 It's not just about digestive upset. Everyone knows that if you're switching the feed, you do it gradually over 7 to 10 days. But what they don't realize is that dog's system is kind of like going on one of those no-carb diets for people or whatever. Your system actually changes. And to switch to a higher-carbohydrate diet in the summer and then switch to a higher-fat diet in the winter, truly you're not doing your dog any favors. You're better off just keeping your dog on a higher-protein and fat diet