Carbohydrates are an essential part of a healthy diet. They’re the body’s fuel of choice: Glucose—the body’s gasoline—is more readily available from carbohydrates than protein or fat.

To lose weight:  Use carbs. Yes, eat more! "People who eat complex carbohydrate–rich diets tend to be leaner than those on other diets, probably because they feel fuller after eating and are consuming fewer high-calorie, fatty foods," says registered dietitian Marsha Hudnall, nutrition director at Green Mountain at Fox Run, a weight-management community in Ludlow, VT. "Variety creates satiety," she says.

But what about the impressive weight-loss claims for protein diets? "Protein diets appear to be easy to follow, and you lose weight quickly because you’ve eliminated two whole food groups (starches and fruits). And there's only so much steak you can eat," says Johanna Burani, a registered dietitian in Mendham, NJ. "But because the diet is so restrictive, people get sick of it. And when they go off a protein diet, the body stops burning fats for energy, which can cause almost immediate weight gain. So it’s not a real fix for a weight problem."

"Researchers rank carbohydrates from 0 to 100 based on how fast they are converted to glucose and enter the bloodstream, a rating called the Glycemic Index (GI)," says Burani. The higher the GI of a carbohydrate, the faster it is broken down in the body and the more quickly and dramatically it raises your blood glucose level. Pure glucose is 100, a baked potato can be as high as 93, and nonfat, plain yogurt is 14. (See box, "Foods to Fuel You" for rankings of commonly consumed carbohydrates.)

To lose weight: Expand your definition of carbohydrate. You should get 55 to 60 percent of your total calories from carbohydrates, and we’re talking fruits and vegetables here, not just the starchy bread/rice/pasta options at the bottom of the food pyramid. Whole grains, fruits, and vegetables contain lots of fiber, so they are digested slowly, giving them a lower GI index. When you do choose bread/rice/pasta, make sure you pick fiber-rich whole grain or cracked wheat breads, brown or Basmati rice, and semolina pastas made from durum wheat.

Don’t overcook carbs: Spaghetti cooked al dente has a GI of only 41. The light cooking maintains the layers around the starch at the core of the pasta. Digestive enzymes must gnaw through these multiple layers to get to the starch. If pasta is cooked until it is very soft and loaded with water, however, these layers will degrade and the food will have a higher index (close to 100), says Richard Podell, M.D., author of The G-Index Diet. If you crave potatoes, steam them. Mashing potatoes creates more surface area for digestive enzymes to attack, increasing the GI rating.

"The body may prompt cravings for carbohydrates because they’re the most direct route to fuel," says Hudnall.

 To lose weight: If you’re experiencing cravings after eating certain carbohydrates, it may be because you’re consuming too many high-GI, fast-release foods that have little staying power. Add in some low-GI foods at every meal and you’ll feel fuller longer, suggests Burani. Eat a baked potato with beans; add greens, corn, tomatoes, and/or cabbage to rice and pasta dishes. "The mix of high- and low-GI foods will even out your blood sugar surges," she says.

To lose weight: Eat more low-GI foods and you’ll burn up to 200 more calories per day. A steady intake of low-GI carbs keeps blood sugar even and slows down the release of insulin, a hormone whose main job is to deliver the sugar into muscle cells for later use as fuel. Under normal conditions, when insulin is low in the bloodstream, the body burns more fat. In contrast, when there is a high level of insulin circulating in the blood, the body is programmed to store fat, says Burani. The higher your blood sugar rises after a meal, the more insulin will be released and the more storage of fat will subsequently occur.

Carbohydrate-rich foods also tell your brain you’re full faster than do fat-laden foods. And that leads to another advantage of eating low-GI carbohydrates, says Burani: They contain lots of fiber, which slows down the digestion process and makes you feel fuller. They also hold a lot of water—another filling factor—and you need to chew them a lot, which can be more satisfying.

What’s more, most recent studies show that eating at night—whether it’s carbs or not—leads to no more weight gain than day eating. Again, it’s your total calorie count for the day that’s important.

