Mayo Clinic

Low-Carbohydrate Diets: Are They Safe and Effective?
Mayo Foundation for Medical Education and Research

Mayo Clinic is a charitable, not-for-profit organization based in Rochester, Minn. comprising of an integrated multi-specialty clinic and two hospitals, staffed by more than 1,500 physicians.

Americans spend billions of dollars yearly on weight-loss programs and products, looking for the magic cure to help them shed pounds quickly and painlessly. Anyone who has tried to lose weight knows how challenging it can be. This is why many people turn to fad diets.

Fad diets have been around for decades. New ones surface regularly, and some older ones fall in and out of favor. One of the more popular diets today is a low-carbohydrate, high-protein diet. Researchers have reported some successful short-term results from restricting carbohydrate intake, findings that have sparked further debate in the medical community about the effectiveness and safety of such diet programs.

Low-carbohydrate diets — such as the Atkins diet, the Zone and the South Beach Diet — have received a lot of attention. With book sales in the millions and pervasive marketing campaigns, many people turn to these diets for help in losing weight. But it’s important to ask yourself the same questions posed by health experts: Do these low-carbohydrate, high-protein diets work? Are they safe?

Low-carbohydrate diets: The theory

The main thrust behind low-carbohydrate diets is that carbohydrates promote insulin production, which leads to weight gain. So, the theory goes, reduce your intake of carbohydrates and you’ll shed extra pounds.

The Atkins diet — one of the more popular low-carbohydrate diets — limits carbohydrates to 20 grams a day initially. By contrast, the National Academy of Sciences’ Institute of Medicine recommends that most adults consume at least 130 grams of carbohydrates each day. The Atkins diet excludes most grains, beans, fruits, breads, rice, potatoes, pastas and starchy vegetables. You can eat generous amounts of beef, pork, chicken, eggs and butter.

How does a low-carbohydrate diet actually work? By lowering your daily intake of carbohydrates, your body burns its stored carbohydrates (glycogen) for energy. When your body burns glycogen, water is released, and you lose weight.

Your body also starts burning some fat. Burning fat without carbohydrates creates byproducts called ketones that build up in your bloodstream (ketosis). Your kidneys remove the ketones from your bloodstream and eliminate them from your body through urine. Ketones suppress appetite, but they may also cause fatigue and nausea. Proponents of the Atkins diet claim that “benign dietary ketosis” is a safe, natural condition necessary for weight loss. Finally, if the total calorie intake on a low-carbohydrate diet is low enough, this leads to loss of muscle tissue, which also shows up on the scale as weight loss.

The traditional lower-fat, calorie-controlled diet

Most medical experts recommend a diet that’s low in saturated fat and calories, while being moderate to high in complex carbohydrates. The Dietary Guidelines for Americans, developed by the U.S. Department of Agriculture (USDA) and the Department of Health and Human Services (HHS), outlines several guidelines for better health:

  • Eat a variety of foods to get the energy, protein, vitamins, minerals and fiber you need for good health.

  • Balance the food you eat with physical activity — maintain or improve your weight to reduce your chances of having high blood pressure, heart disease, a stroke, certain cancers and diabetes.

  • Select a diet low in sugar. A diet high in sugar has too many calories and too few nutrients for most people.

  • Choose a diet low in salt to help reduce your risk of high blood pressure.

  • Eat plenty of grain products, vegetables and fruits to provide you with needed vitamins, minerals, fiber and complex carbohydrates, and to help lower your intake of fat.

  • Choose a diet low in fat, saturated fat and cholesterol to reduce your risk of heart attack and certain types of cancer, and to help you maintain a healthy weight.

  • Drink alcohol in moderation. Alcohol supplies calories, but little or no nutrients.

Low-carbohydrate diet: The upside

People, especially meat lovers, like eating the food on the low-carbohydrate diet — at least for a while. They also report that eating these foods suppresses their appetite. A study published in the May 2003 issue of the New England Journal of Medicine compared the Atkins diet with a low-fat, low-calorie diet. Researchers found that both diets resulted in weight loss. The study also found that those people who followed the Atkins diet:

  • Lost more weight, faster. This advantage was apparent for the first six months. But at one year, the difference between the Atkins group and the low-fat, low-calorie group wasn’t statistically significant.

  • Improved high-density lipoprotein (HDL) cholesterol — the “good” cholesterol — and triglyceride levels. These results surprised some opponents of this diet who had maintained that a high-fat diet would negatively affect cholesterol levels.

Low-carbohydrate diet: The downside

These same researchers found that after a year, there was no significant difference in weight loss between the low-carbohydrate diet and a standard low-calorie diet. Also, sticking to a low-carbohydrate diet doesn’t appear to be any easier than following other weight-loss plans. People on the Atkins diet dropped out at a similar rate as those following the low-fat diet. If dieters aren’t getting the results they want — anticipated weight loss — they drop out. This suggests that the low-carbohydrate diet, like so many diets, is no easier to stick to long term. And although you may initially prefer eating the foods included in the low-carbohydrate diet plan, food choices are actually more limited and perhaps less appealing over time.

Proponents of the Atkins diet claim that ketosis helps burn fat. However, researchers found no correlation between ketosis and weight loss in the Atkins diet. Prolonged ketosis may deplete mineral stores in the bones, causing them to become porous and brittle.

Research hasn’t yet determined the long-term effectiveness or risks of the low-carbohydrate diet. And there’s concern in the medical community about the long-term effects of these diets on a dieter’s health, especially on the heart. It’s well documented that foods promoted in the low-carbohydrate diets — for example, foods high in saturated fat such as meat, butter or cream — have been shown to increase your risk of heart disease and some types of cancer. And foods restricted on these diets — for example, whole grains, vegetables and fruits — have vitamins, minerals and other nutrients that can help reduce your risk of diabetes, heart disease, cancer and other health conditions.

Bottom line: Are they safe and effective?

Do these diets work? Low-carbohydrate diets do work in the short run. But their long-term weight-loss results aren’t significantly better than those of standard diets.

Are they safe? It’s impossible to say because little is known about their long-term effects on heart disease, cancer and other health conditions.

Bottom line: Be wary of diets that promise a quick fix or that sound too good to be true. Aim for a long-term plan — one that offers you a lifetime of tried-and-tested health strategies. Though traditional recommendations for weight management — eating a variety of vegetables, fruits and grains, and being physically active daily — may produce slower results, they’re the proven path to improved health and lasting weight loss.