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The validity and utility of Nova and the concept of ultra-processed foods for science and policy

The Nova classification system has transformed the way researchers think about food. Rather than classifying foods solely by their nutrient content, Nova groups foods according to the nature, extent and purpose of industrial processing. One of its four categories—ultra-processed foods (UPFs)—includes products that undergo multiple industrial processing steps and typically contain ingredients and additives not commonly used in home cooking. The classification has become widely used in nutrition research and has informed dietary guidelines and policy discussions around the world.

Building on this growing body of research, a team of researchers from Wageningen University & Research, Utrecht University, Eindhoven University of Technology, University of Pensylvania, and Voedingscentrum has published a new paper in Nature Food examining the validity and usefulness of the Nova classification for science and public policy. The publication is an important scientific outcome of the Ultra-processed dietary patterns and cardiometabolic health Seed Fund project, funded by the EWUU Institute for Preventive Health, demonstrating how interdisciplinary collaboration can lead to internationally recognised research.

To better understand the key messages behind the publication, we asked lead author Neha Khandpur (WUR) to explain why the Nova classification remains such an important concept for nutrition science and public health.

Ultra-processed foods are a very diverse group of products. How can they still be considered one meaningful category?

“Ultra-processed foods are a heterogeneous group of products. They differ in how they are made, which in turn impacts their form and what they contain. The processing techniques involved in their manufacture, together with the ingredients and additives that are added, change their nutritional profile as well as their molecular and physical structure. This heterogeneity is typical of dietary exposures and reflects the complexity of the human diet. Several dietary exposures share this level of heterogeneity. The value of the category of ultra-processed foods lies in its ability to consistently predict health harms at the dietary level and to inform innovative public policies.”

The Nova classification has also attracted criticism. Why do you think it remains controversial?

“Nova has changed how we think about healthy food, allowing researchers to examine if how the food was processed has any implications for health. The processing of food leads to several changes including to its nutritional composition. This is completely different from how nutrition scientists are used to thinking about food. Many of the critiques levelled at the construct of ultra-processed foods and the Nova classification system are misplaced or misguided. Critics point to the diversity of processing techniques, additives, nutrient and ingredient profiles, and the lack of clearly defined biological pathways.

Similar concerns also apply to many other dietary exposures, where the evidence has nonetheless informed policy. However, in the case of ultra-processed foods, these debates have diverted attention from the compelling evidence we already have on the health harms of ultra-processed diets.

This distraction makes scientists and policymakers cautious about using the evidence for policy action, slowing research and policy innovation. Such delays hinder efforts to improve population diets. Instead, they reinforce food systems dominated by ultra-processed foods, reducing the chance of meaningful health improvements.”

The publication addresses four of the most common criticisms of the Nova classification. The table below summarises the main arguments and explains why they believe these critiques should not prevent the use of the existing evidence in science and policy.

CritiqueImplicationCounterargument
1. Nova imprecisely differentiates between processing techniques.    Researchers risk misclassifying products. This could bias diet-disease effect estimates.  Objective additive and ingredient information are used as proxy markers to identify ultra-processed foods, since processing techniques are not disclosed by manufacturers. The approach for identifying Nova groups for research has demonstrated reliablity and validity. Epidemiology frequently relies on such approaches for identifying conceptual food categories, providing valuable insights into the diet-disease relationship.  
2. The criteria for differentiating between UPF and non-UPF are arbitrary.    Nova has limited utility for research and policy as some foods with balanced nutrient profiles are ultra-processed, and vice versa.  The criteria used to distinguish between UPF and non-UPF for research are independent of a product’s nutrient profile. Human physiological responses, health impacts, preferences or behavioural patterns are not explained by nutrient composition alone.  
3. The biological mechanisms underpinning the health impacts are unclear.Researchers cannot definitively say that “ultra-processing”, per se, causes poor health outcomes. Instead it is likely to be the nutrient profile or strucutral changes.Mechanistic uncertainty does not undermine conceptual validity, predictive utility or epidemiologic consistency. How the product was made impacts several dietary components, including nutritional composition, form and structure. The totality of these changes as encapsulated within the construct of ‘ultra-processing’ has been shown to meaningfully predict health outcomes. Some of these dietary components and their biological responses are already known. Others warrant investigation.  
4. Observational studies provide inconclusive evidence of health harms.Researchers cannot make causal determinations about the health harms of an ultra-processed diet.Observational studies are more conducive to identifying health risks of human diets, compared to randomized controlled trials. Trials have provided emerging evidence of the mechanisitic pathways through which these health risks are likely to manifest. Causal determinations are made from triangulating across multiple sources of evidence – both observational and experimental.  

Despite these ongoing debates, what does the evidence tell us today?

“Free-living people consume many combinations of foods over extended periods of time. Individual foods serve as a vector for a multitude of changes that are a result of the processing they have undergone. When evaluated against the same standards as other dietary exposures, the evidence that diets high in ultra-processed foods harm health is consistent with other available evidence. Taken together, the evidence supports considering precautionary guidance and taking regulatory steps to limit exposure to these products.”

If readers remember just one thing from this publication, what should it be?

”Processing impacts food in important ways that we are only beginning to understand. Some processing, like what is captured in ultra-processed foods, has been linked to long-term health harms in humans. We need more support for research on this topic.”

What are the next steps for this research and the EWUU collaboration?

”We will continue to collaborate to uncover the many biological pathways through which ultra-processed foods impact human food-related behavior and health, and work together to help translate that evidence to inform policy.”

Want to know more?

This interview highlights the key messages of the paper. To explore the evidence and the authors’ full arguments, read the Nature Food publication.

This publication is the result of an interdisciplinary collaboration between researchers from Wageningen University & Research, Utrecht University, Eindhoven University of Technology and international partners. The authors are:

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