much harder going up than down...
No, it is just the opposite problem. Guys that have a hard time gaining weight just don't normally eat enough calories to grow given their metabolism. A lot of bodybuilders started out really small, but if you keep piling on the calories, you will put on weight. I have to diet really strict to lose weight, but when I do, I lose it quick (77 pounds so far since September). When I am not dieting, I gain just as fast (about 120lbs in a year and a half). My calorie swing is really wide, and the math supports both situations. I am currently eating about 1800 calories a day, and that translates into about 3 lost pounds a week, and I can push that to 4 or 5 with exercise. When I am not dieting, I probably eat around 8 to 10,000 calories a day if I eat out a lot, which explains the rapid weight gain. The fun part is that I can put on a ridiculous amount of muscle if I lift heavy while I eat heavy. Quite a few years ago, I went from 225 to 365 on bench press in about 3 months. That was fun.
I am still at about 190lbs of lean body weight, but it is unfortunately still well padded at 280 lbs. I am pushing to hit 220 in 12 weeks, but I need to get my lazy ass back in the gym since I won't make it at 3lbs a week.
Most people who are really fat just normally put down a lot of calories, and most thin people do not. If you put in some big calories, you will gain a lot of size over time. Most "hard gainers" that I know usually put away up to 10,000 calories a day to gain size. Natural for us fatties, but a challenge for you smaller guys.
It is always good to know how many calories are in restaurant food. If you are prone to gaining weight, you will almost always choose to eat more than enough calories, but it is easier to make better choices if you have good information.