How to gain weight?

Well, if you want to gain weight naturally... I would eat well, (don't try to eat junk food, it doesn't work) and exercise! (not too much exercising, just enough to keep you healthy) You can check a food guide to see serving sizes, and put it all together in a meal. That's all I can suggest!

Foods high and protein and plenty of fiber will assist you. If you weighed 120 pounds you would need 150 to 200 grams of protein a day to gain weight. Muscle weight also weighs more than fat. Add some weight lifting to your new diet.

Take in two protien shakes a day.
boiled eggs, walnuts, cashews, almonds, avacado, tuna, beef, chicken, apples, bananas and more. Keep junk food out of your diet.