Effect of vegetarian diets on CRP: a systematic review and meta-analysis of randomized controlled trials in adults

Growing evidence suggests vegetarian diets offer several advantages over omnivorous ones. Existing research has reported findings on adherence to various types of vegetarian diets and their effects on C-reactive protein (CRP) levels, but the results have been inconsistent. Current systematic review and meta-analysis of Randomized Controlled Trials (RCTs) was conducted to examine whether an association exists between vegetarian diets and C-reactive protein (CRP). Online databases: Scopus, ISI Web of Science, PubMed, and Google Scholar were searched up to December 2022. The trials were reviewed independently by two authors to select ≥ 3 weeks of RCTs that investigated the impacts of a vegetarian diet versus an omnivorous diet in adults. Studies without a control group, sufficient CRP data, non-adult populations, or combined interventions were excluded. Any discrepancy cases were consulted with an independent reviewer. We included ten RCTs that evaluated the effectiveness of various vegetarian diets (lacto, lacto-ovo, and vegan) on CRP. The meta-analysis of 11 eligible studies involving 545 participants, illustrated that vegetarian diets did not significantly change CRP levels in comparison to the control group (Weighted Mean Difference (WMD): -0.04, 95% CI: -0.23, 0.15; p = 0.683). They're existed homogeneity among the trials (Cochran's Q test, I2 = 0.0%, p = 0.610). The subgroup analyses for intervention type, baseline CRP, and trial duration did not show statistically significant effects. Using RoB 2, five of the ten included trials showed some concerns for overall risk of bias, while the remainder were at low risk. The present study did not reveal a significant beneficial effect, regarding following the vegetarian diets on CRP. Some limitations include CRP often reported as a secondary outcome, lack of blinding, sensitivity of results to individual studies, and variability in CRP measurement methods. Carefully structured trials are still needed to endorse the present results. Trial registration PROSPERO registration no. CRD42023397406.