Unfortunately there is no definitive answer to this. Generally we would not suggest consuming any two products that contain the same active ingredients, this is because there is a chance that you may overdo some of the active ingredients. I stand by this, however, some people do choose to combine a diet protein with say, some CLA or l- carnitine for example, this is dependent on the individual and their tolerance of these ingredients. Therefore should you wish to do this we encourage you to do it gradually at first and assess your tolerance.
Generally though, a diet protein such as PhD Nutrition Diet Whey, or Optimum Health Diet Protein contains ample amounts of each ingredient and can help strip off excess layers of body fat very effectively on their own. Another way to go about this is to opt for a low carbohydrate, low sugar and low calorie protein, and combine this with a fat metabolising/ burning supplement.