There is little doubt that weight loss in response to calorie-restricted diets will improve both glycaemic control and dyslipidaemia in patients with Type 2 diabetes (6-11). However, there are two questions concerning this issue that deserve some attention. In the first place, do variations in the relative proportion of macronutrients have any effect on the ability of patients with Type 2 diabetes to lose weight? Three relevant papers bearing on this issue have been published in the last few years, comparing weight loss in response to calorie-restricted diets, varying only in terms of relative proportions of CHO and fat. The results showed that weight loss was identical when dietary CHO varied from 10% to 70% of daily calories, with proportionate changes in fat content (9-11). Since the longest of these studies only lasted for 12 weeks (8), it could be argued that differences in rate of weight loss might have emerged if the patients had been followed for longer. On the other hand, there is no evidence that relatively large variations in the relative amounts of dietary CHO and fat present in energy-restricted diets have a discernible effect on the ability of patients with Type 2 diabetes to lose weight.
Variations in relative amounts of dietary CHO and fat did not prevent the improvement in glycaemic control associated with weight loss, but in two of the studies (9,10) the fall in plasma glucose concentration was significantly greater on a higher monounsaturated fat (MUF)-lower CHO diet. Plasma triglyceride
(TG) and high-density lipoprotein (HDL) cholesterol concentrations fell with weight loss, irrespective of macronutrient content, but the decrement in TG concentration was greater, and the fall in HDL cholesterol attenuated, in response to calorie-restricted diets relatively high in MUFA and low in CHO. Low-density lipoprotein (LDL) cholesterol concentration decreased when either MUFA or CHO replaced saturated fat (SF) in the diet, but the improvement in LDL cholesterol concentration did not take place if dietary intake of SF was not decreased. Finally, improvement in all of these variables in response to a diet relatively high in MUFA and lower in CHO persisted several weeks after a period of weight maintenance with the test diets.
In summary, weight loss in overweight patients with Type 2 diabetes is of substantial clinical benefit, and is almost certainly the most powerful lifestyle modification to improve clinical outcome in this population. Although variations in relative proportion of dietary fat and CHO in energy-restricted diets do not seem to affect the amount of weight loss, the metabolic benefit associated with weight loss was somewhat greater when the diet was relatively higher in MUFA and lower in CHO.
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