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The Basics About Carbohydrates

The three calorie-providing components of foods are carbohydrates, protein, and fat. Carbohydrates are found in an immense variety of foods. Which of these, for example, are rich sources of carbs: orange juice, table sugar, nonfat milk, pears, strawberries, whole-wheat bread, apple pie, popcorn, biscuits, green peas, muffin, honey, sweet potatoes? If you chose all of these foods, you're right. Carbohydrates (the word means carbon dioxide combined with water) include all the sugars, starches, and fiber we eat. Carbs (except for fiber) are transformed by the body into blood sugar (mostly glucose), the body's basic fuel.

Carbohydrates are the main energy source for the body, and they're the main source of calories in virtually every diet worldwide. They supply 4 calories per gram, the same as protein. Fat has more than twice as many calories (9 per gram)—one reason for its bad reputation. Fiber, however, has no calories, because it isn't absorbed by the body.

Since most carbohydrates are broken down into glucose, why does it matter which carbohydrates you consume? Why is the energy in a teaspoonful of sugar any better or worse than the equivalent amount of carbs in lima beans or whole-wheat bread or, for that matter, in a chocolate bar?

Not so simple, not so complex

Most carbohydrates come from plant-based foods—fruits, vegetables, grains, and legumes (beans, peas, and lentils). Dairy products are the only animal-derived foods with lots of carbs. There are two general types of carbohydrates:

Simple carbohydrates are sugars—glucose and fructose from fruits and some vegetables, lactose from milk, sucrose from cane or beet sugar, and others. Table sugar is pure sucrose. Much of the simple carbs we eat are sugars added to processed foods such as sodas, cookies, etc. These added sugars are the main reason why sugar now accounts for 16% of all calories consumed by Americans; 20 years ago, it supplied 11%. Soda alone supplies about one-third of this added sugar.

Complex carbohydrates, which are chains of simple sugars, consist primarily of starches as well as the fiber that occurs in all plant foods. Starch is the storage form of carbohydrates in plants. Foods rich in complex carbs include grains and grain products (such as bread and pasta), beans, potatoes, corn, and some other vegetables.

Are complex carbs preferable to sugars?

Usually, but not always. Many foods high in sugar (especially sucrose and other added sugars) supply "empty calories"—that is, they have few nutrients but lots of calories. By contrast, the calories in foods rich in complex carbs usually bring many nutritional extras with them. It depends on the food. Dairy products and fruit contain sugars, but are important parts of a healthy diet because of the other nutrients they contain.

Some foods rich in complex carbs are better than others. White bread and french fries contain complex carbs, for instance, but you can make better choices. Whole grains (such as oats, whole wheat, brown rice) are more nutritious than refined grains, since they retain the bran and the germ, which are rich in vitamins, minerals, fiber, and beneficial phytochemicals. Whole grains are digested more slowly, and thus have a more modest effect on blood sugar than refined carbs or sugars (see below). The same is true of vegetables and beans. The fiber in these foods has many health benefits. In particular, soluble fiber (found in oats, barley, and beans) may help lower LDL ("bad") cholesterol, triglycerides, and blood pressure. In fact, people whose diet is rich in whole grains and other high-fiber foods tend to have a lower risk of heart disease, diabetes, and some cancers.

Carb bottom line

The USDA's food pyramid is a good, practical place to start when choosing your high-carb foods. It shows 6 to 11 daily servings of grains, 2 to 4 servings of fruit, 3 to 5 servings of vegetables, and 2 to 3 servings of dairy products (along with small amounts of meat, poultry, or fish). The more calories you consume each day, the more servings you should consume in each category. Servings are small: just one slice of bread or a medium piece of fruit; half a cup of cooked rice, pasta, beans, or vegetables; a cup of raw leafy vegetables; or 3/4 cup of juice. A large apple or banana, a cup of broccoli, or a medium-size salad each counts as two servings.

Such a semi-vegetarian diet will derive more than half its calories from carbs. But be choosy about what kinds of carbs you pick—especially with those 6 to 11 grains. You should include as many whole grains as you can (at least 3 servings a day), according to the government's new dietary guidelines. Limit your intake of highly refined, low-fiber grain products such as white bread. It's much better to get simple carbs (sugars) from fruit, milk, and juice than from cake, cookies (even if low-fat), or soda. There's nothing wrong with small amounts of foods and beverages high in added sugar, but many Americans eat too much of them, adding lots of calories, leaving little room for more nutritious foods, and increasing the risk of chronic disease.

The glycemic index

Various high-carbohydrate foods have different effects on blood sugar. This effect is measured by the "glycemic index," which is mentioned in many of today's diet books. The index indicates how fast a food is digested into glucose and absorbed, and thus how much it causes blood glucose to rise. Some studies suggest that a diet rich in foods high on the glycemic index (meaning they have a strong effect on blood sugar) increases the risk of diabetes, at least in those pre-disposed to it, and lowers HDL ("good") cholesterol.

The index doesn't merely reflect whether the carbohydrates in a food are simple or complex. Many factors come into play, including the amount of fiber and fat in the food, how refined the ingredients are, and whether the food was cooked. Table sugar and honey are high on the glycemic index. But so are raisins, corn, potatoes, carrots, watermelon, doughnuts, white bread, instant rice, and most breakfast cereals. Apples, peaches, and ice cream, as well as most beans, grapefruit, and peanuts, are low on the index. Pasta is in the middle.

The glycemic index has little practical use, however. You shouldn't try to build your diet around it, as some well-known diet doctors (including Dr. Atkins) advise. The main problem: it deals with single foods eaten by themselves. Potatoes may be high on the index, but when eaten as part of a meal, they have much less of an effect on blood sugar. There is no reason to avoid foods high on the glycemic index—many are very nutritious. Even people predisposed to diabetes, or with the disease, can eat these foods in moderation.

Sweet Nothings: Carb Myths

Myth: Carbohydrates, especially sugars, are the leading cause of obesity.

Fact: Eating more calories than you burn causes weight gain—it's that simple. It doesn't matter where those calories come from, as far as weight is concerned. Many obese people get into trouble with excessive amounts of fat, not sugar or starch. In fact, many "sweets" (cakes, ice cream, cookies) actually get most of their calories from fat, not sugar. There's no evidence that eating carbs stimulates appetite or leads to more or easier fat storage and weight gain, as some carb-bashers claim.

Myth: Only refined sugar causes cavities.

Fact: Refined sugar remains the leading dietary cause of tooth decay, but sugars such as fructose in fruit and lactose in milk also promote decay, as do some foods high in fermentable carbohydrates, such as bread and rice. The most important factor: how sticky the food is, since the longer the food remains on the teeth, the more damage is done.

Myth: Sugar makes children hyperactive.

Fact: Though for years parents have been blaming a high sugar intake for their children's uncontrollable behavior, studies have found no evidence for this.

Myth: Sugar in fruit is good, sugar in candy is bad.

Fact: The sugar in most fruit is primarily fructose, which has few, if any, advantages over sucrose (the sugar in candy). So it doesn't matter, for instance, if your jam is sweetened with "sugar" or "fruit juice sweetener."

Myth: Honey and brown sugar are more healthful than table sugar (sucrose).

Fact: Neither offers significant nutritional advantages.

Source: 98
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