Dietary Modulation of the Gut Microbiota in Dogs and Cats and Its Role in Disease Management

Food has a massive influence on the gut microbiota and is one of the most useful therapeutic levers in disease. Recent developments have highlighted how macronutrient balance, food format, and functional ingredients can regulate microbial diversity, metabolism, and host physiology in companion animals such as dogs and cats. This narrative review condenses evidence on the bidirectional gut microbiota–diet connection and on nutritional therapy for gastrointestinal, metabolic, renal, hepatic, and immune-mediated disorders. Protein-based diets including high or hydrolyzed protein, omega-3 acids, fermentative fiber, and probiotics can positively affect microbial composition, stimulate short-chain fatty acid synthesis, and enhance intestinal barrier functions. Conversely, excess fats or refined carbohydrates may cause dysbiosis, inflammation, and metabolic imbalances. Numerous studies have shown that therapeutic nutrition—e.g., low-protein renoprotective, hepatoprotective antioxidants, and allergen-elimination diets—holds enormous potential for treatment. In addition, fecal microbiota transplantation (FMT) can be used as an additive therapy for resistant gastrointestinal illnesses. Despite these developments, constraints remain in terms of standardization, study duration, and species-specific data, especially for cats. This review underscores dietary modification as a clinically actionable tool for microbiota-targeted therapy and calls for integrative, multi-omics research to translate microbiome modulation into precision nutrition for companion animals.