The early impact of carbohydrate restriction was clinically significant but not sustained, according to authors of a new meta-analysis.
A diet of low to moderate carbohydrates has a greater effect on glycemic control in type 2 diabetes mellitus (T2DM) compared with high-carbohydrate diets in the first year of intervention. These study results, published in May 2017 in BMJ Open Diabetes Research & Care, show the greater the carbohydrate restriction, the greater the glucose lowering, according to a systematic review.
Tradition: Low-cal, high-carb
Most T2DM patients receive advice to eat a low-calorie diet with the aim of losing weight and improving glycemic control, and to consume carbohydrates with a low glycemic index to improve postprandial glucose control. Traditionally, an intake of 45% to 60% carbohydrate (high-carbohydrate diet) has been recommended, but it’s unclear what is the ideal energy percentage of carbohydrate in the diet, state researchers led by Dr Ole Snorgaard of Department of Endocrinology, Copenhagen University Hospital, Hvidovre, Denmark.
“In recent years … low-carbohydrate diets, have been suggested by some experts and are preferred by some patients,” the authors stated, adding that these diets are believed to lead to improved glycemic control, a quicker and more pronounced weight loss in obese people without diabetes, and a more beneficial effect on lipids.
However, results are conflicting about the efficacy of low-carbohydrate versus high-carbohydrate diets with regard to glycemic control and weight loss.
Low carbs, lower A1c to start
Snorgaard and colleagues conducted a systematic review and meta-analysis and identified 10 randomized trials comprising 1376 participants. In the first year of intervention, a low-carbohydrate diet was followed by a 0.34% lower hemoglobin A1c (A1c) compared with a high-carbohydrate diet.
At 1 year or later, however, A1c was similar in the 2 diet groups. This may be due to patients failing to adhere to the low-carbohydrate diet, or to adaptive mechanisms, they hypothesized.
The effect of the 2 types of diet on body mass index/body weight, LDL-cholesterol, quality of life, and attrition rate was similar throughout the interventions.
The improvement in glycemic control was clinically significant. “It was present after 3 or 6â months of intervention, but not after 1 year or later. The excess reduction in A1c was correlated with the degree of carbohydrate restriction, a finding not reported earlier,” they stated.
The results suggest that a low-carbohydrate diet may be superior to a high-carbohydrate diet with respect to glucose level and postprandial excursions as long the patient adheres to the diet. However, the effect on glycemic control is limited, they noted.
Also, the importance of glucose in the pathogenesis of cardiovascular complications in diabetes is still under debate.
There were limitations to the systematic review. Glucose-lowering medication, the nutrition therapy, the amount of carbohydrate in the diet, glycemic index, fat and protein intake, baseline HbA1c, and adherence to the prescribed diets could all have affected the outcomes, they stated.
The researchers concluded that carbohydrate restriction below 45% has a greater effect on glycemic control in type 2 diabetes than a high-carbohydrate diet in the short term.