Dietary recommendations for people with diabetes: Time to reduce the carbohydrate loads

The following guest editorial by by Samy I. McFarlane, MD, MPH (who I just discovered thanks to Dr. Katharine Morrison) is a great read--in addition, the sources cited at the end of the article are immensely valuable.


Recommendations should take account of current evidence for carbohydrate restriction.

by Samy I. McFarlane, MD, MPH

September 2005

Samy I. McFarlane, MD, MPH [photo]
Samy I. McFarlane

The current dietary guidelines for people with diabetes are based on a traditional low-fat/high-carbohydrate strategy with carbohydrate intake ranging between 55% to 70%. These diets have largely failed for people with diabetes as well as for the general population.

In fact, the epidemic of obesity and diabetes in our society over the past three decades has been accompanied by a steady decline in fat consumption and an apparent attempt to adopt the recommended low-fat diet.

According to the USDA Continuing Survey of Food Intakes by Individuals (CSFII), the absolute amount of fat as well as saturated fat consumed has significantly decreased during the obesity epidemic.

From a public health perspective, this represents a failure of low-fat/high-carbohydrate strategies to curb the obesity epidemic or at least to negate the other contributing factors such as sedentary lifestyle.

In people with diabetes, where traditional low-fat diets are recommended, reports by our group and others including national data indicate that only a minority of patients achieve the recommended treatment goals.

For example, in a national survey by our group across several health care delivery systems, 3,678 records of diabetic patients were examined with only one-third of the patients achieving HbA1c of <7% and less than half with LDL-cholesterol of <100 mg/dL. In this cohort of diabetic patients, 85% were either overweight or obese, with only 15% having a BMI <25.

These data, from 2002, are consistent with data from the Third National Health and Nutrition Examination Survey (NHANES III, conducted 1988-1994) and NHANES 1999-2000. Collectively, these data show a consistent pattern of overwhelming obesity and poor control of glycemia and dyslipidemia in the diabetic population despite decades of low-fat recommendations.

These observations point to the need for alternative dietary approaches. Among these approaches, lowering the carbohydrate content of the diabetic patients needs to be strongly considered given the current evidence for its effectiveness.

Carbohydrate intake and glycemic control

Several epidemiological studies including the Nurses Health Study and the Health Professional Follow-Up Study have linked dietary carbohydrate intake (measured as glycemic load) with the risk of type 2 diabetes and CVD.

Prospective cohort studies have also linked carbohydrates with the development of diabetes. We have summarized evidence from clinical and metabolic studies demonstrating worsening of glycemic control and dyslipidemia in diabetic patients with a high-carbohydrate diet while showing how carbohydrate restriction may reverse these serious metabolic abnormalities.

The beneficial effects of lowering the carbohydrate content for patients with diabetes were, in fact, acknowledged in the current guidelines of 2005, but were quickly dismissed on the basis of “concern that increased fat intake in ad libitum diets may promote weight gain.”

This concern, however, has not been substantiated, and at least two studies show that low-carbohydrate diets are not associated with increase in dietary intake of proteins or fats presumably due to effect of these diets on satiety.

Also, despite nominal ad libitum fat and protein intake, low-carbohydrate diets are typically hypocaloric either by design or by spontaneous reduction of total food intake. Furthermore, the type of fat has been shown to be much more important than the total amount of fat in the diet.

Whereas saturated fats have been linked with increased CVD risk, the use of monounsaturated fatty acids and polyunsaturated fatty acids have been inversely associated with CVD risk. Therefore, if carbohydrate restriction is accompanied by an increase in unsaturated fats, there will be improvement in glycemic control, insulin sensitivity and dyslipidemia including reduction in LDL cholesterol.

Again, despite acknowledging that “in persons with type 2 diabetes, on weight maintenance diets, replacing carbohydrate with monounsaturated fat reduces postprandial glycemia and triglyceridemia,” current guidelines fall short of recommending these interventions without providing a valid reason for doing so.

Carbohydrate intake and postprandial hyperglycemia

Postprandial hyperglycemia is a risk factor for CVD, particularly in diabetic patients.

