Seriously? I am losing a bunch of weight, and yes sometimes I go order the double burger from my local burger joint with extra cheese and a diet soda. Guess what? I account for those calories, and I will often skip the fries.
Lets check out nutritional information for mcdonalds --- Double Quarter pounder with cheese -- 740 calories Large fries -- 560 calories. For a total of 1300 calories.
Large soda -- 320calories. So yes, getting that diet soda saves me 320 calorie.s
Since I need 2800 calories per day to maintain, that still leaves me with 1500 calories for the rest of the day to lose weight.
Since you are going to be eating lunch anyways you may be eating an extra what 400 calories by going to mcdonalds instead of a home cooked meal? Since I often skip the fries Ill actually be about the same.