Feeding a bowl of dry kibble is like eating a bowl of dry cereal. How would your body feel if the only thing you ever consumed was dry cereal that had a synthetic vitamin/mineral mix added in? While that might be considered a complete diet containing all the vitamins and minerals needed for survival, it most certainly would not result in vibrant health. Yet this is exactly what 95% of the population is feeding their pets.
How many times have you heard you should shop the outside perimeter of the grocery store? That's where they keep all the fresh fruits, meats, and vegetables. All the center aisles contain the processed foods that are less nutritious. Where is dry kibble found in the food store? YES - in the processed food aisles.
Kibble is made by processing food at high heat, usually being cooked four to five times. Poultry meals (turkey meal, chicken meal, etc) are made by grinding the entire bird, including feathers and feces. Sounds gross because it is. Of course, kibble is not supposed to be contaminated with fecal bacteria, so the ground poultry bodies (along with road kill, dead zoo animals, and other unsavory meats) are cooked at high heat to kill bacteria. After cooking to make a pot of disgusting soup, the soup is dehydrated using heat, to make a meal. The meal is shipped to the pet food manufacturer where it will be combined with the cooked grains and other ingredients, then cooked again to make a dough. The dough is cooked under high heat and pushed through an extruder (shaping die) and cut into kibble sized pieces. Then it is dried again to remove enough moisture to give it a stable shelf life.
Shelf life is great, but how much "life" is left in the food? Because the amino acids, essential fatty acids, and vitamins have been destroyed by cooking, the pet food manufacturers will "fortify" the food with an added vitamin/mineral mix. This mix is usually synthetic and is often imported from overseas. Occasionally excesses of vitamins or minerals are added, resulting in product recalls if enough pets are made ill by the product.
Personally, I prefer to feed my pets raw or gently cooked foods with natural vitamins and minerals, not synthetic additives. When home cooking, be sure to balance the diet with enough calcium and trace minerals from a natural source.