ABSTRACT
BACKGROUND: A total of 374 million adults worldwide are living with prediabetes, 70% of whom will develop type 2 diabetes mellitus (T2DM) in their lifetime. Medical nutrition therapy (MNT) provided by a dietitian, such as that found in lifestyle interventions, has the potential to improve glycemic control and prevent progression to T2DM. OBJECTIVES: The objective of this systematic review was to examine the effectiveness of MNT provided by a dietitian, compared with standard care, on glycemic, cardiometabolic, and anthropometric outcomes in adults with prediabetes. METHODS: Searches were conducted for randomized controlled trials (RCTs) published between 1995 and 2022 using electronic databases MEDLINE, CINHAL, and Cochrane Central. The risk of bias was assessed using version 2 of the Cochrane risk-of-bias tool for RCTs. Meta-analyses were conducted using a random-effects model. The certainty of evidence was assessed for each outcome using the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) method, and a summary of findings table was created using the GRADEpro Guideline Development Tool. RESULTS: Thirteen RCTs were included in the analysis, showcasing a variety of MNT interventions delivered by dietitians. Intervention durations ranged from 3 to 24 mo. Compared with standard care, MNT improved hemoglobin A1c (HbA1c) (mean difference [95% confidence interval]: -0.30% [-0.49, -0.12]) and fasting blood glucose (FBG) (-4.97 mg/dL [-6.24, -3.71]). Statistically significant improvements were found in anthropometrics (weight, body mass index, and waist circumference), cholesterol (total, high-, and low-density lipoproteins), and blood pressure (systolic and diastolic). No significant effect was found on T2DM or triglycerides. The certainty of evidence was moderate for FBG and low for HbA1c and incidence of T2DM. CONCLUSIONS: In adults with prediabetes, MNT was effective in improving glycemic outcomes, anthropometrics, blood pressure, and most lipid levels. However, most studies had a risk of bias because of the randomization process or deviations from intended interventions. MNT plays a key role in improving cardiometabolic risk factors in adults with prediabetes. TRIAL REGISTRATION NUMBER: This study was registered with the registration ID #351421, available from https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=351421.