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Why a Low-Carb Diet Should Be the First Approach in Diabetes Treatment

A panel of medical experts, including our own Advisory Board member Dr. Richard K. Bernstein, presents the evidence for low-carbohydrate diets as initial therapy…

Please note: the following summary was excerpted by Jennifer Piggot, LECOM PharmD candidate, from the original article which can be found here. We encourage all interested readers to look over the full article and supporting research.

The current state of diabetes care in the United States health system shows the inability of existing recommendations to control the epidemic of diabetes, the failure of low-fat diets to improve obesity rates, cardiovascular risk or general health, and the continual reports of serious side effects of commonly prescribed diabetic medications. The success of low carbohydrate diets in the treatment of diabetes and metabolic syndrome without significant side effects point to the need for a reappraisal of dietary guidelines. The immediate benefits of carbohydrate restriction in diabetes patients include reduction of high blood glucose, less requirement for weight loss, fewer side effects than medication therapy and the reduction or elimination of medications. This article outlines the current evidence supporting the use of low-carbohydrate diets as the first approach to treating type 2 diabetes, and an effective adjunct to pharmacology in type 1. These results represent the best documented and least controversial studies.

It is known that diabetics are defective in response to carbohydrates, which can lead to hyperglycemia. Hussain et al. compared a very low carbohydrate ketogenic diet (VLCKD) with a low calorie diet over a 24-week period in diabetics and non-diabetics. Blood glucose dropped more dramatically in the VLCKD group than in those given the low-calorie diet. Patients with type 2 diabetes experienced an average blood glucose level approximately 1mM lower than in the low-calorie diet group. More significantly, the VLCKD group approached normal blood sugar levels after 24 weeks, whereas the other arm of the study saw blood glucose remaining elevated. Finally, the patients participating in the VLCKD achieved an average HbA1c of 6.2% compared to an average of >7.5% for the low-calorie diet group.

Data from the National Health and Nutrition Examination Surveys (NHANES) indicate a large increase in carbohydrates as a main contributor to caloric excess in the U.S from 1974-2000. Dietary carbohydrate intake in men rose from 42% to 49% and, in women, it rose from 45% to 52%. There is data to suggest a correlation of increased carbohydrate intake to increased diabetes diagnoses. These epidemiologic measurements are supported by biochemical mechanisms. Specifically, uncontrolled de novo lipogenesis causes hepatic steatosis which is closely associated with the onset of obesity, insulin resistance, and type 2 diabetes.

Improvements in patients with type 2 diabetes can be seen at any level of weight loss. When the American Diabetes Association recommends low carbohydrate diets, it is with the notion that weight loss will serve as the major benefit. However, a series of well-designed experiments have demonstrated improvements in glycemic control and hormonal and lipid parameters under conditions where patients on a low-carbohydrate diet maintained a constant weight. Results from a recent study indicate that improvement in glycemic control with a low-carbohydrate diet is attained irrespective of weight loss — there is no correlation. Given the difficulties that most people have losing weight, this factor alone provides an obvious advantage to low-carbohydrate diets.

The previous point emphasizes that a low-carbohydrate diet provides benefit in the absence of weight loss. When compared to low-fat diets, low carb diets frequently show dramatically better results. One randomized study compared a low-carbohydrate diet to a “healthy-eating” diet for 3 months in diabetics and non-diabetics. The study reported that almost all participants in the low-carbohydrate diet had a successful weight loss of 2kg as an arbitrary cutoff, while the other arm (the “healthy-eating” diet) only had about half reach that mark. When comparing a VLCKD with a low-fat diet, results showed weight loss was better on the VLCKD than the low-fat diet. Low-fat diets have shown poor results in the long term for patients, and this concept was recently highlighted in the Women’s Health Initiative. In the study, women were instructed to follow a low-fat diet, which resulted in a modest weight loss. However, by the end of the intervention, many regained the weight back.

Adherence to a low-carbohydrate diet, as measured in clinical trials, is usually equal to or better than other diets containing the same number of calories and is comparable with that for many pharmacologic interventions. A comparison of the number of completers of carbohydrate-restricted vs. fat-restricted in 19 studies showed similar behaviors for the two regimens. Adherence, which was better on the low-carbohydrate arms, was attributed to the effect of carbohydrate restriction on satiety and appetite suppression due to behavioral effects and hormones.

A large number of randomized controlled trials (RCTs) have compared higher-protein, lower-carbohydrate diets (HPLCDs) with low-fat diets, and a number of systematic reviews and meta-analyses have assessed efficacy and short term safety. They found that HPLCDs have more favorable effects on weight loss, body composition, resting metabolic rate, and cardiovascular risk than fat-reduced diets. Lower carbohydrate diets were associated with significant decreases in body weight, body mass index, triglyceride (TG) levels, and blood pressure, additionally showing improvements in several other metabolic and lipid indicators.

