It's ironic how much the weight losers and the weight gainers have in common. Both are frustrated by a seeming inability to change their bodies. Both like to blame it on their genes. But do you know what the biggest irony is? They both make the same mistake (sort of) -- wannabe weight losers eat too much of the wrong things, and wannabe weight gainers just eat too little.
Way too little. WAY too little. Period. (And often they eat the wrong things too, just to compound the problem. Milk shakes and fried foods are not the answer.) According to Dr. Susan Kleiner in her book Power Eating (p. 243), for a serious resistance-training and weight gain program, a man needs 24-28 calories per pound each day, while a woman may be able to start gaining at around 20 calories per pound. That's a lot more food than most skinny people even consider eating!
Why so much? In a word, metabolism. A lot of those calories are being burned to fuel the muscle building process, which also uses calories. Think about your car; it takes more gas to accelerate your car to 80mph than it does to cruise at 80... a lot more. In the same way, it takes a lot more calories to gain 20 or 30 lbs of muscle than it does to maintain it after you've got it.
Failure to eat enough is the first mistake. The second is not eating frequently enough. If you're trying to gain weight, it's better to eat five or six small meals than three big ones. When I managed to put on 15 lbs in 10 weeks, I was eating eight times a day! Not only that, but I ate different types of meals at different times. That may require a bit of explanation.
- Before the workout, you need to get a lot of energy into your muscles so they can handle a good workout, so you go for things that digest easily. That generally means no meats, although eggs are ok (forget the Rocky bit and cook them!), as is cheese. Make sure you have 60-90 minutes for these meals to digest.
- Right after a workout, your metabolism is going crazy! For about 30 minutes, it's a case of the quicker you get food in, the faster your muscles rebuild. So for those meals, I focused on foods that digested quickly -- which again means you skip meats, which digest slowly. You go for protein shakes, fruits, yogurt, and such.
- Maybe an hour after your workout, you can start thinking about heavier things. (Yes, now meat's on the menu!) You've got all night for your body to finish utilizing all those calories.
There was one thing I did that I would do differently now, and that's going extremely lowfat. I made a real effort to keep my fat calories between 10% and 15% of the total, and it made it very difficult to eat the necessary number of calories because of the volume of food I needed. Eventually I instituted a "cheat day" every weekend, where I would eat anything I wanted, no matter how "bad" it was... and I mean ANYTHING! I distinctly remember one Saturday where I bought a chocolate milkshake at Baskin Robbins, which I drank at Pizza Hut along with the supreme pan pizza I ordered. Even with that kind of cheating, I still didn't gain a single inch around my waist during the 10 weeks. I got to where I dreaded eating, and that's why I finally stopped gaining. I simply quit trying to gain.
If I was doing it now, I would let my daily fat calories equal 25%, even 30% of my total AS LONG AS the fat came from monounsaturated fats like olive oil. I've heard that the Mediterranean Diet, which is considered an extremely healthy way to eat, can contain as much as 40% because so much of the fat comes from olives and olive oil. (You can find more info on the diet here and here, if you're interested.) At any rate, allowing a bit more fat than I did could make it easier to satisfy your calorie needs.
In addition, if you decide to try the Charles Atlas approach (I was doing a weight program) and do no more exercise than you can recover from in a single day -- which means you work out each day -- you won't need to eat nearly as many calories a day. I would review this post and try using the "active" recommendations to gain weight with an Atlas-style program. You'll be eating around 20% less calories a day that way, so it might be easier to gain eating less fat, like I did.
Those are the major things you weight gainers need to know. If you need more info, just check the book recommendation post for some ideas.