You could not rely on McDonald's for all your meals without surgery.  You certainly can if you pay attention to the nutrition sheets and eat like a sane person: Breakfast: Egg McMuffin, bagel with cream cheese: 610 cal Lunch: Grilled chicken sandwhich with small fries and 3 packets of ketchup: 670 cal Dinner: McDouble burger and 6pc chicken nuggets with sweet and sour sauce: 690 cal That's a 1970 calorie day, which leaves plenty of room in the adult male calorie budget for a cappuccino or something else here and there without breaking the bank. The problem with people is that they don't do the mental math, or cheat at it, and have grossly incorrect perceptions of how much energy they are consuming in everyday meal items and portion sizes. Following the types of meals described above, I've lost over 20 lbs. in the past couple months by eating almost entirely at McDonald's, Wendy's and a few other chains.