Decreases in medication dose with vegetarian diet
Although most patients were taking medications to manage hypertension, hyperglycemia, and/or dyslipidemia at trial enrollment in as many as eight of the studies, the vegetarian diet intervention resulted in a decrease in medication dose.
In fact, medication use could obscure the favorable effects of vegetarian diets, which could have a larger effect size, the authors speculate.
“This hypothesis is supported by two randomized controlled trials in our meta-analysis that required patients not to take medication that could influence cardiometabolic outcomes, [and] these studies significantly improved systolic blood pressure and LDL-C,” they write.
Not all vegetarian diets are healthy
Although there are numerous variations in vegetarian diets, ranging from vegan diets that eliminate all animal food to pesco-vegetarian diets that allow fish or seafood, most that are well-balanced can provide health benefits including lower saturated fat, L-carnitine, and choline (precursors of the atherogenic TMAO), and other benefits that might explain the improvements seen in the meta-analysis.
The diets may also be high in dietary fiber, mono- and polyunsaturated fatty acids, potassium, magnesium, and phytochemical, and have lower glycemic index scores.
Of note, 12 studies in the meta-analysis emphasized low-fat content, which the authors speculate may have contributed to the improvements observed in LDC-C.
Specifically, lacto-ovo vegetarian diets were associated with the greatest reduction in LDL-C (–14.1 mg/dL); however, four out of five of the trials restricted energy intake, which could have also played a role in improvements.
Importantly, not all vegetarian diets are healthy, and the authors caution about some that allow, for instance, deep-fried foods rich in trans-fatty acids and salt, such as tempura vegetables, potentially increasing the risk of type 2 diabetes and coronary heart disease.
They note that “more than one-third of the studies included in our meta-analysis did not emphasize the importance of consuming minimally processed plant-based whole foods.”
Overall, however, the fact that the greatest improvements in A1c and LDL-C were seen in patients with type 2 diabetes and those at high risk of CVD “highlight[s] the potential protective and synergistic effects of vegetarian diets for the primary prevention of CVD.”
A version of this article first appeared on Medscape.com.