To lose weight: If you tend to get hungry at night, try spreading your calories out over the course of the whole day, with an emphasis on low-GI carbohydrates that will keep your blood glucose level and naturally keep hunger at bay. "Women tend to be really good at restricting their calories during the day, but they end up so ravenous they devour everything in sight at night," Berning says. Eat small meals every four to five hours during the day to keep your blood sugar on an even keel and your energy level up. The meals should be primarily composed of carbs (55 to 60 percent), with a smattering of protein (10 to 15 percent) and fat (30 percent or less).

Weight Loss Aids: What works, what doesn't, and what's downright dangerous

Loss weight fast—and naturally...Boost your metabolism...Pare inches off your waist without dieting or exercise...Cruise the weight-loss section in any drugstore or health-food shop and you'll find yourself surrounded by various products promising to burn, trap, and zap your fat. Some of these supplements will help you lose pounds; others are just a waste of money. How to tell the difference? Read on.

The newest development in meal-replacement drinks is Satietrol, a pre-meal beverage. In one recent study, women who drank Satietrol while on a six-week calorie-restricted diet lost an average of nine pounds. They reported feeling full up to three and a half hours after having the drink and also ate less at the next meal. The beverage contains potato fibers and works because it activates the body's natural appetite-control protein, called  cholecystokinin. This protein signals you to stop eating when you're full and slows the movement of food from the stomach, keeping you satisfied longer. The beverage, which you drink 15 minutes before eating a meal, contains 80 calories and is available at GNC stores for a little more than a dollar (rough the same price as a Slim-Fast shake).

Conjugated linoleic acid. Sold through health-food stores and drugstores as a dietary supplement, CLA appears to help you zap fat. A fatty acid derived from sunflower oil and found in dairy products and red meat, CLA both blocks fat storage and prompts cells to dump the fat they're already holding, says Michael Pariza, Ph.D., director of the Food Research Institute at the University of Wisconsin, Madison, and the scientist who first discovered CLA.

Research on CLA has been promising: "Studies show that over four to 12 weeks of use, you can lose up to four pounds," says Delbert Dorscheid, an assistant professor of medicine at the University of British Columbia in Vancouver. "It also helps you gain muscle, to help trim inches off fatty areas—particularly the abdomen and upper arms—especially if you exercise." Since CLA makes you build muscle as well as lose fat, you won't necessarily see big changes on the scale, but your clothes will fit better. CLA may even help prevent weight gain, since increased muscle mass makes you a more efficient fat burner, says Pariza.

At the very least, CLA may simply make dieting a more pleasant experience: In a six-month study conducted by Pariza, obese people who took CLA while dieting didn't suffer as many weight-loss-related adverse effects, such as headache and nausea. (Pariza theorizes that this is because of CLA's effects on the immune system.) Only two brands available in the United States—Tonalin and Clarinol—have  have been well tested for safety and effectiveness. A month's supply costs $30, but don't buy in bulk: Researchers say that for the time being, they only know it's safe to take CLA in doses of one gram three times a day for up to six months.

Chitosan. An ingredient in many so-called weight-loss aids, this dietary fiber, derived from shellfish, is purported to act as a fat blocker. But several studies dispute this claim: "We investigated how much fat subjects excreted before and after taking a chitosan product, says Judith S. Stern of the University of California, Davis. "We found no increase in fat excretion after they took the supplement , so it wasn't blocking fat absorption." Another study, which compared chitosan to the prescription weight -loss drug Xenical, also found that chitosan doesn't trap fat. Don't bother taking it, since there's little proof it works and it may actually be bad for you: According to some research, chitosan may inhibit the absorption of vitamins A, D, and K.

Pyruvate . This compound, found in many "fat-burning supplements" sold in health-food stores, may work in large doses. Some evidence has suggested that taking 22 to 28 grams of pyruvate a day can mildly assist in fat loss.

Nevertheless, according to Sukula, smaller doses may not work. The studies that have shown smaller amounts of pyruvate may be effective used supplements that were loaded with other compounds, including herbal diuretics. "We don't know if pyruvate was the active ingredient that caused weight loss," Sukula says. Other research has found that it may even work against your weight-loss goals: In one study at Appalachian State University in Boone, North Carolina, subjects who took pyruvate actually lost less weight than control subjects who took placebos.