Consuming a vegetarian diet lowered LDL-C, HbA1C, and body weight when compared to a usual diet, but did not significantly affect systolic blood pressure levels.
Consuming a vegetarian diet was associated with significant reductions in low-density lipoprotein cholesterol (LDL-C), hemoglobin A1C (HbA1c),and body weight in patients with or at high risk of cardiovascular diseases (CVD), according to a systematic review that was published in the Journal of the American Medical Association.
The meta-analysis was conducted through searches in Embase, MEDLINE, CINAHL, and CENTRAL (Cochrane Central Register of Controlled Trials), as well as hand searches to supplement the existing research, according to the investigators.
Primary outcomes of the review were the mean differences between groups in changes—preintervention versus postintervention—in LDL-C, HbA1C, and systolic blood pressure (SBP). Secondary outcomes were changes in body weight and energy intake in the participants, the study authors wrote.
Twenty-nine articles were ultimately included out of 7871 records that were screened. The sample size ranged from 13 to 291 participants, and there was a mean duration of intervention of 25.4 weeks (range, 2 to 24 months).
Nineteen studies (1661 participants; trial duration, 8 weeks to 2 years) were included in the meta-analysis of LDL-C, the study authors wrote. Consuming a vegetarian diet was associated with significantly decreased LDL-C by 6.6 mg/dL (95% CI, -10.1 to -3.1 mg/dL) in a mean of 6 months of intervention, the results showed.
When compared with a usual diet, LDL-C was lowered by 12.9 mg/dL (95% CI, -21.4 to -4.5 mg/dL) with a vegetarian diet, according to the investigators.
For the HbA1C meta-analysis, 10 studies (778 participants; trial duration, 8 weeks to 6 months) were included. Consuming a vegetarian diet was associated with an overall decreased HbA1C by 0.24% (95% CI, -0.40 to -0.07) in a mean 6 months of intervention, the investigators found. Notably, there was a greater effect observed in studies of people with type 2 diabetes (-0.36%; 95% CI, -0.53 to -0.18).
To examine SBP, the meta-analysis included 14 studies (955 participants; trial duration, 8 weeks to 2 years). The researchers discovered that the pooled effect size of vegetarian diets was not statistically significant (-0.1 mm Hg; 95% CI, -2.8 to 2.6 mm Hg).
Continuing to the analysis of body weight, 16 trials (1395 participants; trial duration, 8 weeks to 1 year) were included in the meta-analysis. Overall, body weight decreased by 3.4 kg in a mean 6 months of intervention (95% CI, -4.9 to -2.0 kg) in individuals randomized to vegetarian diets, the results showed.
The greatest reduction in body weight was observed in people at high risk of CVD (-3.6 kg; 95% CI, -5.8 to -1.4 kg), followed by those with type 2 diabetes (-2.8 kg; 95% CI, -4.2 to -1.4 kg), the researchers found.
Lastly, participants that were on energy-unrestricted vegetarian diets significantly reduced energy intake compared with a usual diet (-275.7 kcal; 95% CI, -376.5 to -175.0 kcal). Investigators found a symmetrical funnel plot of energy intake, suggesting a low risk of publication bias.
The study authors noted that previous findings from pharmacological randomized trials of statins, antidiabetic medications, and antihypertensive drugs have shown definitively that lowering cholesterol, glucose, and blood pressure levels has major anti-atherosclerotic effects.
Prior studies had not stratified populations by the different subgroups included in this review, including disease status, type of vegetarian diet, or a comparison diet, the investigators said.
“Well-designed nutrition clinical trials with comprehensive dietary information are warranted to investigate the full effect of high-quality vegetarian diets in combination with optimal pharmacological therapy in people with CVDs,” the study authors concluded.
Wang T, Kroeger CM, Cassidy S, et al. Vegetarian dietary patterns and cardiometabolic risk in people with or at high risk of cardiovascular disease: a systematic review and meta-analysis. JAMA Netw Open. 2023;6(7):e2325658. doi:10.1001/jamanetworkopen.2023.25658