Health risks of plant-based diets may depend more on meal quality than levels of food processing, according to a study presented at Nutrition 2026.

The study of more than 200,000 people found that the overall quality of a person's diet was associated with their risk of cardiovascular disease (CVD), type 2 diabetes (T2D), and death. However, these associations did not appear to differ much based on food processing levels.

"While many ultra-processed foods tend to be of poor nutritional quality and should generally be limited or avoided, processing itself is not inherently harmful," study presenter Xiaowen Wang, PhD, a postdoctoral research fellow in the Department of Nutrition at Harvard T. H. Chan School of Public Health, said in a press release. 

Individuals should "focus on what you're eating overall, not just whether it's processed," she noted. "A healthy plant-based diet rich in whole grains, fruits, vegetables, nuts, legumes and healthy plant oils is beneficial, even if it includes some processed foods."

Healthy Diets Tied to Lower Risk, Despite Processing

For the study, researchers separated overall diet quality from the level of food processing, using data from three US cohorts that include ed a total of 160,690 women and 42,585 men who were free of cancer, CVD, and T2D at baseline. They used the Plant-based Diet Index to assess the degree to which each participant emphasized plant versus animal food products in their diet; the overall quality or healthfulness of their diet; and their consumption of plant-based foods across various processing levels. 

To enable consistent comparisons, the analysis focused only on the plant-derived components of participants' diets rather than animal-derived foods.

After assessing each participant's overall diet and using the Nova classification system to categorize the processing level of the foods they ate, researchers grouped participants according to their plant-based eating habits: 

• Healthy/ultra-processed (for example, whole-grain breakfast cereal with fortified plant-based milk, plant-based yogurt, whole-grain bread, and canned fruit);
• Healthy/minimally processed (for example, oatmeal with fresh fruit and nuts, quinoa and vegetable salad with olive oil, and homemade lentil soup);
• Unhealthy/ultra-processed (for example, fast-food meals, french fries, soda, packaged desserts, and refined snacks); and
• Unhealthy/minimally processed (for example, white rice, fruit juice, potatoes, and homemade desserts made with refined flour and sugar).

The researchers documented 26,209 cases of CVD; 21,006 cases of T2D; and 55,493 deaths. These outcome risks varied depending on overall diet quality — that is, healthy diets were associated with lower risk, while unhealthy diets were associated with higher risk. 

Within each category, however, the risks were almost identical regardless of whether the diet was ultra-processed or minimally processed. Both healthy ultra-processed and minimally processed diets were significantly associated with a lower risk of CVD (hazard ratio [HR] comparing the highest with the lowest quintiles of scores: 0.86 and 0.82, respectively); T2D (HRs: 0.67 and 0.66); and mortality (HRs: 0.89 and 0.93). 

On the other hand, unhealthy ultra-processed and minimally processed diets were associated with significantly higher risks of CVD (HRs: 1.21 and 1.17) and T2D (HRs: 1.14 and 1.11), while only unhealthy ultra-processed diets were significantly associated with higher mortality (HR 1.07).

The results call into question using processing level as a key indicator of healthy eating, according to the authors. Since the Nova classification doesn't consider the nutritional value of foods, healthy foods can be classified as ultra-processed while minimally processed foods can still be unhealthy. 

"Advising people to universally 'avoid ultra-processed foods' can lead to lower diet quality since healthy ultra-processed foods are beneficial and unhealthy minimally processed foods are detrimental," said Wang. "People should prioritize the quality of foods rather than focusing solely on the level of processing."

'Processed Foods Are Needed'

While expert commentators agreed that food processing alone should not be the main consideration for assessing meal quality, they also pointed to study limitations.

Seamus Higgins, associate professor in Food Process Engineering at the University of Nottingham, UK, commented, "The study suggests that processing alone is not the whole story, but neither does it demonstrate that processing can be disregarded. Food structure, formulation, nutrient quality, the sensory characteristics of food — including taste, texture and aroma — and the biological and psychological drivers of food choice are all closely intertwined, making it difficult to attribute health outcomes to any single characteristic."

"A further limitation," he said, "is that the analysis focused on the plant-derived components of participants' diets rather than the whole diet. As animal-derived foods make a substantial contribution to typical US dietary patterns, caution is needed before generalizing these findings to overall diets."

Alberto Fiore, PhD, professor in Food Chemistry and Technology at Abertay University, Scotland, said the study "confirms directly what has long been suspected: a fortified wholegrain cereal and a can of cola should never have been treated as equivalent health risks simply because both happen to sit in the same [NOVA] processing category, and this study now has the data to demonstrate that error empirically rather than just argue it conceptually."

Another commentator, Aisling Daly, PhD, senior lecturer in Nutrition at Oxford Brookes University, UK, said she would be "interested to know if any comparison with non-plant- based diet indices were conducted, or why not, since this would help add further weight to the discussion around nutrient content or processing levels." 

"Processed foods are needed in the diet, and for many people they are essential for convenience, cost-efficiency, and food preservation reasons," she noted. "The current narrative that 'processed foods are bad' is not accurate and is damaging and worrying for people who need to rely on these foods."

The study was funded by the US National Institutes of Health. Wang, Higgins, Fiore, and Daly declared no conflicts of interest. 

Marilynn Larkin, MA, is an award-winning medical writer and editor based in New York City whose work has appeared in numerous publications, including Medscape Medical News and its sister publication MDedge, The Lancet (where she was a contributing editor), and Reuters Health.