Clearing up the confusion about sugar

Q. I realize that sugar is present in many foods, but I find the terminology confusing regarding sugar that is in food and in our bodies as well as how sugar relates to carbohydrates and fiber. I would appreciate an explanation of these terms and information about whether there is a daily allowance for food sugar.

P.S., Walnut Creek, Calif.

A. It becomes confusing when scientific terminology does not mesh with everyday jargon, and the problem applies to certain aspects of carbohydrates.

Let's start with carbohydrates, a broad term for a class of nutrients that is the most plentiful in nature. The word comes from the Latin "carbo" for carbon, and "hydras," which refers to water. As a group, carbohydrates constitute the body's most important source of energy, and there are three basic types: simple carbohydrates, complex carbohydrates and fiber.

When speaking of sugar in reference to food, we tend to be talking about the compound known as sucrose. Sucrose is referred to as a compound because it is a double sugar made up of two single sugars - glucose and fructose - joined together.

The scientific term for sugar is saccharide, from the Greek term "sacchar" for sugar. Saccharin, the oldest artificial sweetener, takes its name from this term. By this system, sucrose is also referred to as a disaccharide, while glucose and fructose are known as monosaccharides. Simple carbohydrates include monosaccharides and disaccharides. Other simple carbohydrates include lactose, or milk sugar, and maltose, which is found in grains and malt beverages, such as beer.

Complex carbohydrates, also known as polysaccharides, are long chains of sugar molecules that are sometimes thousands of sugars long. Starch is an example of a complex carbohydrate.

To complete the picture, we have fiber, an umbrella term referring to a group of complex carbohydrates that have no caloric value because they cannot be digested.

Glucose is the body's most important carbohydrate, and it is often referred to as "blood sugar." Fructose, also known as fruit sugar, is the main sweetener found in fruits.

Glucose is the part of sucrose that can be used directly. It serves as the body's primary source of energy. Glucose is the only fuel used by the red blood cells, and it's the preferred fuel of the brain. A small amount of glucose is made into glycogen, a special glucose reserve found in muscles and in the liver.

Despite these important roles, there is no daily allowance for glucose or sucrose, as they are not essential. Any digestible carbohydrate, such as bread, pasta or rice, can supply the glucose we need. In a pinch, even our own protein can be broken down and changed into glucose. (That's precisely what happens during starvation or intense muscular work.)

While there is no daily value, it is reasonable to set a limit of 8 percent of the daily calories for sucrose and other simple carbohydrates. For a person on a 2,000-calorie diet, that would be a max of 40 grams (10 teaspoons) of sugar in all the foods consumed during the day.

Send questions to: "On Nutrition," Ed Blonz, c/o Newspaper Enterprise Association, 200 Madison Ave., New York, NY 10016 or ed@blonz.com. Due to the volume of mail, personal replies cannot be provided.