My weight is 53 kilos and height is 6 feet. i want to gain weight.my diet is perfect.i don't know why am i so skinny.what's the reason? please help me

See Dr., then eat...: If one is truly underweight (based on height, family background, and body type), a Dr. can evaluate for a hormonal, digestive, or other disorder. If no medical cause is found, then one can add weight by eating more calories of nutritious foods, while also doing weight-training to increase muscle. Proteins: egg white, chicken breast, salmon, ... Better fats: olive oil, peanuts, almonds, tofu, ....