CONTEXT: Carbohydrate-restricted diets have been popular in recent years. The theoretical glycemic impact of these diets, compared with other popular weight-loss diets, has not been reported. OBJECTIVE: To assess the glycemic index (GI) and glycemic load (GL) of 2 popular, carbohydrate-restricted diets (South Beach and Sugar Busters!) and compare them with a low-fat, high-carbohydrate diet (Ornish) and a moderate-fat, moderate-carbohydrate diet (EatRight). DESIGN: All available sample menus provided in the book for each diet were extracted and included in the analyses. GI values for all carbohydrate-containing foods were assigned based on a published list. GL values were determined based on these GI values and recommended serving sizes. MAIN OUTCOME MEASURES: Median daily GI and GL values were calculated for each diet and for each phase of South Beach and each meal pattern of EatRight. RESULTS: The median daily GLs of South Beach and Sugar Busters! (34 and 48, respectively) were less than one half those of Ornish and EatRight (113 and 104, respectively). Adjusting the diets to 1500 kcal attenuated the differences slightly. The median daily GIs of the diets were in a very narrow range (46-53); however, South Beach (46) was significantly lower than Ornish (53). CONCLUSIONS: The GLs of 2 carbohydrate-restricted diets were significantly lower than those of a low-fat, high-carbohydrate diet and a moderate-fat, moderate-carbohydrate diet. The differences were due primarily to lower carbohydrate content rather than to differences in overall GIs of the diets.