I'm a 23 year old female and i weigh around 138 lbs if i drink three ensures or nutriments a day will that help me gain weight ?

Probably, but why?: For a woman in her twenties, 138 lbs sounds normal (but that depends on her height, and what she has been weighing over the past 12 months). In general, we doctors like to do things the natural way, meaning we prefer weight gain by eating nutritious foods that are part of a balanced diet. Balanced means a good variety of foods. Ensure comes in a can, but if needed, it will increase one's weight.