Version July 2025
ANSWER —
Correct.
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." But the South Beach Diet is not one diet but a series of three diets or phases [1,2]. Phase 1 is a very low-carbohydrate diet initially 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 Phase 1, 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 a 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 secretagogue, 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 secretagogues. In the absence of adjustments in dose of insulin or an insulin secretagogue, 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-controlled 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 [3] (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 [4,5]. The long-term impact on cardiovascular risk factors and outcomes is not known. (See "Obesity in adults: Dietary therapy", section on 'Low-carbohydrate diets'.)
While one should not recommend the South Beach Diet in its entirety to a patient with type 2 (or type 1) diabetes, because of the inclusion of Phase 1, Phase 2 of the South Beach Diet is (generally speaking) a reasonable diet, one that is consistent with the current American Diabetes Association (ADA) guidelines. In a patient who is motivated to follow it, the South Beach Diet can be used under medical and nutritional supervision with omission of Phase 1.
Patients often lack motivation and perseverance to alter their nutritional pattern, a source of frustration to those who care for them. Also, a patient's decision to alter his or her lifestyle is often related to social circumstances, as in the patient under consideration, who is motivated to make changes in response to his daughter's encouragement. This patient, who had paid little attention to nutrition until recently, is now motivated to follow an appropriate nutritional regimen to improve his glycemic management and to lose weight. Unfortunately, he changed his diet without medical supervision, with adverse consequences. Nevertheless, the patient remains motivated and seeks your advice. This is the time to renew your efforts to achieve an improved lifestyle and to take into account the source of his motivation. (See "Initial management of hyperglycemia in adults with type 2 diabetes mellitus", section on 'Intensive lifestyle modification'.)
As with any diet that limits or changes carbohydrate content, a fall in the required dose of insulin or an insulin secretagogue is to be expected. Some reduction in the doses of these agents should be advised. Of course, any such recommendation is an approximation. Further adjustments should be made in a timely manner in response to the patient's self-monitoring and glycated hemoglobin (A1C) values.
The patient agrees to follow your advice. He also asks your opinion about eating fish. He loves fish, but his daughter has heard about mercury contamination in fish, and he does not know what to do. What do you advise?
●You advise him to eat fish at least twice a week and to enjoy it. (See "Interactive diabetes case 18: A 61-year-old patient with type 2 diabetes and a recent change in diet (medical nutrition therapy) – B1".)
●You advise him to avoid fish because of mercury contamination. (See "Interactive diabetes case 18: A 61-year-old patient with type 2 diabetes and a recent change in diet (medical nutrition therapy) – B2".)
Please note that answer A5 is also correct. (See "Interactive diabetes case 18: A 61-year-old patient with type 2 diabetes and a recent change in diet (medical nutrition therapy) – A5".)
