Abstract and Introduction
Abstract
Dietary modification is considered a cornerstone in the management of diabetes superimposed upon which are pharmacological therapies as required. The value of hypocaloric diets in reducing and eliminating glycosuria was extolled in the pre-insulin era. A common feature of the nutrient balance of these diets was restriction in the availability of carbohydrate. Herein we review the use of diet as therapy in the past and discuss the rationale for hypocaloric dietary management of type 2 diabetes in the 21 century, drawing comparisons with bariatric surgery and considering why weight loss is particularly difficult for overweight and obese individuals with type 2 diabetes.
Introduction
'What goes around comes around', especially for the dietary management of diabetes. The classic studies of Bob Henry and Rena Wing distinguished the important differences between energy deprivation and weight loss in the glycaemic management of overweight and obese type 2 diabetes. Dietary restriction produces immediate reductions in hyperglycaemia, and VLCDs, typically <800 kcal/day, often reinstate near-normal glycaemia within a matter of days. The ongoing control of glycaemia shows only very modest further improvement thereafter despite protracted continuing loss of weight, but the hyperglycaemia quickly re-appears if energy consumption is raised. The rapid benefits of a VLCD include marked improvements of insulin sensitivity and the insulin response to feeding. Excessive hepatic triglyceride deposits also regress, and after an initial increase in circulating fatty acids the lipid profile is much improved. Within reason, fewer calories produce greater benefits and these are largely independent of the extent of weight loss while there is dietary adherence. Whether there is an optimum dietary composition remains unestablished and controversial, but the totality of evidence suggests that the extent of caloric deprivation is the main driver of benefit. The greater difficulty to achieve weight loss in overweight and obese type 2 diabetes than in non-diabetes is likely due in part to the reduced glycosuria in the diabetic individuals, and possibly improved nutrient extraction coupled with the improved anabolic effect of insulin. Additionally dietary restriction and weight loss might produce a greater improvement in metabolic efficiency with a greater reduction of basal metabolic rate in the slimmers with diabetes.