Vegetarian Diets Decrease Cardiometabolic Risk in Patients With High Risk for CVD

Significant improvements in low-density lipoprotein cholesterol (LDL-C), hemoglobin A_1c (HbA_1c), and body weight beyond standard therapy are associated with consuming a vegetarian diet in individuals at high risk for cardiovascular diseases (CVDs), according to findings published in the Journal of the American Medical Association Network Open.

Investigators sought to examine the effect of vegetarian diets on outcomes among people at high risk for CVDs.

They conducted a systematic review and meta-analysis searching MEDLINE, CINAHL, Embase, and CENTRAL databases from inception through July 2021. They included randomized clinical trials (RCTs) investigating vegetarian diets in adults with high risk for CVDs and measuring LDL-C, HbA_1c, or systolic blood pressure (SBP).

The investigators included 20 RCTs (N=1878; range of mean ages, 28-64 years) with a mean intervention duration of 25.4 weeks (range, 2-24 months). Studies were conducted primarily in the US, plus 3 in Asia, 2 in Europe, and 1 in New Zealand. Sample sizes ranged from 13 to 291 participants. Different vegetarian diets were applied across studies, some excluding all animal proteins (except non-fat dairy and egg whites), vegan diets (excluding all animal products and some studies adding vitamin B12), lacto-ovo-vegetarian diets, and lacto-vegetarian diets.

Overall, consuming a vegetarian diet for an average of 6 months was associated with decreased LDL-C (-6.6 mg/dL; 95% CI, -10.1 to -3.1), HbA_1c (-0.24%; 95% CI, -0.40 to

-0.07), and body weight (-3.4 kg; 95% CI, -4.9 to -2.0), in meta-analyses, relative to all comparison diets. The association between a vegetarian diet and SBP was not significant (-0.1 mm Hg; 95% CI, -2.8 to 2.6). The investigators noted a statistically significant among-study heterogeneity in the 19 studies included in the changes in LDL-C meta-analysis. In the 10 studies included in the changes in HbA_1c meta-analysis, heterogeneity was not statistically significant.

Among the various vegetarian diets, the greatest reduction in LDL-C was found in lacto-ovo-vegetarian diets (-14.1 mg/dL) though 80% of these RCTs restricted energy intake. Participants at high risk for CVDs had the most consistent reduction. Compared with usual diet, vegetarian diets significantly lowered LDL-C by 12.9 mg/dL. Compared with active controls, the association of vegetarian diets with LDL-C is not significant.

Participants following a vegan diet had a reduction in HbA_1c compared with the usual and the conventional energy-restricted diabetic diet. Vegetarian diets were associated with improved HbA_1c even in studies with no physical activity prescription.

The investigators noted significant very high among-study heterogeneity in the 16 studies included in changes in body-weight meta-analysis. Greatest weight reduction was noted in participants at high risk for CVD. Diets without energy restriction had greater weight reduction than diets with energy restriction (-4.7 kg vs -1.8 kg).

A moderate level of evidence for LDL-C and HbA_1c reduction was noted with the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) tool.

Limitations of the study include using limited trials with limited participants investigating vegetarian diets in patients with CVDs, and many of the subgroup analyses were conducted with underpowered sample sizes.

“…consuming a vegetarian diet was associated with significant improvements in LDL-C, HbA_1c, and body weight beyond standard therapy in individuals at high risk of CVDs,” the investigators wrote. “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.”