The peer-reviewed study, published in the Journal of Animal Physiology and Animal Nutrition, compared fresh, kibble, wet and freeze-dried products purchased in 2024, measuring a range of Maillard reaction products (MRPs), including advanced glycation end products (AGEs) and their precursors.
Researchers from Hacettepe University’s Food Quality and Safety (FoQuS) Research Group analysed 41 dog foods: 15 fresh, 13 kibble, 10 wet, two freeze-dried and one cold-pressed product.
Laboratory analysis focused on:
Statistical comparisons excluded freeze-dried and cold-pressed diets due to very small sample sizes.
Clear differences were observed between food formats, particularly in relation to heat exposure during processing.
Wet foods showed the highest levels of AGEs, with mean CML and CEL concentrations of 92 mg/kg and 128 mg/kg dry matter respectively. These products also had the highest levels of α-dicarbonyl compounds, consistent with greater thermal input.
Kibble diets demonstrated higher lysine blockage (4.9% vs 3.2% in fresh diets), indicating a greater proportion of protein-bound lysine unavailable for metabolism.
Fresh diets, in contrast, had higher total lysine content and generally lower levels of advanced glycation products, although early-stage glycation markers were still present.
Acrylamide was detected in only two kibble samples, and no samples contained detectable levels of certain furfurals.
Across all products, there was no correlation between price category and levels of Maillard reaction products.
This was a cross-sectional survey of commercially available diets, meaning causality between diet type and clinical outcomes cannot be established.
Sample sizes were uneven, particularly for freeze-dried and cold-pressed foods, which limits comparisons across all formats. Storage conditions prior to analysis may also have influenced some results, particularly for glycation products that can continue forming over time.
Importantly, the study did not assess clinical outcomes in dogs, and the health effects of dietary AGEs in companion animals remain an area of ongoing debate. The authors note that evidence from both veterinary and human nutrition is still evolving.
Potential conflicts of interest should also be considered. The study was funded by Dogmates Ltd, and one co-author is employed by Butternut Box, a fresh dog food company. While the paper is peer-reviewed and open access, this commercial involvement may be relevant when interpreting findings.
This study adds to a growing body of evidence suggesting that processing methods—not just ingredients—may influence nutritional quality markers in dog food.
However, the clinical significance of these differences is not yet clear. For now, vets and nurses may wish to be aware of processing as one of several factors to consider when discussing nutrition with clients, alongside established considerations such as life stage, health status and overall diet formulation.
Further research linking these laboratory findings to clinical outcomes will be needed before drawing firm conclusions for practice.
Find the full study here: Journal of Animal Physiology and Animal Nutrition, “A Comparative Analysis of Maillard-Derived α-Dicarbonyl Compounds and Advanced Glycation End Products in Fresh, Wet, Kibble, and Freeze-Dried Dog Foods”, 2026.