Low Carbohydrate Diets Best For Diabetes

Researchers, reporting in the journal Nutrition & Metabolism in July 2005, concluded that low carbohydrate diets compare more favorably, at least over the short term, to traditional low fat for improving glycemic control, insulin sensitivity and dyslipidemia of diabetes with reduction in triglycerides, increase in HDL cholesterol and modification of LDL to a less atherogenic form (i.e. a form where LDL Cholesterol is less likely to deposit in the arteries).

At the time of writing their review these researchers, Surender Arora and Samy McFarlane, were from the Division of Endocrinology, Diabetes and Hypertension, SUNY Downstate Medical Center, and Kings County Hospital Center, Brooklyn, NY.

The following does not represent their complete work and is in part extracted and in part adapted from their review.

A low fat, high carbohydrate diet in combination with regular exercise is the traditional recommendation for treating diabetes. Compliance with these lifestyle modifications is less than satisfactory, however, and a high carbohydrate diet raises postprandial plasma glucose and insulin secretion, thereby increasing risk of cardiovascular disease, hypertension, dyslipidemia, obesity and diabetes.

Moreover, the current epidemic of diabetes and obesity has been, over the past three decades, accompanied by a significant decrease in fat consumption and an increase in carbohydrate consumption. This apparent failure of the traditional diet, from a public health point of view, indicates that alternative dietary approaches are needed.

Because carbohydrate is the major agent that promotes secretion of insulin, some form of carbohydrate restriction is a prima facie [at first sight] candidate for dietary control of diabetes. Evidence from various randomized controlled trials in recent years has convinced us that such diets are safe and effective, at least in short-term. These data show low carbohydrate diets to be comparable or better than traditional low fat high carbohydrate diets for weight reduction, improvement in the dyslipidemia of diabetes and metabolic syndrome as well as control of blood pressure, postprandial glycemia and insulin secretion.

Furthermore, the ability of low carbohydrate diets to reduce triglycerides and to increase HDL cholesterol is of particular importance. Resistance to such strategies has been due, in part, to equating it with the popular Atkins diet. However, there are many variations and room for individual physician planning.

Some form of low carbohydrate diet, in combination with exercise, is a viable option for patients with diabetes. However, the extreme reduction of carbohydrate of popular diets (less than 30 grams per day) cannot be recommended for a diabetic population at this time without further study. On the other hand, the dire objections continually raised in the literature appear to have very little scientific basis. Whereas it is traditional to say that more work needs to be done, the same is true of the assumed standard low fat diets which have an ambiguous [doubtful or uncertain] record at best.

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

According to the USDA Continuing Survey of Food Intakes by Individuals (CSFII), the absolute amount of fat and saturated fat consumed has decreased during the obesity epidemic although there is a slight increase for women from 1994 to 1995. (J Am Coll Nutr 1999, 18:207-212).

This apparent failure of low fat diets in curbing the obesity pandemic calls into question the effectiveness and long-term usefulness of such dietary recommendation and has led to renewed interest in alternative dietary interventions, notably those recommending reduced carbohydrate intake.

Low fat diets are generally associated with high carbohydrate intake which in turn is associated with several metabolic abnormalities. (Diabetes 1992, 41:1278-1285, Jama 1994, 271:1421-1428). These metabolic abnormalities are more pronounced in the diabetic population, leading to worsening glycemic control, dyslipidemia and increased inflammation to name a few. (Dyslipidemia may be manifested by the total cholesterol, the “bad” LDL cholesterol and the triglyceride concentrations, and a decrease in the “good” HDL cholesterol concentration in the blood).

Traditionally, increased fat intake has been considered as the main cause for excess energy intake and obesity but the trends in food intake during the obesity epidemic do not support this notion. (J Am Coll Nutr 1999, 18:207-212, Jama 1999, 282:1519-1522).

While fat intake has decreased, carbohydrate intake has increased simultaneously. This rise in dietary intake of carbohydrates, and especially highly refined carbohydrate, is a likely culprit in promoting weight gain and obesity. (Nutr Rev 2000, 58:163-169).

