My son is 14 and is a distance runner. Over the last month he's been runing about 8 miles a day. He's about 5'6" and about 100 pounds. He's lost weight and is now around 94 pounds. We do feed him a high carb diet and his appetite is voracious. I was thinking about some of those weight gain powders at GNC for additional calories. I have no idea if this is the right direction to go. It just doesn't seem good for a kid as skinny as him to be losing weight.
i kinda agree with Tex, but really your boy just needs to eat as much as he can right now. I'd say more good fats, if he likes avocados & seeds/nuts get that into his system (e.g. on sandwiches for avocado, or pistachios or sunflower seeds for munching on). I can eat pistachios, mixed nuts, sunflowers forever... just try to get the unsalted or low salt sunflower seeds
I'm doing about 8-10 miles a day myself. I'm 30 and have nowhere near his metabolism, but I was at a point where I was getting too skinny too and I just added alot of peanutbutter in with my regular diet and now I'm still leaning slowly and building alot of lean mass in a short time. Might work for him. It;s high cal good fat. Be sure to use peanutbutter with no hydroginated oils. Eggwhites work too!