The Ketogenic, Atkins, and South Beach diets. These diets are all examples of the trendy low-carbohydrate, high-protein eating plans that claim you’ll lose lots of weight in little time. If you are eating less than 20 grams of carbohydrate a day, you’re following a ketogenic diet. Carbs are the body’s preferred fuel, so if you aren’t eating enough, your body will create an alternative energy source called ketones. The goal of an extremely low-carb diet is to get your body into this state, called ketosis, which is thought to speed weight loss.

Ketosis Risks

People on ketogenic diets can lose weight, at least in the short term, although scientists aren’t entirely sure why. It’s thought that production of ketones may help control hunger or improve the breakdown of fat. But there are risks and side effects involved in losing weight this way. Ketones are meant to be an emergency back-up system for your body, not a long-term energy source. They increase the body’s acidity, which can lead to low blood phosphate levels, decreased brain function, and increased risk for osteoporosis and kidney stones. People on ketogenic diets report higher rates of headaches, bad breath, constipation, diarrhea, general weakness, rash, insomnia, and back pain.

And losing weight isn’t the same thing as gaining health. Cutting carbs from your diet means cutting out (or drastically cutting back on) proven health-promoting foods, like whole grains, fruits, and vegetables, and all of their vitamins, minerals, fiber, antioxidants and phytochemicals. Replacing those carbs on your plate means loading up on protein and fats, so low-carb diets often cause increased consumption of less-healthful red meats and saturated fats.

Other, more balanced, dietary patterns can be just as effective. A 2006 study found that both a ketogenic diet and a low-fat, reduced-carbohydrate diet reduced weight and insulin resistance (a precursor to diabetes), but participants on the ketogenic diet suffered from metabolic and emotional side-effects, while the other group did not. Another study found that severely obese adolescents were able to safely lose weight on a medically-supervised 13-week ketogenic diet, but they lost just as much on a low-fat diet. And studies show many people on ketogenic diets begin to gain the lost weight back within a year.

The Bottom Line

Carbs are the best way to fuel your body—but choose the right ones. Cutting back on carbs like the added sugars in soft drinks, candy and pastries will cut calories and is great for your overall health. Replacing those carbs with nutrient-rich choices like whole grains, fruits and vegetables will give you the nutrients you need for good health, along with the fuel your body craves to perform at its best.

—Judith Thalheimer, RD, LDN

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