In a recent study, significantly greater weight loss was demonstrated with low carbohydrate intervention (less than 10% calories from carbohydrates) despite higher caloric intake (1855 kcal/day) compared to high carbohydrate (60% calories from carbohydrates) with lower caloric intake (1562 kcal/day). (Nutr Metab (Lond) 2004, 1:13).

Two of the low carbohydrate-low fat comparisons were continued for 1 year. (N Engl J Med 2003, 348:2082-2090, 142:403-411, Ann Intern Med 2004, 140:778-785). It is frequently cited that the difference in weight loss between the low carbohydrate diet and low fat diet was not statistically significant after one year but it should be pointed out that in these studies, participants had the freedom to increase the carbohydrate content of the diet over longer duration and it is reasonable to say that as carbohydrate is added back to the diet, its effectiveness wanes.

For example, in the study by Foster and colleagues at the University of Pennsylvania School of Medicine, Philadelphia, the low-carbohydrate diet produced a greater weight loss than did the conventional diet for the first six months, but the differences were not significant at one year. There was no significant difference in the urinary ketone levels between the two study groups after 3 months, suggesting inadequate carbohydrate restriction during the later part of the study which would contribute to the similarity in various parameters between the groups. In addition, the authors of these studies included subjects who had dropped out of the study. This method, justified under the name “intention to treat analysis” obscures the information in the study and has the effect of making the more effective diet look worse. The researchers did concede that adherence was poor and the drop out rate was high in both groups. (N Engl J Med 2003, 348:2082-2090).

In another recent study comparing the effects of four popular diets including a low carbohydrate diet and a low fat diet, there were no significant differences in weight loss in the different groups at the end of 1 year. However, this study also had the shortcomings of the above studies, including small sample size (40 subjects in each group) and poor adherence in all the groups (30-60% dropouts). The low carbohydrate diet group also failed to reach carbohydrate reduction goals of carbohydrate intake of 190 gm/day at 6 months and 12 months as compared to the start of the study of 239 gm/day. Hence, it is not surprising that weight loss was not significantly different in the low carbohydrate diet group. (Jama 2005, 293:43-53).

What is encouraging is that despite such marginal carbohydrate restriction in the low carbohydrate group, this group was able to achieve a modest weight loss that was comparable to the other diet groups, while maintaining a greater improvement in lipid (cholesterol, triglycerides) profile suggesting that even minimal carbohydrate restriction may have beneficial effects in terms of weight loss and might be offered to those at high risk who fail to lose weight with traditional low fat diets.

Diets containing 50-60% calories from carbohydrates have been the standard recommendation for patients with type 2 diabetes and metabolic syndrome. However, evidence from several population groups studies such as the Nurses Health Study and Health Professional Follow-Up Study has linked dietary carbohydrate intake (measured as glycemic load) with risk of type 2 diabetes and cardiovascular disease. (J Nutr Health Aging 2001, 5:132-138, Diabetes Care 2004, 27:538-546).

Compelling evidence from clinical and metabolic studies demonstrate worsening of glycemic control and dyslipidemia in diabetics with high carbohydrate diets whereas low carbohydrate diets may reverse these serious metabolic abnormalities.

Before the discovery of insulin, dietary carbohydrate restriction was the recommended treatment for diabetes management. (J R Soc Health 1997).

To summarize, the effect of a low carbohydrate diet on glycemic control was significantly greater and occurred independent of weight loss in those studies that were able to achieve and maintain adequate carbohydrate restriction. In other studies, the effect on glycemic control was modest and proportional to the weight loss, and at least comparable to that seen with low fat diets.

In conclusion, a low carbohydrate diet is associated with significant improvement in glycemic control and has the potential for reduction in need for exogenous insulin or oral hypoglycemic medications.

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Extracted and adapted from: Arora SK, McFarlane SI. The case for low carbohydrate diets in diabetes management. Nutrition & Metabolism 2005, 2:16 (14 July 2005). © 2005 Arora and McFarlane; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/2.0 which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The electronic version of this article is the complete one and can be found online at: http://www.nutritionandmetabolism.com/content/2/1/16