What is fructose?

Fructose is a monosaccharide, or single sugar, that has the same chemical formula as glucose but a different molecular structure. Sometimes called fruit sugar, fructose is found in fruit, some vegetables, honey, and other plants. Fructose and other sugars are carbohydrates, an important source of energy for the body.

What other types of sugars are there?

The food supply contains a variety of sugars called monosaccharides (single sugar units like fructose and glucose) and disaccharides (two monosaccharides linked together). Glucose is the main source of energy for the body because most complex sugars and carbohydrates break down into glucose during digestion. Starches contain many single sugar units linked together. The various sugars perform different functions in the body, but they all can provide energy.

Sucrose is a disaccharide that contains equal parts of glucose and fructose. Known as table or white sugar, sucrose is found naturally in sugar cane and sugar beets. Other sugars in foods and beverages include:

Is fructose safe?

Fructose is “generally recognized as safe” by the Food and Drug Administration (FDA).

The Surgeon General's Report on Nutrition and Health, the National Academy of Sciences report Diet and Health, and Healthy People 2000: National Health Promotion and Disease Prevention Objectives by the U.S. Department of Health and Human Services support this conclusion.

In a 2002 scientific statement on sugar and cardiovascular disease, the American Heart Association concluded that, for most individuals, consuming fructose either pure or in the form of sucrose has neither beneficial nor adverse effects.

What are the differences in the way glucose and fructose are metabolized by the body?

Even though commonly consumed sugars provide basically the same number of calories, they 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 take up glucose from the blood to use 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.

Does fructose cause diabetes?

Diabetes is a disorder affecting the way the body produces and uses insulin and how it handles blood glucose. Insulin is essential for aiding glucose transport into cells. People with type I diabetes do not produce insulin, whereas those with type II diabetes either do not produce enough insulin or cannot efficiently use the insulin their bodies make. Factors such as overweight and obesity, lack of physical activity, and genetic predisposition all increase the risk for type II diabetes.
People with diabetes must pay attention to the amount of all carbohydrates—sugars and starches—they consume.

Because fructose does not increase blood glucose and does not require insulin, individuals with diabetes can often tolerate it better than other sugars. In fact, studies show that small amounts of oral fructose may actually improve glycemic control in people with diabetes.

Does fructose cause obesity?

Excess body fat results when people do not balance their energy (caloric) input with energy output. Extra calories may come from any caloric nutrient—proteins, fats, alcohol and carbohydrates including starches and sugars such as fructose. Lack of physical activity plays a significant role in promoting body fat accumulation and development of obesity.

Some researchers have speculated that fructose may not be as satiating (produce feeling of fullness) as other carbohydrates because it does not stimulate insulin and leptin secretion nor suppress ghrelin production—all hormones that help to regulate hunger and food intake. However, it is important to note that this speculation is based on preliminary research that tested fructose levels at least three to four times higher than the average amount consumed by Americans. Further, very few Americans ever consume fructose in isolation, but rather in combination with glucose.

Insulin resistance is a condition in which the body does not effectively use the insulin it produces. The body compensates by producing greater amounts of insulin in order to maintain normal blood glucose levels. Insulin resistance—along with obesity, hypertension, and blood lipid disorders—is part of the metabolic syndrome. Insulin resistance sometimes leads to type II diabetes and heart disease.

Although experimental animals fed very large quantities of fructose have developed insulin resistance, feeding studies in humans have never demonstrated this effect. Excess body fat, lack of physical activity and a genetic predisposition are thought to be the primary drivers for developing insulin resistance, not fructose consumption.

What effect does fructose have on triglycerides in the body?

Triglyceride is a technical term for fat that occurs in food and in the body. Both dietary fat and carbohydrates contribute to the formation of triglycerides in the body but in different ways. Excess consumption of calories from fats, proteins, or carbohydrates—including starches and sugars—promotes accumulation of body fat.

Research in humans has shown inconsistent effects of sucrose and fructose on triglycerides in the bloodstream. The variable effects may be related to factors such as the amount of fructose consumed; body weight status; and baseline blood triglyceride, insulin and glucose levels. An elevation in blood triglycerides has been seen mostly in sedentary overweight and obese subjects and with test diets that are high in both fructose and total carbohydrate and low in dietary fiber and fat. Some research suggests that chronic elevation of triglycerides in the bloodstream may increase the risk for insulin resistance and coronary heart disease.

There are no specific dietary requirements or recommendations for fructose. The National Academy of Sciences’ Institute of Medicine (IOM) recommends total carbohydrate intakes should comprise 45 to 65% of calorie intake. Most of the carbohydrates should come from fruits and fruit juices, vegetables, whole grains, legumes, and dairy products or other rich sources of calcium.

The IOM also found that diets with more than 25% of caloric intake from added sugars were associated with significantly decreased levels of essential nutrients (e.g., calcium, magnesium, and zinc) in some population groups. Added sugars are sugars and syrups added to foods during processing or preparation. The IOM did not recommend an ideal level of added sugars consumption.

The newly released 2007 Dietary Guidelines for Americans recommend “choosing and preparing foods and beverages with little added sugars or caloric sweeteners.” Because fructose is a component of most added sugars, moderating the amount of added sugars in the diet will automatically moderate fructose intake. Added sugars do not include the fructose found naturally in fruits and vegetables, which is covered under the consumption levels recommended by the Dietary Guidelines of; 4½ cups per day; 2 cups of fruit, and 2½ cups of vegetables.

All sugars, including fructose, can be included in a health promoting diet if eaten in moderation.