Carbohydrates

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Carbohydrates

Nutrition
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What's in Your Food
Carbohydrates
Carbohydrates
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Carbs provide high octane fuel for energy.
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InteliHealth
2009-01-02
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InteliHealth Medical Content
2011-01-02

Reviewed by the Faculty of Harvard Medical School

Carbohydrates

Pasta 1 Carbohydrates are the body's main 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.

Are Sugar Substitutes Safe?

The Food and Drug Administration (FDA) has approved four sugar substitutes: saccharin, aspartame, acesulfame-K and sucralose.

Saccharin (available as Sweet 'n Low) is a noncaloric, indigestible petroleum product that is 300 times sweeter than sugar. In the late 1970s, a study linked saccharin to cancer in laboratory rats, and the product was nearly removed from the market. But the case against the sweetener was dropped when it was disclosed that the rats had consumed saccharin in the equivalent of 800 cans of diet soda a day.

Aspartame (Equal or NutraSweet), a synthetic combination of two amino acids, contains four calories per gram, just like sugar. But aspartame is 200 times sweeter than sugar, so much less is needed. Although the FDA ruled that most people could safely consume the equivalent of 97 packets of aspartame daily, some consumers have complained of headaches and other side effects. Aspartame was originally approved in 1981 for use in powdered drinks and as a tabletop sweetener. In 1996, aspartame was approved for use in all foods and beverages, including products such as syrups, salad dressings and snack foods where prior approval had not been granted. All foods containing aspartame must carry a label warning that people with phenylketonuria (PKU),an inherited inability to metabolize one of the amino acids (phenylalanine) in aspartame, should not eat the product.

Acesulfame-K (Sweet One) is chemically similar to saccharine and 200 times sweeter than sugar. It's found in dry beverage mixes, instant coffee and tea blends, puddings, gelatin mixes and chewing gum. The sweetener's safety was called into question when laboratory rats developed tumors during testing, but the FDA maintains that the tumors were unrelated to the product.

Sucralose (Splenda) is made from sugar cane that is 600 times sweeter than table sugar. About 15 percent of the sucralose taken by mouth is absorbed in the intestines without being broken down. The remainder passes through the body. In the body, sucralose does not act like a carbohydrate. It provides no calories or energy. Studies done so far indicate that it is safe, but sucralose has only been in widespread use in the United States for the past five years.

 

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Last updated September 09, 2013


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