I'd be worried about following this type of plan because you aren't getting all of the nutrients your body needs to function every day. One food group isn't going to provide you with the vitamins and nutrients you need to be healthy.
Also, I wouldn't think this would be sustainable as a lifestyle change. I don't think anyone wants to have "milk only" days for the rest of their life!
Maybe you could modify this by trying to eat appropriate amounts from each of the categories every day? Just a suggestion!