There is a current lack of evidence showing an association between dietary lipids and risk for cardiovascular disease (CVD). Recent meta-analyses have helped to settle the question of a causal link between dietary lipids and CVD. Conclusions from the studies show no effect with replacement of saturated fatty acids with either carbohydrates or polyunsaturated fatty acids. There were various inappropriate statistical analyses throughout the highlighted studies. In the end, none of the 15 studies on replacing saturated fat with carbohydrates showed any effect on coronary deaths. After reviewing the evidence, it is reasonable to conclude that if there is any risk in replacing carbohydrates with saturated fatty acids, it is still conjectural and long term, and should not override the established and immediate benefit of the replacement.

A significant barrier to the implementation of carbohydrate restriction as a therapy in diabetes management is the traditional fear of the effect on blood lipids and, for example, the tendency of dietary saturated fatty acids to raise blood total cholesterol. The rationale for the concern is from the idea that because dietary saturated fatty acids raised cholesterol and plasma cholesterol, it was assumed that it would cause heart disease. The fallacy is that the data were statistical and did not show a direct causal link. Further ambiguity in the literature continues to rise with the extrapolation from rodent data, though outcomes are not seen in humans.

Carbohydrate restriction is the most effective intervention for reducing all the features of metabolic syndrome. Results from a study comparing a low glycemic index (low-GI diet) with a standard high-cereal diet in 201 people with type 2 diabetes showed a 1.7mg/dl increase in HDL levels for the low-GI diet compared to a 0.2mg/dl decrease for the other arm. Another study comparing a low-GI diet with a VLCKD showed striking outcomes between the two groups. The VLCKD diet showed the greatest decrease in TG as well as in weight, HbA1c, and glucose, and a greater increase in HDL. The two most important factors for success with these diets are adherence and encouragement from the health provider.
Dietary carbohydrate restriction has shown to have such an impact that in one study there are reports of patients reducing or even eliminating medication therapy for their diabetes. In a study with 11 participants on a VLCKD compared to moderate carbohydrate diet, 5 patients were able to reduce or discontinue one medication, and 2 patients were able to discontinue all medications. Two additional studies reported similar results, proving that this result is a feature of the carbohydrate restriction in type 2 diabetics.

The time is now for a reappraisal of dietary recommendations in diabetes management. The benefits of carbohydrate restriction are immediate and well documented. Most objections stem from the proposed dangers of total or saturated fat embodied in the so-called diet-heart hypothesis. It is well established that weight loss, by any method, is beneficial to individuals with diabetes.

The advantages to a low-carbohydrate approach have been recognized, and current knowledge dictates that carbohydrate restriction should be a default in the management of type 2 diabetes care and an adjunct in those with type 1 diabetes. Given the superior outcome of carbohydrate-restricted diets, patients should be encouraged to follow this approach.
In conclusion, the authors recommend that government or private health agencies hold open hearings on these issues in which researchers in carbohydrate restriction can make their case heard.

Practice Pearls:

  • Dietary carbohydrate restriction has the greatest effect on decreasing blood glucose levels.
  • During the epidemic of obesity and type 2 diabetes, caloric increases have been due almost entirely to increased carbohydrates.
  • Benefits of dietary carbohydrate restriction do not require weight loss.
  • Studies show that carbohydrate restriction is the best intervention for weight loss.
  • Adherence to a low-carb diet in people with type 2 diabetics is at least as good as adherence to any other dietary interventions and is frequently significantly better.
  • Replacement of carbohydrate with protein is generally beneficial.
  • Dietary total and saturated fat do not correlate with risk of cardiovascular disease.
  • Plasma saturated fatty acids are controlled by dietary carbohydrates more than dietary lipids.
  • The best predictor of microvascular and to a lesser extent, macrovascular complications in patients with type 2 diabetes, is glycemic control (HbA1c).
  • Dietary carbohydrate restriction is the most effective method of reducing serum triglycerides and increasing HDL.
  • Patients with type 2 diabetes on carbohydrate restricted diets reduce and frequently eliminate medication and type 1 diabetics require less insulin.
  • Intensive glucose lowering by dietary carbohydrate restriction has no side effects comparable to the effects of intensive pharmacologic treatment.

Feinman RD, Pogozelski WK, Astrup A, et al. Dietary carbohydrate restriction as the first approach in diabetes management: Critical review and evidence base. Nutrition. 2015;31(1):1-13. Abstract