Metabolic profiles show few differences in serum amino acid, one-carbon, and fatty acid compounds in dogs fed a plant-based (“vegan”) or meat-based diet

Introduction Dogs are omnivores, not herbivores, and yet entirely plant-based diets are formulated to meet their current known nutrient recommendations. However, little is known about the metabolic effects of feeding diets containing no animal-derived nutrients. Metabolomics allows for the investigation of dietary influences on animal metabolism and physiology beyond what may be revealed by routine healthcare assessments. Methods This study compared serum metabolomics in a longitudinal trial involving 61 healthy adult dogs fed an experimental extruded plant-based (“vegan”) diet (PLANT, n = 31) or a commercial extruded meat-based diet (MEAT, n = 30) for 3 months. Both diets met industry nutrient recommendations for maintenance of adult dogs and had similar levels of total protein and fat, though amino acid and fatty acid profiles differed. Free amino acid and protein, one-carbon, carbohydrate, fatty acids, and lipid metabolites were analyzed at the start and end of the trial. Organic acids and lipid metabolites were measured using direct injection liquid chromatography tandem mass spectrometry, one-carbon, and folate pathway metabolites by liquid chromatography-multiple reaction monitoring mass spectrometry, and fatty acids by gas chromatography. Repeated measures mixed modeling assessed metabolite differences between diet groups over time. Results In total, 11 of 47 amino acid and protein metabolites, 0 of 16 carbohydrate metabolites, 3 of 29 one-carbon/folate pathway metabolites, 21 of 61 fatty acids, and 27 of 78 lipid metabolites differed between diets. Dogs maintained on PLANT demonstrated few changes associated with sulfur amino acid metabolism, but unexpectedly showed a reduction in the serum branched-chain amino acids (BCAA) isoleucine and valine despite higher dietary provision, though no differences in BCAA ketoacids were found. A reduction in serum creatinine without corresponding changes in creatine was also observed in the PLANT group, along with a lower total serum FA and omega-6 to omega-3 FA ratio, despite higher fat content in PLANT. In summary, dogs fed PLANT for 3 months showed few metabolic alterations compared with dogs fed MEAT; those detected were mostly attributable to differences in dietary composition. Discussion This study demonstrated a few differences in nutrient metabolism attributable to the presence or absence of animal products in the diet over 3 months in adult dogs. Based on these findings, further research is warranted using plant-based diets of varying nutritional composition to determine longer-term physiological impacts and how these may affect and be affected by different life stages and health outcomes.