Question: I'm a 5'4" runner in middle school and recently struggled with being both underweight and obsessed with training. At one point I was only 88 pounds. I recently came down with an injury dealing with a weak hip abductor and sciatic-like symptoms and I haven't run in a month. I am now working on gaining weight, but how can I gain the right type of weight since I am not running. Any advice?

Answer:

First of all, it's great that you are asking for advice, rather than adopting the idea that you can eat anything that you want. The basic principle of gaining weight is that you need to ingest more calories than you burn. Since you are still growing, your caloric demand is greater than that of an adult who is the same size. You need to eat a well-balanced diet consisting of carbohydrates, proteins and fats. Fats are the most calorie dense of these foods. In addition to your regular meals, eat healthy snacks. Nut butters (peanut butter, almond butter, etc.), nuts, avocados and similar calorie dense foods have healthy unsaturated fats and a lot of calories. You should have no problems ingesting enough protein with a balanced diet; most American diets have well over the recommended daily intake.
Make sure that you rehabilitate your injury. Weakness of the hip abductor muscles is a very common issue for runners. While recovering from your injury don't just work on hip and core strength but start performing leg and upper extremity exercises too. The stronger you are, the more resistant to injuries you will become. 
Good luck.
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