I eat at McDonald's five times a week, since there is one an eighth mile away from my work. I also am 5' 7" tall, and weigh in at usually 125-130 pounds. My fat percentage is 6%.
Here is the kicker, though: I have a very, VERY fast metabolism. Today I ate at McDonald's the new Angus beef 1/3 pound burger meal (It is really good!) at 11:00 am. By 2:00 pm I was already hungry again. I usually walk about 5-7 miles each day just doing the normal work routine, and I have a very long and quick stride, so much so I can usually out pace people a foot taller than me.
During the week, in order to maintain my level of energy, I have take in about 2500-3000 calories, and that is not an exaggeration. But, on the weekends, that gets cut in half, since I am relaxed. I eat my usual breakfast (yogurt, cereal) at around 6:30 am, then I am not hungry until noon. I "tough it out" until about two pm, and then eat lunch. After that, I do not eat until the following morning. So in a sense, I self regulate my intake according to demand.
Now, before anyone starts pontificating about eating me fast food, and how bad it is for you, I come from a family with genetic heart disease. It does not matter if I eat healthy or poorly; eventually I, like everyone else in my family, will have to have open heart surgery. There is no argument you can offer, I have received opinions from several doctors on this. It is just a fact of my life.