A new study (in pre-print), conducted by researchers with Aarhus University in Denmark, demonstrated how public health and regulatory initiatives targeting “ultra-processed foods” (UPFs) may have unintended consequences if definitions for the category and mechanistic understandings of processing are not refined.

The term UPFs is typically associated with the four-category NOVA food classification system, which defines Category 4 UPFs as “industrially manufactured food products made up of several ingredients (formulations) including sugar, oils, fats, and salt and food substances of no or rare culinary use.”

For their review, the researchers first analyzed six cohort studies involving more than 635,000 participants and found that associations between UPF consumption and type 2 diabetes risk vary significantly by subtype. While ready-to-eat dishes, meat-based products, and sugar-sweetened beverages were linked to higher diabetes risk, dairy products and sweets showed inverse associations. Other categories, such as breads and cereals, exhibited no clear relationship.

The study also included a post-hoc analysis of the Danish Diet, Cancer, and Health cohort, including more than 57,000 individuals. The researchers investigated the association between adherence to a diet with higher intake of a fictive group of foods, named the “Terrible Five,” comprising processed meat, sugar sweetened beverages, red meat, refined grains, and vegetables. The “Terrible Five” analysis illustrated how grouping diverse foods into a single category can distort findings; associating processed meats and sugary drinks with vegetables produced misleading results, suggesting harm despite vegetables’ known benefits.

The researchers say these findings highlight violations of the consistency assumption, which requires exposures to be well-defined and free of multiple relevant versions. Broad classifications like UPF violate this principle, making effect estimates difficult to interpret and generalize across populations.

Therefore, the researchers suggest that policies such as taxation, labeling, and dietary guidelines based on the accepted understanding of UPFs risk penalizing nutrient-dense foods. They assert that future research should focus on refining UPF definitions, improving dietary assessment tools, and investigating specific processing mechanisms through controlled trials.

“The point of this paper is not to dismiss the value of UPF research to date; it has undeniably advanced our general understanding and sparked important discussions, but rather to emphasize that, if we want to move beyond associational UPF–disease cohort studies and towards a deeper causal understanding of ultra-processing itself, we must recognize the current limitations of the field, whereby causal inconsistency is one of the more important ones,” the study states. “[A proposed] way forward is to put more time and effort into investigating the specific mechanisms by which different processing techniques (not just “ultra-processing” as a broad category) influence short-term intermediate outcomes in tightly controlled randomized trials. Another approach, preferably combined with mechanistic research, is to refine observational research by improving dietary assessment tools to better capture the degree of food processing. These more targeted dietary assessment tools would then enable the use of methods such as food substitution models, contrasting otherwise similar foods that differ primarily in processing degree.”

Without greater precision and mechanistic insight, sweeping UPF policies could undermine public health goals, potentially discouraging consumption of beneficial foods while failing to address the true drivers of disease risk, the researchers conclude.

How a Definition for UPFs Could Shape U.S. Nutrition Policy

In the U.S., efforts at the federal and state levels to define UPFs and regulate the category are underway.

In October, California passed a first-of-its-kind law that establishes the first-ever statutory definition of UPFs and directs California’s Department of Public Health, in cooperation with leading experts from the University of California, to identify and phase out UPFs of concern from schools by 2035. Specifically, the legislation defines UPFs as those “high in” saturated fat, added sugar (or contains a non-sugar sweetener), or sodium, and contains one or more of certain additives, including artificial dyes, flavors, sweeteners, emulsifiers, and thickening agents. Raw agricultural products, minimally processed foods, and pasteurized milk are exempt from the definition of UPFs.

At the federal level, the U.S. Food and Drug Administration (FDA) and the U.S. Department of Agriculture (USDA) are considering public input on the definition of a uniform, recognized definition for UPFs. A joint request for information (RFI) closed in October, which received comments from diverse stakeholders with equally diverse opinions on how—or if—UPFs should be defined, and how the category should be regulated.