Exposure to processing from ultraprocessed diets and in feeding studies

Food processing is intrinsic to modern food systems, yet its role in dietary exposures and health outcomes remains difficult to interpret because prevailing classifications treat processing as a categorical property rather than a quantifiable dietary exposure. The introduction of a transformation-based framework that distinguishes physical and chemical modification of foods (Food Processing Levels, FPL) was further complemented to derive Processed Food Intake (PFI)-based descriptors and quantify cumulative exposure to processing across meals and diets. Studies commonly cited in support of ultra-processed food hypotheses exhibit substantial heterogeneity within and between 'unprocessed' or 'ultra-processed' diets. Across studies, diets classified as UPF result in a wide variation in cumulative processing exposure, while substantial overlap is observed between UPF and non-UPF diets when processing is expressed quantitatively. Item-weighted, energy-weighted and nutrients-weighted PFI descriptors capture graded differences that are obscured by categorical classifications and enable comparison of diets matched for nutritional quality yet differing in processing history. Treating food processing as a continuous dietary exposure provides a reproducible basis for analyzing intervention designs, interpreting experimental outcomes, and designing studies that explicitly test the nutritional and health relevance of food processing.