Harvard study challenges focus on food processing as key measure of healthy eating

A new Harvard-led study suggests that the overall nutritional quality of a person's diet is more important for long-term health than whether foods are classified as ultra-processed or minimally processed.

• Harvard researchers analyzed dietary and health data from more than 200,000 U.S. adults followed from the 1980s through the 2020s.
• Healthy diets were linked with lower risks of heart disease, type 2 diabetes and death regardless of whether foods were ultra-processed or minimally processed.
• The findings were presented at NUTRITION 2026 and have not yet been published in a peer-reviewed journal.

The research, presented at NUTRITION 2026, the annual meeting of the American Society for Nutrition, found that while many ultra-processed foods are nutritionally poor, the degree of processing alone was not a reliable predictor of long-term health outcomes.

Instead, researchers found that diet quality was consistently associated with the risk of developing cardiovascular disease, type 2 diabetes and premature death.

"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," said Xiaowen Wang, PhD, a postdoctoral research fellow in the Department of Nutrition at Harvard T. H. Chan School of Public Health.

"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."

The researchers analyzed data from three long-running U.S. studies involving more than 200,000 adults between the 1980s and the 2020s. Using a plant-based diet index, they assessed the healthfulness of participants' diets and compared this with the level of food processing using the Nova classification system.

To isolate the effects of diet quality from food processing, participants were grouped into four dietary patterns: healthy ultra-processed, healthy minimally processed, unhealthy ultra-processed and unhealthy minimally processed.

Examples of healthy ultra-processed foods included fortified breakfast cereals with plant-based milk, whole-grain bread, plant-based yogurt and canned fruit. Healthy minimally processed diets featured foods such as oatmeal with fresh fruit and nuts, quinoa salads and homemade lentil soup.

The unhealthy ultra-processed category included fast food meals, soda, packaged desserts and refined snacks, while unhealthy minimally processed diets included foods such as white rice, fruit juice, potatoes and homemade desserts made with refined flour and sugar.

Around half of the study participants either developed heart disease or type 2 diabetes, or died during the follow-up period.

Researchers found that participants consuming healthier diets had substantially lower risks of these outcomes than those eating poorer-quality diets. Within both the healthy and unhealthy dietary groups, however, the risks were similar regardless of whether the foods consumed were classified as ultra-processed or minimally processed.

The findings suggest that nutritional quality may be a more meaningful indicator of healthy eating than processing level alone.

"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," Wang said.

"People should prioritize the quality of foods rather than focusing solely on the level of processing. Aim for more nutrient-dense, high-quality foods to help lower your risk of chronic diseases."

The researchers said the findings support existing dietary guidance that emphasizes established healthy eating patterns, such as Mediterranean and plant-based diets, rather than focusing primarily on food processing. They also suggested that improving the nutritional quality of packaged foods could help make healthier diets more accessible and convenient.

The findings were presented as a conference abstract at NUTRITION 2026 and should be considered preliminary until they are published in a peer-reviewed journal.

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