Hello i am 18 y/o 87 lbs and female. what's the best health guide to gain weight possibly a month or 3-4 months. i want gain up to 15 pounds. thank yo?

Caloric supplements: Try adding carnation instant breakfast to whole milk. Other options include boost, ensure or the "plus" version of either. Eating energy dense healthy foods such as nuts or nut butters will also help. Aim for 2-4 lbs per month as reasonable goal.

Why, then how: I encourage you to work with your doctor, nutritionist in that office, and a personal trainer rather than any off-the-shelf plan. Share with your doc and team the why about wanting to gain weight and where (on the body) you want to see changes. Body weight is just a number affected by many factors (e.g., bone, muscle, water, fat, etc.). Sharing 'why' will lead to a healthy plan.