Hello ismael. Thanx for using hcm.To gain weight first thing you have to correct is your digestion and absorption related issues.Many patients suffer from frequent bowel habits.This has to be corrected. Coming to diet and nutrition, consume more of carbohydrates along with proteins which helps in increasing muscle and weight too.Carbohydrates like cereals rice, chapathi, breads, oats, multi grain cereals . Proteins like chicken without skin, lean meats, fish, eggs.consume small meals rather than big 3 meals. Include dairy products , milk shakes,Cheese, nuts in your diet.limit intake of butter , cream , ghee as it makes you put on weight but makes your cholesterol bad.