Updated 13/09/2026
🟢 Strong Evidence
The quality of plant-based diets matters more than their processing level when it comes to preventing chronic diseases and premature death, according to a major prospective study published in The Lancet Regional Health. The research, which followed 126,842 participants for up to 28 years, challenges conventional wisdom about ultra-processed foods by showing that healthful plant-based diets confer protective benefits regardless of processing status.
Key takeaways
- Healthful plant-based diets reduced mortality risk by 13% in the highest adherence group compared to lowest
- Ultra-processed food content did not diminish the protective effects of quality plant-based eating patterns
- Unhealthful plant-based diets high in refined grains and sugary drinks increased health risks even when minimally processed
Study at a Glance
| Source | The Lancet Regional Health |
| Study type | Prospective cohort study |
| Sample size | N = 126,842 |
| Population | Health professionals aged 24-75 years |
| Country | United States |
Mortality Risk Reduction by Diet Quality
Hazard ratios comparing highest vs lowest adherence groups, 1988-2016
Source: Tong et al., The Lancet Regional Health, 2026 | Georgian Medical Journal News
Major Study Challenges Ultra-Processed Food Assumptions
The research team, led by investigators from multiple US institutions, analyzed data from three major cohort studies: the Nurses’ Health Study, Nurses’ Health Study II, and Health Professionals Follow-up Study. Dr. Yanping Li from Harvard T.H. Chan School of Public Health and colleagues tracked participants from 1988 to 2016, documenting 30,948 deaths during the follow-up period.
The study’s most striking finding challenges the current focus on ultra-processed foods in nutritional epidemiology. “Our results suggest that the overall quality of plant-based diets may be more important than their processing level for chronic disease prevention,” the authors reported in The Lancet Regional Health.
Participants were classified into three distinct dietary patterns: healthful plant-based diets (emphasizing whole grains, fruits, vegetables, nuts, and legumes), unhealthful plant-based diets (high in refined grains, fruit juices, and sweets), and overall plant-based diets (any plant foods over animal products). For more research on plant-based nutrition studies, see our latest coverage.
Processing Level Fails to Override Diet Quality Effects
The researchers employed the NOVA classification system to categorize foods by processing level, from unprocessed to ultra-processed. Surprisingly, when they stratified results by ultra-processed food content, the protective effects of healthful plant-based diets persisted across all processing categories.
Among participants with the highest adherence to healthful plant-based diets, mortality risk remained 13% lower (hazard ratio 0.87, 95% CI 0.83-0.91) compared to those with lowest adherence, regardless of ultra-processed food consumption. The World Health Organization has long emphasized diet quality over processing concerns in its dietary guidelines.
Conversely, unhealthful plant-based diets showed increased mortality risk even when composed primarily of minimally processed foods. This finding suggests that the nutritional profile of foods may outweigh their degree of industrial processing in determining health outcomes.
Chronic Disease Patterns Mirror Mortality Findings
The protective effects extended beyond mortality to major chronic diseases. Participants following healthful plant-based diets showed reduced risks of cardiovascular disease, type 2 diabetes, and certain cancers, with benefits persisting across processing levels.
The study documented 13,836 cardiovascular disease cases and 18,092 cancer cases during follow-up. Healthful plant-based diet adherence was associated with 15% lower cardiovascular disease risk and 10% lower cancer risk in fully adjusted models, according to the published analysis.
These findings align with previous research showing that nutrient density and overall dietary patterns drive health outcomes more than individual food characteristics. For comprehensive coverage of clinical nutrition updates, explore our latest research summaries.
Implications for Dietary Guidelines and Public Health
The study’s findings have important implications for current debates about ultra-processed foods in nutrition policy. While many countries are considering restrictions on ultra-processed foods, this research suggests that promoting high-quality plant foods may be more effective regardless of processing level.
The authors noted that their findings “do not negate the potential harms of ultra-processed foods” but rather highlight that “the quality of the overall dietary pattern may be the primary driver of health outcomes.” The CDC’s dietary guidelines emphasize similar principles of overall diet quality.
Adherence to healthful plant-based diets was associated with 13% lower mortality risk and significant reductions in cardiovascular disease and cancer, regardless of ultra-processed food content.
— Dr. Yanping Li, Harvard T.H. Chan School of Public Health (The Lancet Regional Health, 2026)
What this means
Frequently asked questions
Does this mean ultra-processed foods are safe to eat?
No, the study doesn’t declare ultra-processed foods safe. Rather, it shows that the overall quality of your diet – particularly eating nutrient-dense plant foods – may be more important for health than avoiding all processed foods.
What makes a plant-based diet “healthful” versus “unhealthful”?
Healthful plant-based diets emphasize whole foods like vegetables, fruits, whole grains, nuts, and legumes. Unhealthful versions are high in refined grains, sugary drinks, sweets, and processed plant foods with added sugars and sodium.
How long do you need to follow a healthful plant-based diet to see benefits?
While this study tracked participants for up to 28 years, other research suggests cardiovascular benefits can begin within weeks to months of dietary improvements. The key is consistency in choosing nutrient-dense plant foods over time.
This landmark research reinforces that dietary advice should prioritize food quality and overall eating patterns rather than focusing solely on processing levels. As nutrition science evolves, the emphasis on nutrient density and dietary patterns appears to be the most evidence-based approach for chronic disease prevention. Future research will likely continue to refine our understanding of how different aspects of diet quality interact to influence long-term health outcomes.
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