There’s no rock-hard evidence to support that pets are healthier when they eat a variety of foods. However, variety can have some advantages, It can help keep your pet from getting locked into one type of food and can help make it easier to make changes to his diet if necessary. Just be careful to switch diets slowly, taking several days to gradually introduce a new one. And also watch carefully for vomiting, diarrhea or other signs of gastrointestinal upset.