First of all its important to understand what is diet. Diet is not eating boiled food, less food or not eating any food. Whatever you eat on regular basis is your diet. So when you say you are on diet does not actually mean that you are eating healthy or as per your body's requirement. The right thing would be to say " I am eating right and healthy". When you try to be on any specific diet restriction, you have to make sure that if that restrictions can be followed for life long then that is the right way to eat. If you feel it can just be a temporary change then it will not give you sustainable results.