Other than that, it is hard to be sure about any nutritional claims. Studying nutrient needs is extremely complex. For every good thing you hear about a food, there are likely to be as many bad things. Making sense of this is very difficult. Some things seem to be clear, though.
Pets do require certain nutrients.
This is an organization which sets standards for pet foods. Most good quality foods will have this statement on their label. It is at least a good start in ensuring that your pet's diet is adequate. Some people are currently advocating diets containing raw meat for pets. Before feeding raw meat, please stop to consider the health warnings for humans concerning raw meat.