Both milk and diet drinks are ok. A word of caution though! Having spent the time on TFR you have cleansed your palate of the taste for certain foods and drinks. Diet drinks though low in cals are still feeding your mental desire for sweet stuff. My advice would be to regard diet drinks as treats and stick with water with a slice of lemon as your main thirst quencher. Now you've reached goa,l look to developing a taste for good healthy options to old stodgy staples that added to your waistline. Personally I believe this helps with long term maintenance of your losses.