The Lowdown on Low-Carb Diets

Low-carb/high-protein diets—such as Atkins, South Beach, the Zone, and Sugar Busters—are getting a lot of attention these days, as alternatives to the more traditional weight-loss diets that stress carbohydrates and limit fats. But while some studies show people on these diets can lose weight in the short term, questions remain as to whether they can maintain their weight loss and their health over time.

Weight loss is a hot topic, because nearly two-thirds of American adults are overweight and 31 percent are obese, according to the CDC.

Low-carb theory

Atkins and other low-carb/high-fat diets focus on the fact that carbohydrates raise blood sugar and insulin levels in the body. Insulin drives blood sugar into the cells and prevents fat from breaking down in the body; this keeps you from losing weight. Proponents of low-carbohydrate diets take this one step further. They say that if carbohydrates raise blood sugar and insulin levels and cause weight gain, a decrease in carbs will result in lower blood sugar and insulin levels, leading to weight loss. And because you're not eating the carbs, your body breaks down fat to provide needed energy.

The upside

The primary advantage of a low-carb diet is that it eliminates, or severely restricts, refined carbohydrates, such as white bread, pasta, cookies, doughnuts, and soda, which provide empty calories, lack nutrition, and give you a sugar jolt. Your blood triglyceride levels also may decrease.

You lose weight on a low-carb diet because you lose water weight. You eat fewer calories because of the restrictions in the diet, and your appetite decreases. Your appetite decreases because substances called ketones build up in the blood. Ketones are produced when the body burns fat without carbohydrates.

The downside

The major disadvantage of low-carb diets is that research hasn't yet determined their long-term effectiveness, benefits, or risks. Meanwhile, numerous studies have found that foods promoted in most low-carb diets—foods high in saturated fat, such as meat, butter, and most cheeses—increase the risk for heart disease and some types of cancer. Research also has documented that foods restricted on these diets—whole grains, vegetables, and fruits—have vitamins, minerals, and other nutrients that reduce the risk for diabetes, heart disease, cancer, and other health conditions. Long-term exposure to ketones may also reduce the minerals in your bones, leaving them porous and brittle.

According to Caitlin Hosmer, M.S., R.D., L.D.N., a Boston nutrition consultant, low-carb/high-protein diets raise health concerns because they're:

• High in protein, which may increase stress on the kidneys, especially for those prone to kidney problems.

• High in saturated fat and total fat, possibly leading to an increased risk for heart disease.

• Low in complex carbohydrates found in fruits and vegetables, possibly leading to constipation and diminished cancer prevention.

Controversial studies

One small, short-term study published in 2003 in the New England Journal of Medicine (NEJM) followed relatively healthy obese people on the Atkins diet and on a more conventional low-calorie, low-fat, high-carb diet. It found Atkins dieters dropped more pounds more quickly in the first six months of the study. Fifty-nine percent of the subjects completed the year-long study. At the end of one year, there was no significant difference in weight loss between the two groups. Those on the Atkin's diet had a greater decrease in triglyceride levels and greater increases in HDL ("good") cholesterol.

The long-term health effects of the Atkins and other low-carb diets are unknown. As the editors of the NEJM noted, "Longer and larger studies still are needed to determine the long-term safety and efficacy of low-carbohydrate, high-protein, high-fat diets."

A better way

According to some nutrition experts, including Sandra Woodruff, M.S., R.D., L.D.N., author of Secrets of Good-Carb/Low-Carb Living, it's possible to follow a low-carb diet and not increase health risks by making commonsense changes to the diet itself.

"Not all low-carb diets are good, and following a low-carb diet that's heavy on bacon cheeseburgers, cream, and butter and low in vegetables, fruits, and whole grains can jeopardize your long-term health," she says. "But if you combine the best parts of low-carb diets with the best parts of low-fat diets, you can lose weight while reducing your risk for cardiovascular disease, cancer, and kidney problems."

Her suggestions for improving the standard low-carb diet for weight loss and better health:

• Opt for lean protein, such as baked or broiled skinless poultry, seafood, and lean red meat, instead of high-fat meats or deep-fried chicken and fish.

• Choose low-fat dairy products, such as skim milk and low-fat cheese, instead of regular milk and cream.

• Eat plenty of fruits and nonstarchy vegetables, such as salad greens, spinach, celery, peppers, scallions, asparagus, broccoli, and tomatoes. Limit potatoes, corn, and most beans (but not string beans).

• Choose reasonable portions of healthy carbs, such as brown rice, whole-grain bread, and high-fiber cereal, instead of white bread, white rice, doughnuts, cookies, and pastries.

• Use polyunsaturated or monounsaturated fats, such as olive oil, canola oil, trans-fat-free margarine, and low-fat salad dressings, instead of butter, lard, and regular salad dressings. But use them sparingly.

• Be sure meals and snacks include protein and fiber-rich foods. "Including protein and fiber-rich foods that have a lower glycemic level will maintain more stable blood sugar levels and help you feel full and satisfied," Woodruff says.

• Get plenty of exercise. The American Dietetic Association recommends 30 minutes of moderate exercise for adults and 60 minutes for children and teens on most days of the week. Physical activity is an important part of weight management because it burns calories.

"It's important to remember that not one diet plan fits all," Woodruff says. "But making healthful food choices, eating reasonable portions, and being physically active are proven ways to attain and maintain a healthful weight."