High-protein low-carbohydrate diets have become popular again. They include the Zone, Dr. Atkins, Protein Power, Sugar Busters, and Dr. Stillman. As an example, the Atkins diet has a four-phase program:

 
• For the first two weeks individuals consume no more than 20 grams of carbohydrates a day (no fruit, bread, grains, starchy vegetables, or dairy products other than cheese, cream or butter.) This phase is not suitable for children, pregnant women, or anyone with kidney disease. They eat pure protein and fats. (People who choose this diet should, in any case, prefer fish or soy products to meat as protein sources. They should also select monounsaturated fats (as in olive oil) over other fat sources.)  
• After the first phase, individuals continue to lose weight while they increase carbohydrate levels by five grams each week.  
• When individuals get close to their weight goal, they add another 10 grams of carbohydrates per week as long as they do not begin to gain weight. Weight loss is very slow at this time, but the individual is now getting used to maintenance.  
• Lifetime maintenance is usually between 40 and 100 grams of carbohydrates a week.

High-protein diets can be very effective in producing short-term weight loss, but their long-term effects on health are in question. Centers that promote this approach argue that heart problems from obesity are due to insulin disturbances from sugar imbalances. This argument, however, is unproven, and according to many experts is misleading. According to a 2001 report from the American Heart Association, such diets, particularly the Atkin’s diet, are often high in unhealthy fats (although some are emphasizing more healthful oils). They also restrict healthful complex carbohydrates that are known to protect against serious diseases, including heart problems and cancer. A 2002 study suggested that such diets during pregnancy may increase the risk for high blood pressure in the offspring. There are no long-term studies on the safety of these approaches and people who continue them may be at risk for future heart, kidney, bone and liver abnormalities. One byproduct of this diet is the release of substances called ketones, which can cause nausea, lightheadedness, and bad breath.