“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 Xiaowen Wang, a postdoctoral research fellow in the Department of Nutrition at the Harvard T.H. Chan School of Public Health.
Wang will present the findings at NUTRITION 2026, the American Society for Nutrition’s annual meeting, held July 25 to 28 in National Harbor, Maryland. The work pulls apart two things that usually travel together: how good a diet is, and how heavily processed its foods are.
Over 200,000 adults, followed for decades
Researchers drew on three studies that together followed more than 200,000 U.S. adults from the 1980s through the 2020s. They used a framework called the plant-based diet index to score how much each person leaned on plant foods rather than animal products, how healthy the diet was overall, and how processed the plant foods were. The Nova classification system sorted foods by processing level. The people studied were not limited to vegans or vegetarians, though the analysis looked at the plant-derived parts of their diets.
Participants were grouped into four categories:
Healthy and ultra-processed, such as whole grain breakfast cereal with fortified plant-based milk, plant-based yogurt, whole-grain bread and canned fruit. Healthy and minimally processed, such as oatmeal with fresh fruit and nuts, a quinoa and vegetable salad with olive oil, or homemade lentil soup. Unhealthy and ultra-processed, such as fast food, French fries, soda, packaged desserts and refined snacks. And unhealthy and minimally processed, such as white rice, fruit juice, potatoes and homemade desserts made with refined flour and sugar.
What the numbers showed
About half of the participants eventually died or developed heart disease or type 2 diabetes. The risk of those outcomes tracked overall diet quality. Healthy diets were linked to lower risk and unhealthy diets to higher risk. Inside each of those groups, the risks were almost identical whether the foods were ultra-processed or minimally processed.
The researchers say this casts doubt on processing level as a main marker of healthy eating. Nova does not account for nutritional value, so a healthy food can land in the ultra-processed class while a minimally processed one can still be unhealthy.
Many ultra-processed foods are high in added sugars, sodium and refined carbohydrates, which is why heavy consumption often goes with poor diet quality. Others, including fortified breakfast cereals, whole grain products, canned beans and plant-based dairy, can still supply nutrients, fiber and antioxidants. “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,” Wang said.
Her advice: “focus on what you’re eating overall, not just whether it’s processed. 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.”
Wang suggested that dietary guidelines keep promoting established high-quality patterns, such as the Mediterranean diet or healthy plant-based diets, rather than concentrating on processing level. She added that pushing food manufacturers to improve the nutritional content of packaged foods could make healthy plant-based eating more convenient and accessible.
