Low-Carb or Low-Fat Diet May Similarly Affect Weight, A1C in Patients With Type 2 Diabetes CME

From Medscape Medical News CME
Laurie Barclay, MD
Désirée Lie, MD, MSEd

July 21, 2009 — A low-carbohydrate diet may have effects similar to those of a low-fat diet on weight and hemoglobin A1C (A1C) levels in patients with type 2 diabetes, but patients following the low-carbohydrate diet have a greater increase in high-density lipoprotein (HDL) cholesterol levels after 1 year, according to the results of a randomized clinical trial reported in the July issue of Diabetes Care.

"Optimal weight loss strategies in patients with type 2 diabetes continue to be debated, and the best dietary strategy to achieve both weight loss and glycemic control in type 2 diabetes is unclear," write Nichola J. Davis, MD, MS, from the Albert Einstein College of Medicine of Yeshiva University, Bronx, New York, and colleagues. "Prior studies, done primarily in patients without diabetes, demonstrated weight loss outcomes with low carbohydrate diets comparable to that with other diets. Based on the effectiveness of low-carbohydrate diets for weight loss, recent guidelines from the American Diabetes Association state that for short-term weight loss either a low carbohydrate or low-fat calorie-restricted diet may be effective."

The goal of this study was to compare the effects during 1 year of a low-carbohydrate diet and a low-fat diet on weight loss and glycemic control in 105 overweight adults with type 2 diabetes. The main endpoints of the study were weight and A1C levels, and secondary endpoints were blood pressure and lipid profile, measured at 3, 6, and 12 months.

Weight loss occurred faster in the low-carbohydrate group vs the low-fat group (P = .005), with the greatest decrease in weight and A1C levels occurring during the first 3 months. However, both dietary groups had a similar 3.4% weight loss at 1 year, and neither group had a significant change in A1C levels at this time point. Blood pressure was unaffected. Compared with the low-fat dietary group, the low-carbohydrate group had a greater increase in HDL cholesterol levels (P = .002).

"The most relevant point is that there were increases in HDL cholesterol with the low carbohydrate diet," Maria-Luz Fernandez, PhD, a professor of nutritional sciences at the University of Connecticut, told Medscape Diabetes & Endocrinology when asked for independent comment. "This is a very consistent finding in low-carb interventions. HDL cholesterol is most of the time very low in diabetic people so this is a very important clinical implication."

Limitations of this study include greater baseline weight in the low-fat group vs the low-carbohydrate group, possible bias caused by use of single-day dietary recall or a single-day food record to evaluate dietary intake, and lack of objective measures of physical activity.

"Among overweight patients with type 2 diabetes, there was no significant difference in the weight or A1C change in participants after a low carbohydrate compared with a low-fat diet for 12 months," the study authors write. "Participants in both arms achieved an average 3.4% weight reduction but did not reduce A1C. Differences in the short-term effects of each diet were not sustained."

When asked about clinical caveats or recommendations regarding low-carbohydrate diets, Dr. Fernandez said: "Low-carb diets are difficult to follow if the carbohydrate is very low, but a 25% carbohydrate diet is not difficult to follow and it can be very useful for diabetic patients."

In additional research, Dr. Fernandez recommends studies to evaluate whether there are sex responses or if the responses vary depending on low HDL cholesterol levels at baseline.

Diabetes Care. 2009;32:1147-1152.