Im 5-9 160 pounds how do i gain weight fast and healthy in 1 month i want to gain 20pounds or more ?

Want more muscle?: 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, ....