Make sure you gain it healthily.

Hi, the best way to put on weight is to increase your muscle mass. A weight training program is the first step in a gym or you can make weights yourself with an iron bar and attach 2 weights, one on each end of the bar. Pair with this changing not just the frequency and and amount of food you're taking in, but what you're taking and when. Have food in your system all the time - eat about 6 meals a day. Always have a mix of carbohydrates, protein, and a little fat at every meal. For example you can eat meat, rice and vegetables but with more meat than vegetables.

Like Nobuyuki said, excess Carbohydrates make most people gain weight. Carbs are : Sugars, corn products, wheat products, rice products, potatoes, cereals, etc. When your body burns energy, it's looking for Carbs (carbohydrates). If you eat more carbs than your metabolism needs, your body stores it as fat. If you starte eating less carbs than your body needs, then it starts using the fat for energy, and you lose weight. If you want to gain muscle weight, then eat proteins & carbs and excercise.

Come to my country and be my guest~ But before doing this, you can try eating properly. Eat snacks (they don't have to be unhealthy!) and drink fruit juices, energy drinks etc. Normally you should eat 5 times a day, 3 of them being normal meals and 2 are... how to say. Less than a meal ^^ Examples to healthy snacks can be nuts, pistachio etc, pop corn and rice snacks. You can drink milk before you sleep and maybe eat somethings at night. Carbohydrates are important but you should balance fat, protein and carbohydrates to be healthy. 3-4 cans of beer a week don't immediately give you a beer belly. I never tried to gain weight in my life, always tried to lose, and when I succeeded in doing that it was because I was able to change my habits and life style. You don't need to force yourself to eat more or eat unhealthy foods. Just change your habits to what you think is better and enjoy! Enjoy eating. There are so many foods to give you appetite. Also, eat western style breakfast and cut down on green tea. Bacon-eggs, butter and cheese, bread etc are healthier than eating rice and vegetables. Tea doesn't have any calories but fruit juices, lemonade etc have. And be careful because after 6-7 years your metabolism will get slower. Then it will be a problem to lose weight. Good luck ^^

It depends on your current situation and condition: are you underweighted or already overweighted? In general, if someone wants to get a "normal" weight, physical exercises and doing some sports regularly is recommended. Please, note that weight is an individual matter. Human organism regulates it best. If you don't want to die earlier than you have to, you'd better not play with it.