Evidence Mounts for Plant-Based Diets in Preventing CVD

Yet another study shows a strong link between a plant-based diet and a lower risk of cardiovascular morbidity and mortality, this time in a population of all-comers, a distinction that the researchers say increases its generalizability.

“Our study adds to a growing body of evidence suggesting that plant-based diets are associated with beneficial health outcomes,” senior author Casey M. Rebholz, PhD (Johns Hopkins Bloomberg School of Public Health, Baltimore, MD), told TCTMD. Past studies have primarily focused on select populations like Seventh-day Adventists or monks who eat particular diets, she said, “so we wanted to conduct this analysis in the Atherosclerosis Risk In Community [ARIC] study because it has a broader generalizability [and] a larger representation of adults living in the US.”

After stratifying more than 12,000 patients from the ARIC study into quintiles how much plant- versus animal-based food they consumed, Rebholz, along with Hyunju Kim, PhD (Johns Hopkins Bloomberg School of Public Health), and colleagues found a 16% lower risk of cardiovascular disease, a 31-32% lower risk of cardiovascular mortality, and an 18-25% lower risk of all-cause mortality over a median follow-up of 25 years among those whose diets were the most plant-based.

With the latest findings, on top of all the prior research in this field, at least one expert is advocating for clinicians not only to recommend the elimination of red and processed meat to their patients, but also to embody that lifestyle themselves.

Andrew Freeman, MD (National Jewish Health, Denver, CO), who was not involved in the study, told TCTMD that the evidence is mounting heavily. “With every one of these studies that comes through that shows this great improvement, isn't it time we arm ourselves with the latest and greatest in technology (ie, nutritional understanding and approaches, lifestyle understanding and approaches) in a way that's really effective and gets people to do it?” he asked. “I would say that one of the key things is that starts with us, meaning that we as providers have to model and example what the behaviors should be.”

Lower CV Disease, Mortality

Published online August 7, 2019, in the Journal of the American Heart Association, the study includes 12,168 middle-aged adults from four US communities who were followed between 1987 and 2016. The ARIC study didn’t directly measure whether participants ate a plant-based diet, but the current analysis reviewed food questionnaires to assign scores of four diet indices. The plant-based diet index (PDI) and provegetarian diet index gave higher scores to higher intakes of all or selected plant foods, while the healthy plant-based diet index (hPDI) gave higher scores only to higher intakes of only the healthy plant foods. The less-healthy plant-based diet index (uPDI) gave higher scores to higher intakes of only the less-healthy plant foods. All indexes gave lower scores to higher intakes of animal foods.

Those in the highest quintiles of the PDI, hPDI, and provegetarian diet index consumed a daily average of 4.1-4.8 servings of fruits and vegetables and 0.8-0.9 servings of red and processed meat; they were more likely to be women, white, high school graduates, and physically active. However, participants in the highest quintile of uPDI consumed a daily average of 2.3 servings of fruits and vegetables and 1.2 servings of red and processed meat; they were more often men, younger, current smokers, and high alcohol consumers.

The incidence of cardiovascular disease events, cardiovascular mortality, and all-cause mortality was lower at higher quintiles of PDI, hPDI, and provegetarian diet index scores, but there was no similar pattern observed across quintiles of uPDI. After adjustment for sociodemographic characteristics, dietary factors, and health behaviors, those in the highest versus lowest quintiles of PDI and provegetarian diet index all had lower risks of incident cardiovascular disease, cardiovascular mortality, and all-cause mortality. Those in the highest versus lowest quintiles of hPDI saw lower risks of CV and all-cause mortality but only a trend toward lower risk of incident CV disease, and no significant associations were observed among any outcome between the highest and lowest quintiles of the uPDI.

Highest vs Lowest Quintile of Each Diet Index

Rebholz explained that they likely didn’t see an effect on the incidence of CV disease in the highest quintile of the hPDI because of how the index codes potatoes.

“There's mixed evidence about potatoes and health outcomes in the literature,” she said. “Ultimately, we believe it comes down to how the potato is prepared and consumed, but in this study, we just had information overall about potatoes, so when we looked at the individual food components that are classified as healthy or unhealthy in this index, potatoes came up as being inversely associated with incident cardiovascular disease. . . . The coding of potatoes as a unhealthy food within this population has diluted the overall expected association between the healthy plant-based diet index and outcomes, specifically incident cardiovascular disease.”

It just continues to add to the overall weight of evidence, which every year seems to get stronger, that a predominantly plant-based diet is one that will make a significant difference. Andrew Freeman

This leads to the broader question of needing to understand the quality of all plant-based foods, because not all are equal, according to Rebholz. “There's been a rise in these more processed plant foods, and I think we don't really understand the health outcomes associated with consuming those foods,” she said. “In our study, dietary intake was assessed several decades ago, so our study is not reflective of the current US food supply, so that's a major topic for future research.”

Plant-Based Diets for Everyone?

“As time goes on,” Freeman said, “the overwhelming preponderance of data is suggesting that the folks who adhere to the most plant-based diets have the least amount of heart disease overall. It wouldn't surprise me if that eventually translates into significant boost in longevity, which has also been shown recently in the literature, and also it wouldn't surprise me if there was also significant reductions in overall death from other causes, (ie, cancer).”

He agreed that the nature of the all-comers design of the study adds more generalizability, but noted that there could still be some bias in the fact that those who chose to participate in ARIC may generally be more concerned about their health overall. Regardless, “it just continues to add to the overall weight of evidence, which every year seems to get stronger, that a predominantly plant-based diet is one that will make a significant difference,” Freeman observed. “As we get into an era of significant cost containment, this is obviously really ripe for the hitting.”

“Without a doubt” physicians should now be advocating for a plant-based diet in all patients, especially since plant-based options seem to be proliferating even among fast food chains, he said. “Wouldn't it be amazing if the most effective tool in our arsenal was lifestyle?” Freeman asked. “The sad part . . . is that very, very few of us are trained with any kind of knowledge or understanding in this space.”