Two reasons! 

  1. A major part of every detox is to ascertain which foods may be causing irritation of your gut/digestive system or causing your weight loss too slow. Only eating 1 vegetable and 1 protein at a time makes it easier to pinpoint which foods are causing these problems. 
  2. Detoxing is also all about reducing the load on your body. By eating a simplified diet, you are reducing the impact on your digestive system, and your body is better able to cleave and break down your food.