A long-term low carbohydrate, high monounsaturated fat diet, compared to a high carbohydrate, low glycemic index diet, results in more rapid progression of diabetes; i.e. increased fasting glucose and glycated hemoglobin, reduced beta-cell function and insulin sensitivity and increased free fatty acids. The deleterious effects of a high carbohydrate diet on plasma lipids are only temporary and do not persist beyond 6 months. A long-term high carbohydrate, low glycemic index diet, compared to a high carbohydrate, high glycemic index diet, improves glycemic control and beta-cell function