Dr. Agatston believes that excess consumption of so-called "bad carbohydrates" creates an "insulin resistance" syndrome—an impairment of the hormone insulin's ability to properly process body fat or sugar. In addition, he believes, along with most doctors, that excess consumption of "bad fats" contributes to an increase in cardiovascular disease.
To prevent these two conditions, Agatston's diet minimizes consumption of bad fats and bad carbs and encourages increased consumption of good fats and good carbs.
The diet has three phases. In all phases of the diet, Dr. Agatston recommends minimizing consumption of bad fats. In Phase I, lasting two weeks, dieters attempt to eliminate insulin resistance by avoiding moderately high- or high-glycemic carbs, such as sugar, candy, bread, potatoes, fruit, cereals, and grains. During Phase I, Dr. Agatston says the body will lose its insulin resistance, and begin to use excess body fat, causing the dieter to lose between 8 and 13 pounds.
After two weeks, Phase II begins. Whole grain foods and fruits are gradually returned to the diet, although in smaller amounts than were likely eaten before beginning the diet, and with a continued emphasis on foods with a low glycemic index. When the dieter reaches the desired weight Phase III begins. In Phase III the diet expands to include three servings of whole grains and three servings of fruit a day.
The diet distinguishes between good and bad carbohydrates, and good and bad fats.
Good carbs are high in fiber or high in good fats, and have a low glycemic index, that is, they are digested and absorbed slowly. Other preferred carbohydrates are those with more nutritional value than the alternatives. For instance, brown rice is allowed in moderation, but white rice is discouraged. When eating any carbohydrates, Dr. Agatston recommends also eating fiber or fat to slow digestion of the carbohydrates.
- Good fats are polyunsaturated and monounsaturated fats, especially those with omega-3 fatty acids. Saturated and trans fats are bad fats.
This diet emphasizes (1) a permanent change in one's way of eating, (2) a variety of foods, and (3) ease and flexibility. Eating whole grains and large amounts of vegetables is encouraged, along with adequate amounts of mono- and polyunsaturated fats, including omega-3 fatty acids, such as are contained in fish. It discourages the eating of overly refined foods (particularly refined flours and sugars), high fat meats, and saturated fats.
The diet does not require counting calories or limiting servings- Agatston suggests you eat until you are satisfied. Dieters are told to eat 6 meals a day - breakfast, lunch, and dinner - and small snacks between each meal.
In 2004, Kraft Foods licensed the South Beach Diet trademark for use on a line of packaged foods that would be designed to meet the requirements of the diet. There is some concern that this will lead to the situation that the Atkins Diet found itself in, with some licensed products allegedly falling outside the scope of the diet.