Effects of low-carbohydrate- compared with low-fat-diet interventions on metabolic control in people with type 2 diabetes: a systematic review including GRADE assessments

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ABSTRACT

Background

It remains uncertain which diet is best for people with type 2 diabetes (T2D).

Objective

We compared the effects of dietary carbohydrate restriction with fat restriction on markers of metabolic syndrome and quality of life in people with T2D.

Design

This systematic review of randomized controlled trials (RCTs) and controlled clinical trials (CCTs) compares the effects of a low-carbohydrate [≤40% of energy (%)] diet with those of a low-fat (≤30%) diet over a period of ≥4 wk in patients with T2D. Two investigators independently selected studies, extracted data, and assessed risk of bias. The GRADE (Grading of Recommendations Assessment, Development, and Evaluation) approach was used to assess the certainty of evidence. Pooled mean differences (MDs) and 95% CIs were calculated with the use of a random-effects model.

Results

Thirty-three RCTs and 3 CCTs (n = 2161) were included. Glycated hemoglobin declined more in people who consumed low-carbohydrate food than in those who consumed low-fat food in the short term (MD: –1.38%; 95% CI: –2.64%, –0.11%; very-low-certainty evidence). At 1 y, the MD was reduced to –0.36% (95% CI: –0.58%, –0.14%; low-certainty evidence); at 2 y, the difference had disappeared. There is low to high (majority moderate) certainty for small improvements of unclear clinical importance in plasma glucose, triglycerides, and HDL concentrations favoring low-carbohydrate food at half of the prespecified time points. There was little to no difference in LDL concentration or any of the secondary outcomes (body weight, waist circumference, blood pressure, quality of life) in response to either of the diets (very-low- to high-certainty evidence).

Conclusions

Currently available data provide low- to moderate-certainty evidence that dietary carbohydrate restriction to a maximum of 40% yields slightly better metabolic control of uncertain clinical importance than reduction in fat to a maximum of 30% in people with T2D. This systematic review is registered at http://www.crd.york.ac.uk/PROSPERO/display_record.php?ID=CRD42017052467 as CRD42017052467.

Key Words

diabetes
low carbohydrate diet
low fat diet
HbA1c
GRADE

Abbreviations used:

CCT
controlled clinical trial
DTSQ
Diabetes Treatment Satisfaction Questionnaire
GRADE
Grading of Recommendations Assessment Development and Evaluation
HbA1c
glycated hemoglobin
MCS
mental component score
MD
mean difference
PAID
Problem Areas in Diabetes
PCS
physical component score
RCT
randomized controlled trial
T2D
type 2 diabetes
%
percentage of energy.

Cited by (0)

Supported by the Dutch Diabetes Foundation (project 2016.17.1880) and an unrestricted grant from Sanofi (project LUMC/RdG/HdG/MI-14643000041663). The funders had no role in the study design, data collection, data analysis, data interpretation, or writing of this article.