Vegetarian Diets Do Not Lower Mortality Risk, New Research Confirms
TL;DR: A peer-reviewed study published November 26, 2023, in the Journal of Health, Population and Nutrition found no statistically significant reduction in all-cause mortality among vegetarians compared to omnivores in a U.S. adult cohort of 117,673 people tracked for an average of 18 years.
Plant-based diets have long been marketed as a path to longer life. But the most comprehensive U.S. cohort study on the topic to date tells a more complicated story. After rigorously adjusting for age, sex, smoking status, alcohol use, body mass index, physical activity, and socioeconomic variables, researchers found that vegetarians — including lacto-ovo vegetarians, pesco-vegetarians, and vegans — did not outlive their omnivorous counterparts to any statistically meaningful degree.
The findings, reported by News-Medical on November 26, 2023, are likely to reshape how dietitians, public health agencies, and consumers interpret the evidence base for plant-based eating.
The Study: Design, Scale, and Scope
Researchers drew participants from the Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial, one of the largest cancer-screening cohorts ever assembled in the United States. The final analytic sample included 117,673 adults, making it substantially larger than most prior vegetarian-diet studies, which often relied on self-selected, health-conscious communities such as Seventh-day Adventists.
Participants completed detailed dietary questionnaires and were then classified into four mutually exclusive diet groups:
- Omnivores — ate meat, poultry, and/or seafood regularly
- Lacto-ovo vegetarians — excluded meat and fish but consumed dairy and eggs
- Pesco-vegetarians — excluded meat and poultry but ate seafood
- Vegans — excluded all animal products
The cohort was followed for an average of 18 years. Over that period, 39,763 deaths were recorded — a large enough event count to give the analysis substantial statistical power.
Critically, only about 0.7% of participants identified as vegetarians of any type. That demographic skew reflects U.S. eating patterns but also means that vegetarian subgroups were markedly smaller than the omnivore reference group, a limitation the authors acknowledged.
Key Findings: What the Numbers Actually Show
In unadjusted models, vegetarians appeared to enjoy modest survival advantages. However, once the research team applied multivariable adjustments for health-related confounders, those advantages disappeared.
According to the study as covered by News-Medical, the adjusted hazard ratios for all-cause mortality were:
- Lacto-ovo vegetarians vs. omnivores: Not significantly different
- Vegans vs. omnivores: Not significantly different
- Pesco-vegetarians vs. omnivores: A slight reduction was observed in some models, but it became statistically non-significant after full covariate adjustment
The lead author, Dr. Sanchari Sinha Dutta, noted that the null result held across multiple sensitivity analyses, including models restricted to never-smokers and models that excluded early deaths to account for reverse causation.
"Our research indicates that vegetarian diets may not confer the expected mortality benefits, especially when adjusted for various lifestyle variables," Dutta stated.
The full peer-reviewed findings were published in the Journal of Health, Population and Nutrition, making the data available for independent review at jhpn.biomedical.com.
Why Previous Studies Showed a Benefit
For decades, studies — particularly those from Adventist Health Study-2 and the EPIC-Oxford cohort — reported that vegetarians had lower rates of ischemic heart disease, type 2 diabetes, and certain cancers. Some reported modest reductions in all-cause mortality.
But those earlier cohorts share a structural weakness: healthy-user bias. People who self-select into vegetarian diets in Western countries tend to be non-smokers, physically active, highly educated, and health-conscious in multiple other domains. When these confounders are not fully controlled, vegetarian diets can appear protective even if the diet itself is not the primary mechanism.
The PLCO cohort allowed researchers to apply a broader and more granular set of covariates than many earlier studies, which may explain why the apparent benefit vanished after adjustment. As the Journal of Health, Population and Nutrition paper notes, prior studies drawing from religious communities introduced selection effects that made dietary patterns difficult to isolate.
What the Study Does — and Does Not — Mean
This research does not suggest that vegetarian diets are harmful. Nor does it imply that dietary composition is irrelevant to longevity. What it argues, more precisely, is that the independent mortality signal attributed to vegetarianism may have been overstated in prior literature.
Several important caveats apply:
Short-term vegetarians vs. lifetime adherents. The study did not stratify participants by how long they had followed their dietary pattern. Decades of vegetarian eating from early adulthood might produce different outcomes than adoption later in life.
Diet quality within categories. A vegan who lives on white rice, chips, and plant-based processed food is grouped with a vegan who eats whole grains, legumes, and abundant vegetables. Diet quality heterogeneity within labels is a known limitation.
Cause-specific mortality. The analysis focused on all-cause mortality. Prior studies have found stronger protective signals for cardiovascular-specific or cancer-specific endpoints; those sub-analyses were beyond the scope of this paper.
Generalizability. The PLCO cohort skews older and includes a high proportion of white adults. Results may differ in younger, more diverse, or non-U.S. populations.
Public Health and Dietary Guideline Implications
U.S. Dietary Guidelines have consistently endorsed a shift toward more plant-based eating patterns, citing evidence linking reduced meat consumption to lower chronic disease risk. The 2020–2025 Dietary Guidelines for Americans include vegetarian and vegan eating patterns as healthy options supported by the evidence.
This new study does not overturn those guidelines wholesale, but it adds a necessary counterweight: diet label alone does not predict longevity. The totality of one's lifestyle — smoking cessation, physical activity, alcohol moderation, sleep, and stress management — likely matters as much or more than whether one eats chicken.
Public health messaging that frames vegetarianism as a near-guaranteed path to longer life may need recalibration. Dietitians and clinicians are better served by emphasizing overall dietary quality, diversity, and nutrient adequacy rather than categorical exclusion of animal products.
What Should Future Research Investigate?
The authors and independent commentators highlighted several research gaps the PLCO findings open up:
- Duration effects: Do people who have been vegetarian for 20+ years show different mortality patterns than recent adopters?
- Biomarker studies: Do vegetarians show favorable intermediate markers — lipids, glucose, inflammation — even if mortality endpoints are neutral?
- Diet-quality scoring: Using validated indices like the Healthy Eating Index or the Alternative Healthy Eating Index within dietary categories could clarify whether how well someone executes a vegetarian diet modifies outcomes.
- Interaction with genetics: Emerging nutrigenomics research suggests that responses to dietary patterns vary significantly by genetic profile.
The Bottom Line
The largest U.S. cohort study to date on vegetarian diets and mortality found no statistically significant survival advantage for vegetarians after controlling for the lifestyle factors that often travel alongside plant-based eating. The findings, published in the Journal of Health, Population and Nutrition on November 26, 2023, and covered by News-Medical, do not condemn plant-based diets — but they do challenge the narrative that eliminating meat is, by itself, a ticket to longevity.
A well-planned vegetarian diet remains a nutritionally sound choice. But the evidence now suggests that the company your diet keeps — your exercise habits, your smoking status, your sleep — may matter just as much as what is on your plate.
