clinical Investigation," fructose was shown to have a greater chance of causing desensitization to insulin and weight gain when compared with glucose. Accordingly, inordinate consumption of fructose and sugars that contain it, such as sucrose and high fructose corn syrup, have a higher chance of resulting in health difficulties such as heart attacks, strokes and diabetes. Galactose causes the least rise in serum glucose levels.