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Clinical research

Vegetarian diets on anthropometric, metabolic and blood pressure outcomes in people with overweight and obesity: a systematic review and meta-analysis of randomized controlled trials

International Journal of Obesity volume 47, pages 903–910 (2023)Cite this article

Subjects

Abstract

Background

It is unknown whether vegetarian diets (VDs) may improve outcomes in people with overweight and obesity.

Objective

To systematically assess the effects of VDs vs. omnivore diets on anthropometric, metabolic, and blood pressure outcomes in people with overweight and obesity.

Methods

We searched for randomized controlled trials (RCTs) in EMBASE, PubMed, Web of Science, and Scopus until February 2, 2022. Primary outcomes were anthropometric risk factors (weight, body mass index [BMI], waist circumference [WC], hip circumference [HC], and body fat percentage). Secondary outcomes were metabolic risk factors (fasting serum glucose, HbA1c, insulin levels) and blood pressure (systolic blood pressure [SBP], diastolic blood pressure [DBP]). Random-effects meta-analyses were performed and effects were expressed as mean difference (MD) and their 95% confidence intervals (CI). The quality of evidence was assessed using GRADE methods.

Results

Nine RCTs (n = 1628) were included. VDs decreased weight (MD −3.60 kg, 95%CI −4.75 to −2.46) and glucose (MD −10.64 mg/dL, 95%CI −15.77 to −5.51), but did not decrease WC (MD −3.00 cm, 95%CI −6.20 to 0.20), BMI (MD −0.87 kg/m2, 95%CI −1.80 to 0.06), or HC (MD: −0.86 cm, 95%CI −3.46 to 1.74). VDs did not decrease HbA1c (MD −0.40%, 95%CI −0.89 to 0.10), insulin (MD −3.83 mU/L, 95%CI −8.06 to 0.40), SBP (MD −0.25 mmHg, 95%CI −2.58 to 2.07), or DBP (MD −1.57 mmHg, 95%CI −3.93 to 0.78). Subgroup analyses by type of VD (four RCTs evaluated lacto-ovo-vegetarian diets and five RCTs vegan diets) showed similar results to the main analyses. QoE was very low for most of the outcomes.

Conclusions

In comparison to an omnivorous diet, VDs may reduce weight and glucose, but not blood pressure or other metabolic or anthropometric outcomes. However, the QoE was mostly very low. Larger RCTs are still needed to evaluate the effects of VD on anthropometric, metabolic factors, and blood pressure in people with overweight and obesity.

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Code availability

R code of meta-analyses may be requested to the corresponding author.

Data availability

The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.

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Author information

Authors and Affiliations

  1. Unidad de Revisiones Sistemáticas y Meta-análisis (URSIGET), Vicerrectorado de Investigación, Universidad San Ignacio de Loyola, Lima, Peru

    Beatriz Melgar, Carlos Diaz-Arocutipa, Alejandro Piscoya, Joshuan J. Barboza & Adrian V. Hernandez

  2. Tau Relaped Group, Trujillo, Peru

    Claudia Huerta-Rengifo & Joshuan J. Barboza

  3. Facultad de Medicina, Universidad Privada Antenor Orrego, Trujillo, Peru

    Claudia Huerta-Rengifo

  4. Hospital Guillermo Kaelin de la Fuente, Lima, Peru

    Alejandro Piscoya

  5. Health Outcomes, Policy, and Evidence Synthesis (HOPES) Group, University of Connecticut School of Pharmacy, Storrs, CT, USA

    Adrian V. Hernandez

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Contributions

BM, AP, and AVH: designed research. BM, CD-A, CR-H, and AVH: conducted research. CD-A, AP, and AVH provided essential materials. BM, CD-A, CR-H, and AVH: analyzed data or performed statistical analysis. BM, CD-A, CR-H, AP, JJB, and AVH: wrote paper. AVH had primary responsibility for final content.

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Correspondence to Beatriz Melgar.

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Melgar, B., Diaz-Arocutipa, C., Huerta-Rengifo, C. et al. Vegetarian diets on anthropometric, metabolic and blood pressure outcomes in people with overweight and obesity: a systematic review and meta-analysis of randomized controlled trials. Int J Obes 47, 903–910 (2023). https://doi.org/10.1038/s41366-023-01357-7

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