Sugars occur naturally in foods and provide energy in the form of carbohydrates, which are an important part of the diet. Fructose is a naturally occurring sugar found in fruit but is also more than half of the composition of high-fructose corn syrup, an added sweetener. Another added sweetener, sucrose, is manufactured from sugar cane or sugar beet and is most commonly referred to as simply sugar.
Identification
Pure fructose is a monosaccharide, or single sugar, and although fructose is what sweetens fruit, it is more frequently consumed in the American diet as high-fructose corn syrup, or HFCS-55. This substance is 55 percent fructose and 45 percent glucose. Sucrose, meanwhile, is a disaccharide composed of 50 percent glucose and 50 percent fructose.
Function
When sucrose is digested, it is broken down into glucose and fructose. Glucose is the only fuel for the brain and the primary fuel for muscles, so excess blood glucose gets stored in the liver and muscles for future use. The body maintains fairly level amounts of glucose in the blood by regulating hormones, such as insulin. Fructose does not require insulin to be used by the body but is metabolized in the liver. The body’s use of fructose is dependent on the level of glucose in the blood, and fructose can be metabolized into glucose if needed.
Effects
A 2009 study published in the "Journal of Clinical Investigation" compared obese individuals receiving a beverage sweetened either by glucose or fructose for 10 weeks, providing 25 percent more calories than their regular diets.
Both groups exhibited similar weight gain due to the additional calories. Only the fructose group gained significant adipose fat--or fat around the belly--which increases risk for cardiovascular disease. The glucose group experienced increased visceral fat, which is fat under the skin.
Although both groups experienced increased lipid metabolism, the study showed that fructose increased levels of 23-hour triglycerides, fasting cholesterol and fasting LDL, or "bad cholesterol," more than glucose. Fructose also decreased insulin sensitivity, whereas glucose did not. It should be noted that fructose alone is not typically used as a sweetener, and the authors state it is uncertain whether the adverse effects of high-fructose corn syrup and sucrose are diluted by their lower fructose content.
History
The use of added sugars and sweeteners grew 19 percent from 1970 to 2005, according to the Department of Agriculture's Assessment of Major Trends in Food Consumption study. The annual per capita availability of corn sweetener and added sugar in 1970 was 114 lbs., compared with 141 lbs. in 2005. In this time period, use of refined cane and beet sugar declined 38 percent, but per capita use of annual corn sweeteners grew by 387 percent. This growth in corn sweetener was fueled by the rise of high-fructose corn syrup's share of all corn sweeteners, which grew from 3 percent to 76 percent in that time period.
Considerations
The Dietary Guidelines for Americans, developed jointly by the Agriculture Department and the Department of Health and Human Services, does not recommend a specific quantity of added sugars in the diet. But the USDA does advise Americans to choose and prepare foods and beverages with little added sugar or sweetener.
The guidelines include a discretionary calorie allowance for added sugar and solid fats. On a 2,000 calorie diet split between the two, this would allow for 8 tsp. per day of added sugar or sweetener. According to the USDA consumption study, daily use of sugars and sweeteners was 30 tsp. per person in 2005. Consuming nutrient-dense foods, such as fruits, vegetables, whole grains and dairy products, provides sugars in moderation.
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