Veterinarians are taught several aspects of nutrition in veterinary school. They are taught how to evaluate claims made by foods, and how to explore if a food is at least halfway decent. They are taught the basic nutritional needs of different species. They are taught that the animals’ best interest is the overriding concern with any recommendation.
There is a lot of misleading and wrong information on the internet. Much of it appears legitimate if you don’t know better. There is also a lot of good information, some of which is poorly presented and may look wrong.
When looking at pet nutrition, it really is the big 3 companies who have the knowledge: Hills, Royal Canin, and Purina. These companies are big enough to:
- Employ veterinary nutritionists (veterinarians with additional training in nutrition)
- Operate feeding centers, actually feeding animals new formulas for months, with frequent examinations and blood tests to see the effect of the formula on the animals
- Manufacture their own foods, which means having control over each and every batch - what goes into the batch, and how it is processed
- Maintain fixed formulas, so every batch is the same
The rest of the companies often are marketing-driven, not nutrition-driven. They design formulas that have a great-sounding ingredient list… but US regulations allow them to vary from that ingredient list for short periods without changing the label. This means your “all-beef” diet can be all, and the “grain-free” diet can contain wheat, rice, etc for weeks. They also use contract manufacturers, so they give up a lot of control over the quality of the ingredients going into each batch, and of the final product.
The reason most veterinarians recommend diets from Royal Canin, Purina, and Hills is because these doctors know the value of proper nutrition, and see it in practice with their patients.