Fructose is a monosaccharide, or single sugar, with the same chemical formula as glucose but a different molecular structure. It is often called fruit sugar and is found in fruit, some vegetables, honey, and other plants.
Sucrose is a disaccharide that contains equal parts of glucose and fructose. Sucrose or table sugar is found naturally in sugar cane and sugar beets. Other sugars in foods and beverages include lactose (glucose and galactose), maltose (two units of glucose), dextrose (another name for glucose), corn syrup (single glucose units) and high-fructose corn syrup (glucose and fructose).
Sugars contain the same number of calories (4 calories per gram) but are metabolized and used by the body in different ways. For instance, glucose from dietary sources is digested, absorbed, transported to the liver, and released into the general blood stream. Many tissues use the glucose for energy; this process requires insulin. Fructose is predominantly metabolized in the liver, but unlike glucose it does not require insulin to be used by the body.
High fructose corn syrup (HFCS) is a liquid sweetener used in the manufacture of foods and beverages. In the late 1960s scientists developed a process that changes dextrose (glucose) from cornstarch into a mixture of fructose and glucose. The most common form (70% in food supply) is HFCS-55, which contains 55% fructose and 45% glucose. By comparison, sucrose contains 50% fructose and 50% glucose. Total deliveries of all caloric sweeteners have increased 25% from 1966 to 2003.
Dr. Robert H. Lustig, a professor of pediatrics and an obesity specialist at the University of California, San Francisco is a researcher sounding the alarm on the rising use of all caloric sweeteners in a recent New York Times article called “Is Sugar Toxic?” You can see a video of his lecture on You Tube.
In the 1800s and early 1900s, the average American took in about 15 grams of fructose (about half an ounce), mostly from eating fruits and vegetables. Today we average 55 grams per day (73 grams for adolescents). The increase in fructose intake is worrisome, says Lustig, because it suspiciously parallels increases in obesity, diabetes, and a new condition called nonalcoholic fatty liver disease that now affects up to one-third of Americans.
When fructose is broken down in the liver, triglycerides are formed. When carbohydrates are in excess, triglycerides can build up in liver cells and damage liver function. Triglycerides released into the bloodstream at high levels are considered a risk for heart disease.
Uric acid is also formed. Uric acid can turn off production of nitric oxide, a substance that helps protect artery walls from damage and contribute to high blood pressure.
It has been argued that these two sweeteners have identical effects on the body, but a recent study suggests otherwise. The study published in Metabolism took a closer look at HFCS and sucrose and was authored by Dr. MyPhuong Le (a postdoctoral fellow at the University of Colorado) and Dr. Julie Johnson, a Professor of Pharmacogenomics at the University of Florida.
They found that fructose was absorbed differently into the bloodstream. The reason may be that sucrose with its 50/50 ratio of glucose and fructose is naturally bonded together as a disaccharide (double sugar) and HFCS is a mixture of free fructose (55%) and free glucose (45%). The key word here is “free”, i.e. not bonded together as in sucrose.
The study examined 40 men and women who were given 24 ounces of HFCS or sugar-sweetened soft drinks. The results showed that the HFCS produced significantly higher fructose levels in the blood than the sugar-sweetened drinks. The HFCS drinks also increased uric acid levels implicated in blood pressure. In this study, the HFCS drinks also resulted in a 3 mm Hg greater rise in systolic blood pressure.
Another recent study found that teens that consume large amounts of fructose in foods and beverages show evidence of heart disease and diabetes risk in their blood. The study published in the February issue of the Journal of Nutrition involved 559 teens aged 14 to 18 found that diets high in fructose were associated with higher blood pressure, diabetes-related measures such as higher fasting blood glucose and insulin resistance, and inflammatory factors that contribute to vascular diseases. The study also found that these teens also had lower levels of HDL (good) cholesterol. These results were more pronounced in the kids with excess belly fat.
There are no specific dietary requirements or recommendations for fructose. The Institute of Medicine (IOM) also found that diets with more than 25% of caloric intake from added sugars from processing were associated with significantly decreased levels of essential nutrients (e.g., calcium, magnesium, and zinc) in some population groups.
As the nation’s obesity crisis continues, the 2010 Dietary Guidelines recommend drinking water instead of sugary drinks like soda and consume little or no added sugar. However, there are no specific guidelines or mention of high fructose corn syrup.
Many nutrition “experts” say there is no association with sugar intake or any significant differences between calorie sweeteners. ”High fructose corn sweeteners do not appear to contribute to overweight and obesity any differently from other energy sources. Critical reviews in Food, Science and Nutrition state that calories are calories and high fructose corn sweeteners are no different than other calories, calorie per calorie…”
However, the Corn Refiners Association said the same thing in their $30 million, 18-month TV ad campaign “targeting mothers” with the message that HFCS is: Made from corn, has no artificial ingredients, is fine in moderation, and is no more fattening than sugar. This may turn out to be true, but what other effects are subtly occurring to the increase in this sweetener whether from sucrose or HFCS. Interesting, the Corn Refiners are requesting a name change from high fructose corn sugar to plain old corn sugar – I wonder why?