Plant-based diets have become popular for their health and environmental benefits. 

However, these benefits may vary based on the quality of the plant foods and other foods that make up the diet. A recent study at VUMC analyzed the association of plant-based diet patterns with mortality in over 77,000 mostly Black and low-income participants in the Southern Community Cohort Study, which started in 2002.  

Dietary intakes were assessed using a validated, 89-item food frequency questionnaire. The investigators generated three measures to assess the association of diet and risk of premature death: an overall plant-based diet index (PDI) that included both healthy plant foods (such as whole grains, fruits and vegetables) and unhealthy plant foods (such as fruit juices, refined grains and potatoes); a healthy plant-based diet index (hPDI); and an unhealthy plant-based diet index (uPDI).  

The study follow-up was through 2022 with a median duration of almost 17 years. The investigators identified over 26,000 deaths during the duration of the study. The highest PDI and hPDI scores were associated with reduced mortality; while the highest uPDI scores were associated with elevated mortality. 

The findings were reported in the The American Journal of Clinical Nutrition, a journal of the American Society for Nutrition. They show a strong association between high quality plant-based diets and reduced mortality rate among low-income populations, suggesting that efforts to promote diets high in healthy plant foods and low in animal foods could improve health outcomes. 

Wei Zheng, MD, PhD, MPH, the Anne Potter Wilson Professor of Medicine and director of the Vanderbilt Epidemiology Center, is the corresponding author of the study. Fangcheng Yuan, a graduate student in the PhD Program in Epidemiology, is the first author. 

This work was supported by the National Cancer Institute, part of the National Institutes of Health (grant U01CA202979).

Guillermo Sanchez, PhD, is a staff scientist in the lab of Nick Zachos, PhD, associate professor of Surgery and Cell and Developmental Biology at Vanderbilt University.

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Walking fast for just 15 minutes per day reduced the risk of death in a large study group of mostly low-income participants. 

The research findings, published July 29 in the American Journal of Preventive Medicine, support promoting brisk walking as a strategy for improving health outcomes in all communities. 

Although the health benefits of walking are widely recognized, there has been limited research on the effect of factors such as walking pace on mortality, particularly in low-income and Black populations, said the study’s senior author, Wei Zheng, MD, PhD, MPH, the Anne Potter Wilson Professor of Medicine and director of the Vanderbilt Epidemiology Center. 

“This is one of the few studies to quantify the effect of daily walking on mortality in a low-income and predominantly Black U.S. population,” said Zheng, who also directs the Division of Epidemiology at Vanderbilt University Medical Center. “By demonstrating the benefits of fast walking — which is a low-cost and largely accessible activity — we provide direct evidence to inform targeted public health interventions and policies to improve health outcomes.” 

The study analyzed data from the Southern Community Cohort Study (SCCS), which enrolled about 85,000 participants ages 40-79 between 2002 and 2009. Most participants (86%) were recruited in collaboration with community health centers serving low-income populations across 12 southeastern states. Participants provided baseline information, including daily walking pace and time, demographic and lifestyle factors, and medical history, using structured questionnaires. 

The current study, led by first author Lili Liu, PhD, MPH, included data from 79,856 of the SCCS participants (racial groups: 66% Black, 30% white, 4% other). In the baseline survey, participants reported the average amount of time per day (in minutes) they typically spend “walking slowly (such as moving around, walking at work, walking the dog or engaging in light exercise)” and “walking fast (such as climbing stairs, brisk walking or exercising).”

The cohort was linked to the National Death Index to obtain vital status and cause of death information through Dec. 31, 2022. Over a median follow-up of 16.7 years, 26,862 deaths occurred. 

The researchers found that fast walking as little as 15 minutes per day was associated with a nearly 20% reduction in total mortality. Slow walking more than three hours per day was associated with a smaller reduction in mortality. The benefit of fast walking remained strong even after accounting for other lifestyle factors, such as leisure-time physical activity levels. 

In addition to reducing premature death from all causes, fast walking reduced death specifically from cardiovascular diseases — the No. 1 cause of death in the United States. The researchers suggested that fast walking might reduce cardiovascular mortality by improving the heart’s efficiency and output, and by reducing the prevalence of obesity and its associated cardiovascular risks such as hypertension and high cholesterol. 

“Brisk walking offers a convenient, accessible and low-impact activity that individuals of all ages and fitness levels can use to improve general health and cardiovascular health specifically,” Zheng said. 

The authors acknowledge that self-reported data on daily walking may have included other types of physical activity, which could introduce misclassification errors. Also, the physical activity data was only collected at baseline, so changes over time could not be considered. The study’s long follow-up and large sample size contribute to “robust and reliable estimates,” they noted. 

Other VUMC co-authors are Guochang Jia, PhD, Martha Shrubsole, PhD, Wanqing Wen, MD, MPH, and Staci Sudenga, PhD. The research was supported in part by the National Institutes of Health (grant U01CA202979).

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A grant from VoLo Foundation will augment federal funding for the Southern Environmental Health Study, an initiative to determine whether environmental exposures are contributing to cancer cases in the region.

The study received its initial funding from the National Cancer Institute and the Vanderbilt-Ingram Cancer Center. A grant from VoLo Foundation — a private nonprofit organization dedicated to accelerating global impact through science-based solutions, education enhancement, and health improvement initiatives — will allow investigators to recruit additional participants and conduct methylation- and proteomics-based biological aging assays to check for biomarkers of early disease risk.

On cancer incidence and mortality maps, some of the highest rates in the country appear in the southern U.S., but whether environmental exposures are a contributing factor has not been scientifically determined. The study is a long-term cohort investigation that will follow participants for at least 10 to 20 years. The participants are between the ages of 40 and 70 and live in Alabama, Arkansas, Delaware, Florida, Georgia, Kentucky, Louisiana, Maryland, Mississippi, Missouri, North Carolina, Oklahoma, South Carolina, Texas, Tennessee, Virginia, West Virginia or the District of Columbia.

“Humans are exposed to large numbers of chemicals and their mixtures with more than 80,000 chemicals having been registered by the Environmental Protection Agency,” said Wei Zheng, MD, PhD, MPH, the Anne Potter Wilson Professor of Medicine and the director of the Vanderbilt Epidemiology Center. “However, very few of them have been adequately investigated in relation to human cancers and other diseases in epidemiologic studies. There are considerable challenges in studying environmental exposures in epidemiologic studies.”

Participants will wear silicone wristbands designed to collect chemicals, which researchers will use to measure exposure to approximately 500 compounds. They will also analyze blood samples to assess the internal exposome using both liquid chromatography and gas chromatography with high-resolution mass spectrometry, allowing them to detect approximately 1,500 confirmed chemicals and endogenous metabolites. To identify potential environmental carcinogens, the researchers will use an innovative exposome-wide association study to link chemical exposures with disease biomarkers, including indicators of biological aging and inflammation.

“Supporting the Southern Environmental Health Study aligns with our mission to advance data-driven solutions that can lead to healthier, more resilient communities. This research has the potential to uncover possible links between environmental exposures and chronic diseases,” said David Vogel, co-founder and chief scientist of VoLo Foundation.

Vogel and his wife, Thais Lopez Vogel, formed the VoLo Foundation in 2014.

“We are very grateful for the support of the VoLo Foundation and believe that this study will generate significant amounts of novel data regarding potential impacts of environmental exposures on human health and pave the way for future studies in this important area,” Zheng said.

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