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The Effects Of Dietary Carbohydrate Restriction On Glucose-Lowering Effect In T2DM

Recent meta-analysis conducted to address ideal amount of dietary carbohydrates in the management of T2DM.

Nutrition management is important in patients with type 2 diabetes. Current recommendations suggest a low caloric diet for overweight patients to achieve weight loss and improve glycemic control, and carbohydrates with a low glycemic index to improve postprandial glucose control, but the ideal amount of dietary carbohydrate in the management of type 2 diabetes is unclear.

An intake of high carbohydrate diet (45–60%) has been previously recommended in patients with T2DM, but a restricted carbohydrate diet has been suggested by some experts in recent years. This suggestion is not supported by the evidence from high-quality randomized controlled trials and the amount and types of carbohydrate, fat, and protein in the low and high carbohydrate diets compared were unclear in these published studies. Conclusions on the efficacy of low carbohydrate diet compared with high carbohydrate diet from recent reviews are thus conflicting with regard to glycemic control and weight loss.

A recent meta-analysis of a high-quality randomized clinical trial aimed to examine the effects of low to moderate amounts of carbohydrate (energy percentage below 45%) in comparison to diets containing high amounts of carbohydrate in patients with type 2 diabetes. Researchers performed systematic literature searches of Cochrane library databases, EMBASE, and MEDLINE in the period 2004–2014 for guidelines, meta-analyses, and randomized trials that assessed the outcomes HbA1c, BMI, weight, LDL cholesterol, quality of life (QoL), and dropout rates.

Researchers have identified 10 randomized trials comprising a total of 1,376 participants with T2DM who were included in this analysis. Forty-nine percent were male and the average age was 58 years. The majority of study subjects had obesity with a mean body mass index range from 26 kg/m2 in an Asian population to 37 kg/m2 in an American population. All trials were conducted in outpatient settings using parallel RCT designs. Study subjects were randomized to the low carbohydrate or high carbohydrate groups to receive comparable nutrition therapy by trained dietitians, with about the same number and frequency of follow-up sessions. The duration of intervention was different between study trials – five randomized trials with intervention duration was 12 months; in two trials, the duration was 3 months; in one trials, it was 6 months, and in two trials, the intervention duration was 24 months.

The study results found that the low to moderate carbohydrate diet group had lower HbA1c compared to the high carbohydrate diet group in the first year of the intervention (3 or 6 months). The great magnitude of the glucose-lowering effect of low to moderate carbohydrate diets in the first year of intervention due to the carbohydrates intake measured as energy percentage. The greater the carbohydrate restriction, the greater the effect of glucose-lowering (R= -0.85, p <0.01). At 1 year or later, HbA1c was similar in both groups. There were no difference in the effects of both diets between groups on LDL cholesterol, adverse effects, BMI/body weight, cardiovascular events, or mortality.

A major strength of this meta-analysis is that researchers used the GRADE approach to a systematic review of high-quality randomized trials; however, limitations are inevitable. Changes in 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 are probably the main factors modifying the effect of low carbohydrate on glycemic control in type 2 diabetes. Also, lack of blinding of subjects and personnel could potentially cause performance bias in the included studies.

Practice Pearls:

  • Low to moderate carbohydrate diets have greater glucose-lowering effect compared to high carbohydrate diets in the first year of intervention.
  • The greater the carbohydrate restriction, the greater glucose lowering.
  • Apart from lowering of HbA1c over the short term, there is no superiority of low carbohydrate diets in terms of glycemic control, weight, or LDL cholesterol.

Reference:

Ole Snorgaard, Grith M Poulsen, Henning K Andersen, Arne Astrup. Systematic review and meta-analysis of dietary carbohydrate restriction in patients with type 2 diabetes. BMJ Open Diabetes Research and Care. 2017 Feb 23

 

Kay Lynn Tran, Doctor of Pharmacy Candidate: Class of 2018; LECOM College of Pharmacy