It is a low-carbohydrate, or ketogenic diet, characterised by initial rapid weight loss, usually due to water loss. Drastically reducing the amount of carbohydrate intake causes liver and muscle glycogen loss, which has a strong but temporary diuretic effect. Long-term weight loss occurs because with a low amount of carbohydrate intake, the body burns stored fat for energy. The four-step diet starts with a two-week induction program designed to rebalance an individual's metabolism. Unlimited amounts of fat and protein are allowed but carbohydrate intake is restricted to 15-20 grams per day. Foods allowed include butter, oil, meat, poultry, fish, eggs, cheese, and cream. The daily amount of carbohydrates allowed equals about three cups of salad vegetables, such as lettuce, cucumbers, and celery. The second stage is for ongoing weight loss. It allows 15-40 grams of carbohydrates a day. When the individual is about 10 pounds from their desired weight, they begin the pre-maintenance phase. This gradually adds one to three servings a week of high carbohydrate foods, such as a piece of fruit or slice of whole-wheat bread. When the desired weight is reached, the maintenance stage begins. It allows 40-60 grams of carbohydrates per day.
Opinions of the diet seem to be mixed. There have not been any long term significant studies on the diet. However a number of leading medical health organisations have opposed the diet. This is due to the diet lacking in some vitamins and nutrients, and because it is high in fat. Complications that are also associated with the diet include ketosis (an abnormal increase in ketones in the body, usually found in people with uncontrollable diabetes), dehydration, electrolyte loss, calcium depletion, weakness, nausea, and kidney problems. People with diabetes taking insulin are at risk of becoming hypoglycaemic if they do not eat appropriate carbohydrates. Also, persons who exercise regularly may experience low energy levels and muscle fatigue from low carbohydrate intake.
