What should I feed my Shih Tzu to ensure optimal health and longevity? Given the unique dietary requirements of this small yet spirited breed, what specific nutrients are vital in their daily regimen? Should I focus on high-quality commercial dog food or consider home-cooked meals that might offer a more tailored nutritional profile? Moreover, how do I determine the perfect balance of proteins, fats, and carbohydrates to cater to their distinct energy levels and metabolism? Are there particular ingredients that should be strictly avoided, such as those that may trigger allergies or digestive issues in Shih Tzus? As they can be prone to certain health concerns, how do I integrate specialized diets that support their overall well-being? Additionally, how often should I feed them throughout the day to maintain a stable energy level without risking obesity? What portion sizes align best with their age, weight, and level of activity?