Version July 2025
ANSWER —
Incorrect.
The South Beach Diet is a popular diet and has many good features, including the emphasis on eating "the right carbs and the right fats" [1]. But the South Beach Diet is not one diet but a series of three diets or phases. Phase 1 is a very low-carbohydrate diet recommended for two weeks to achieve rapid weight loss. It is a variant on the many very low-carbohydrate or ketogenic diets that have been advocated in the past but without measurement of ketones. In it, the patient eliminates carbohydrates, including bread, rice, potatoes, pasta, baked goods, and fruit. The ability of patients without diabetes to tolerate this diet after the first one to two days without craving foods may reflect the ketosis that develops during extreme carbohydrate restriction.
Phase 2 involves the reintroduction of certain "healthy" carbohydrates that were excluded in the earlier phase, such as fruit, whole-grain bread, whole-grain rice, whole-wheat pasta, and sweet potatoes. The goal of this phase is to achieve gradual weight loss of 1 to 2 pounds per week. Readers are advised to follow this diet until the target weight is achieved, a process that may last for many months or longer. Readers are also advised to revert to Phase 1 on those occasions when they have failed to adhere to Phase 2 and have regained some weight. Phase 3, to begin when the "ideal" weight is achieved, involves the long-term adoption of a healthy lifestyle. Here again, the reader is advised to return to Phase 1 for one or two weeks intermittently when "you overindulge a little."
The Phase 1 diet should not be used in patients on insulin or an insulin secretogogue, as it is difficult to predict its effect on the required dose of these agents. The sudden and marked reductions in carbohydrate intake will result in corresponding decreases in insulin requirement or dose requirement for insulin secretogogues. In the absence of adjustments in dose of insulin or an insulin secretogogue (or possibly even with adjustments), major changes in glycemia will often occur. Hypoglycemic reactions (sometimes severe) may occur, as in the patient under consideration. By the time appropriate adjustments are made, the doses will have to be changed again when the patient moves to the Phase 2 diet. The conversion from Phase 1 to Phase 2, or from Phase 2 to Phase 3, will be accompanied by hyperglycemia in a previously well-managed patient and will usually necessitate an increase in the doses of insulin or other diabetes medications.
In general, the value of a very low-carbohydrate or ketogenic diet is questionable. When used for a brief period, as such diets have been in the past, patients almost invariably regain the weight that has been lost on the diet when they return to the previous diet. Very low-carbohydrate diets are not recommended for long-term use [2] (see "Medical nutrition therapy for type 2 diabetes mellitus"). The long-term effects of very low-carbohydrate or ketogenic diets are not known. Although they may produce short-term weight loss, the long-term effect on weight loss is similar to that from low-fat diets [3,4]. The long-term impact on cardiovascular risk factors and outcomes is not known. Also, foods that contain carbohydrate are important sources of energy, fiber, vitamins, and minerals and are important in diet palatability [2]. (See "Obesity in adults: Dietary therapy", section on 'Low-carbohydrate diets'.)
The short-term use of a very low-carbohydrate diet in adults without diabetes as part of a long-term dietary program such as the South Beach Diet has certain advantages, in particular the enhanced motivation that often occurs when short-term weight loss is achieved. However, in patients treated with insulin or an insulin secretagogue, the risks of altered glycemic management and especially of hypoglycemia outweigh the putative benefits. In a patient with type 2 diabetes who is not on these medications, the use of a ketogenic diet is also unwise. In a patient without diabetes, ketosis is a measure of the lipolysis and ketogenesis that occur physiologically in response to a markedly reduced carbohydrate intake and decreased endogenous insulin secretion. In a patient with diabetes, ketosis means inadequate diabetes management until proven otherwise.
Return to the beginning to try again. (See "Interactive diabetes case 18: A 61-year-old patient with type 2 diabetes and a recent change in diet (medical nutrition therapy)".)
