By Philip Reeves

Obesity and Type 2 diabetes occur in the United States at alarming rates. Many nutritionists and health care professionals are convinced that these conditions are caused in large part by recent changes in our diet and to reduced physical activity.

Some believe that the major change in the diet related to these problems is an increase in the availability and consumption of fructose, a simple sugar that makes up half of sucrose (table sugar), and high-fructose corn syrup (HFCS). Over the past 30 years, consumer consumption of caloric sweeteners in the form of sucrose and HFCS has increased from about 6 ounces to 8 ounces /person/day. Consumption of HFCS containing free fructose increased from zero to 3 ounces/person/day, in the same period, while the use of sucrose decreased. We now consume as much HFCS as we do sucrose.

Most commercial HFCS added to foods contains either 42% free fructose and 55% free glucose or 55% free fructose and 42% free glucose, depending on its use. In comparison, sucrose contains 50% fructose and 50% glucose. HFCS is used extensively in soft drinks, fruit drinks, baked goods, and many other manufactured food products. A 12-fluid ounce sweetened soft drink, for example, contains about 1.3 ounces of corn syrup, which replaces a similar amount of sucrose that was used almost exclusively in these beverages before the 1970s.

HFCS is made from natural cornstarch by using an enzyme to convert the starch to glucose. Then some of the glucose is converted to fructose with another enzyme. The finished product contains a mixture of free glucose and free fructose in the proportions listed above. Manufacturers like to use HFCS in food processing because it mixes well with most types of food ingredients. It also lends soft texture and browning ability to cookies and other baked goods, and it is less expensive than sugar.

Some health care professionals believe that the connection between high fructose consumption and obesity and Type-2 diabetes involves the way fructose is broken down in the body. After fructose is absorbed into the body from the intestine, it is carried to the liver and made into smaller sugars that can readily form fats. Thus, the more fructose you consume the more is forced into fat. As the fat builds up in the blood, they begin to impair the actions of insulin, which normally signals the body to use glucose to produce energy. It is thought that such suppression over time makes the body resistant to insulin. As a result, glucose builds up in the blood, initiating Type-2 diabetes.

Although there is strong evidence from studies with laboratory animals that feeding fructose can cause chronic increases in blood lipids, the effects are not that clear in humans. Some short-term human studies have shown increases in blood cholesterol and undesirable changes in cardiovascular risk factors when subjects were fed fructose at the level of 15% of their daily calories. For a person eating 2,000 calories per day, this would amount to about 2.6 ounces of fructose (or 3½ twelve fluid-ounce cans of sweetened soft drink). However, other studies have shown no effects of fructose consumption on blood triglycerides and cholesterol. Thus, more long-term human studies are needed to settle this issue.

In the meantime, moderation is one of the keys to good dietary practices. For dietary carbohydrates, the new 2005 USDA Dietary Guidelines (http://www.health.gov/dietaryguidelines/dga2005/document/) recommends that individuals choose fiber-rich fruits, vegetables, and whole grains often, and choose and prepare foods and beverages with little added sugars or caloric sweeteners.