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Monday, July 31, 2006

What's In Your Food: Carbohydrates


Carbohydrates are the body's primary source of fuel (glucose) for energy. This family includes simple carbohydrates (sugars) and complex carbohydrates (starches). Though both types end up as glucose, foods that are high in complex carbohydrates, such as grains and vegetables, usually supply a good-health bonus of vitamins, minerals and fiber.

Meanwhile, simple carbohydrates from candy, cake, table sugar, syrups, sweetened cereals and other sources of concentrated sugar contribute "empty calories" that provide energy, but no nutrients.

Before carbohydrates can be used, they must be broken down in the intestine by the digestive enzymes into simple sugars — glucose, fructose (fruit sugar) and galactose (a component of milk sugar).

Some of the glucose is used immediately for energy; the rest is stored in the liver, muscles and fat cells in the form of glycogen and fat for future use. (Fructose and galactose, however, must first be converted by the liver to glucose.)

After a meal, the hormone insulin, which is produced in the pancreas, lowers the level of glucose in the blood by stimulating body cells to take up and store excess glucose. When your blood sugar is low — say, before breakfast or after exercise — another pancreatic hormone, glucagon, stimulates the conversion of liver glycogen back to glucose, preparing it to be returned to the blood stream.

In diabetes, a shortage or absence of insulin prevents glucose from moving into the cells. Insulin also plays an important role in preventing an excessive release of glucose from the liver in between meals.

Eating sugar doesn't cause the disease — diabetics have to watch their total carbohydrate intake, rather than the type consumed. Eating sugary foods, however, is an easy way to overload the carbohydrate allotment.

In planning your diet, 25 percent to 50 percent of your daily calories should come from carbohydrate sources, with the bulk of these calories supplied by complex carbohydrates.

This means your daily diet should contain:

  • whole grain foods with each meal
  • plenty of vegetables
  • fruit, two to three times per day

It's estimated that American adults get about 20 percent of their daily calories from sugar. On a 2,000-calorie diet, that's about 400 calories (100 grams) or the equivalent of 25 teaspoons of sugar each day! That amounts to about 130 pounds of sugar being consumed by the typical American adult each year.

The obvious way to cut back on refined sugar is to limit the amount of candy, cake, cookies, pies, ice cream and other sweets you eat and to avoid adding table sugar to foods and beverages.

But that's not always so easy, since sugar comes in many forms:
  • Monosaccarides include glucose (sometimes called dextrose), fructose and galactose. All have the same number and types of atoms but each has a different arrangement. The different arrangements of atoms account for the differences in sweetness. Glucose (one of the two sugars in every disaccaride is mildly sweet, fructose (found in fruits and honey) is intensely sweet and galactose (a component of milk sugar) is hardly sweet at all.

  • Disaccharides include sucrose (table sugar), lactose (milk sugar) and maltose (produced in plants and in the human body when starch breaks down). They are all pairs of two monosaccarides: Sucrose is glucose and fructose; lactose is glucose and galactose; and maltose is comprised of two molecules of glucose.

  • Polysaccharides (starches, glycogen, cellulose) don't taste sweet and are composed of hundreds, even thousands, of glucose molecules linked together. They are found in foods such as potatoes, rice and dried beans.

When it comes to overall health, all sugars are created equal. Honey, fructose, sucrose, corn syrup, maple syrup, and molasses are no better (or worse) for you than refined white sugar. Although they may be absorbed differently, all sugars eventually break down in the body and end up as glucose.

While refined white sugar has been blamed for an endless array of health problems (including hypoglycemia or "low blood sugar," depression, yeast infections and hyperactivity), there is no hard evidence to back up these claims.

Sugar, however, does play a role in tooth decay since bacteria in the mouth break down sugar, producing an acid that erodes tooth enamel. But the sugar can just as easily come from the breakdown of starchy foods such as bread and potatoes as it can from candy bars. Sugary foods that stay in your mouth — soft drinks and fruit drinks sipped throughout the day, for example, are worse than sugar added to your morning coffee.

Regular brushing and flossing to remove sugar before the damage occurs is essential to a healthy mouth.

The sugar in carbohydrates contributes to obesity, which is linked to many diseases and disorders, including heart disease, high blood pressure, diabetes, gallbladder problems, osteoarthritis and some cancers.

Eating too many calories from any source will make you gain weight, whether the calories are from eating fats or carbohydrates.

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