Originally Answered: How do I gain weight quickly?
Eat lots of carbs and high calorie foods, but maintain a good exercise routine otherwise you'll wind up with a lot of blubber instead of the good kind of weight, i.e. muscle. Eat pasta, rice, bread, lots of dairy, chicken, fish, and on occasion red meat (cut out processed meats, they're bad for you), along with fruits and vegetables. WORK OUT BY LIFTING WEIGHTS!! After workout, drink a protein shake. They sell good ready-made ones at Walgreens in the health section called Myoplex. The shake must be consumed 30 minutes post workout or else your time in the gym was for naught. Stay off junk food like potato chips, cookies, cakes, sweets, twinkies, chocolate, and definitely stay off soda. these foods have absolutely 0 nutritional value and severly damage your body further down the road. Ignore the idiots who advised you to eat at McDonalds and to eat junk food. They're probably lugging around rolls of belly fat right now.
Keep this routine consistent and you will see results in a few short weeks.