Several studies, including the Nurses Health Study, have suggested a link between dietary carbohydrates and CVD risk. Furthermore, control of postprandial hyperglycemia has been shown to provide cardiovascular benefits and to contribute to the overall decrease of HbA1c, which has been clearly shown to reduce microvascular disease in both type 1 and type 2 diabetes.

Dietary carbohydrates are the major determinants of postprandial glucose levels and low carbohydrate intake has been reported to lower postprandial glucose and plasma insulin levels. Furthermore, control of postprandial hyperglycemia with a-glucosidase inhibitors such as acarbose significantly decrease the risk of diabetes in patients with impaired glucose tolerance.

Despite acknowledging these data, current guidelines continue recommend high-carbohydrate intake.

Carbohydrate intake and dyslipidemia

Accumulating evidence indicates that low-fat/high-carbohydrate diets are associated with elevated triglyceride and low HDL cholesterol levels, and may worsen the dyslipidemia of type 2 diabetes and metabolic syndrome.

Conversely, low carbohydrate diets have been consistently demonstrated to lower triglycerides and increase HDL. Even those studies that failed to show significant differences in weight loss between low-carbohydrate diets and low-fat diets after one year show reductions in triglycerides and an increase in HDL cholesterol, indicating that this benefit of carbohydrate reduction is independent of weight loss.

Carbohydrate intake & insulin resistance

Low-carbohydrate diets have been reported to have beneficial effects on the hyperinsulinemia seen in type 2 diabetes and insulin resistant states.

The data are, however, limited by few studies with small number of diabetic subjects and differences in method of measuring insulin sensitivity in various studies. One study demonstrated significant improvement in insulin sensitivity, up to 75%, with a low-carbohydrate diet as measured by euglycemic hyperinsulinemic clamp.

Another study showed that carbohydrate restriction was associated with a significant increase in insulin sensitivity at six months (measured only in nondiabetic subjects) although the difference between the low-fat and low-carbohydrate groups was not statistically significant at one year.

Carbohydrates restriction and reduction in antidiabetic medication

Perhaps the most impressive result indicating the need for reevaluation of dietary recommendations is the demonstration in two small studies that very low-carbohydrate diets can eliminate or reduce the use of antidiabetic medications.

In one study, two patients reduced or eliminated the need for insulin. One patient was able to discontinue sulfonylurea, one patient discontinued metformin and glipizide, and one discontinued metformin and rosiglitazone.

If carbohydrate restriction is accompanied by an increase in unsaturated fats, there will be improvement in glycemic control, insulin sensitivity and dyslipidemia.


In another study, reductions in medications also included insulin, metformin, thiazolidinedione and sulfonylurea.

This dramatic effect should be a wake-up call for diabetologists, although because it is so dramatic, very low-carbohydrate regimens in patients on insulin or oral hypoglycemic agents should be done with close clinical supervision and we are reluctant to recommend them.

Because of the somewhat contentious atmosphere surrounding this subject, I feel obligated to point out that I am not supported or affiliated in any way with any individual or entity that promotes a particular diet.

This editorial is intended to stimulate a scientific and scholarly debate that will lead to more effective dietary recommendations that take account of the current evidence for carbohydrate restriction. This will thereby provide more options to our patients and our society at large in the current struggle with the epidemic of obesity and diabetes, which is claiming thousands of lives daily and leaving many people disabled.

I do not recommend the extreme reduction of carbohydrate, and I believe that the need of the hour is to accept the benefits of carbohydrate restriction with care.

It is also important to establish guidelines for carbohydrate restriction, especially emphasizing the use of mono- and polyunsaturated fats as a way to achieve caloric balance, since these have been inversely linked with CVD risk.

I also believe that clinical trials need to be conducted using graded levels of carbohydrate restriction and fat intake, with special emphasis on unsaturated fats, to examine their effects on weight loss, glycemic control, insulin resistance and CVD.

An open-minded analysis of such experiments is needed to resolve the present controversy about optimal dietary recommendations for patients with diabetes.

For more information:
  • Samy I. McFarlane, MD, MPH, FACP, is an Associate Professor of Medicine and Interim Chief of Division of Endocrinology, Diabetes and Metabolism at SUNY Downstate Medical Center and Associate Medical Editor of Endocrine Today.
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