Switching dog food brands frequently is generally not recommended for weight management or any other dietary reason. Sudden changes in a dog's diet can cause digestive upset, including diarrhoea and vomiting, and can also disrupt their nutrient balance, making it difficult to maintain a healthy weight. If you do need to make a change, it should be done gradually over a period of 7 to 10 days by slowly increasing the amount of new food and decreasing the amount of old food in your dog's diet. This will give their digestive system time to adjust to the change and minimise any digestive upset.