Dr. Nelson, I need to gain weight, I'm 20 yrs old, 5'4' and only 90lbs. I want to gain at least 10-15 lbs. Everyone in my family is thin but we eat healthy. How do I gain weight the fastest way? I also want to learn to maintain it after I gain. It's so hard to find any information on gaining weight, there should be more stuff available.

It is good that you want to gain weight, as you are currently underweight and gaining just 15 pounds will put you into the healthy weight range which will benefit you long term. It is certainly understandable that you would want to do this as quickly as possible, but please keep in mind that just as with losing weight, you must gain the weight slowly in order to maintain it for a lifetime.

I would recommend that you first adapt your eating habits slowly to include greater than three meals each day—five to six smaller sized meals would be great. Alternatively, you could include a substantial snack in between the three usual meals. In order to gain weight effectively, increase your daily caloric intake by 250 calories each day. I would recommend that you try to get some of your additional calories from calorie- and protein-dense supplement drinks as well as various milk-and yogurt-shakes. These drinks and shakes will provide substantial additional calories while not filling you up as much or for as long as a large meal might.

I would also recommend that you participate in strength training. This type of exercise can help to stimulate appetite in underweight individuals and it will also help you to gain muscle mass, which ideally should comprise the majority of the weight you gain.