Well first of all, 17 pounds at 13 months is not so underweight as to rasie red flags, so unless the doctor has said anything specifically about it being a big issue, I wouldn't worry too much. Sure, plenty of babies weight 25-30 lbs by a year, but there are many who don't. And, a more reliable indicator is growth charts - a baby who has been in the 5th percentile (for example) all along isn't nearly as much a concern as one who has been in the 50th and then suddenly drops to the 5th.
My neice was "underweight" from about 6 months on. Her parents just couldn't get her to eat. They tried loading her up with calories (feeding her icecream and putting lots of butter on bread and pasta, etc) but it didn't really make a difference. She just grew along her own pattern. She's now almost 8 and healthy, although quite petite.
I would hesitate to start adding in high-calorie low-nutrition foods like butter and ice cream. First, they can fill up a child who normally has a low appetite anyway and interfere with that child getting the vitamins, etc she needs. Second, while being small may be short-term, the food habits you develop now can stay with him all his life. It's better if he is in the habit of having lots of healthy, nutritionally dense foods that having high calorie foods.
If you and your doctor are concerned, ask for a referral to a child nutrition specialist. He can give you more advice on things specifically for your son' situation. But other than that, just have lots of choices available for him to eat. Do give him whole milk (that is recommended for all babies) and other foods that have fat as long as they also have other nutrients. Cheese, eggs, peanut butter, meats, etc are good for this. And always have lots of fruits available too. (Of course, go through all the steps to avoid allergies as you doctor has talked about). Don't force the issue, it only makes things harder with a picky eater. Kids won't starve themselves, just have a supply of the right foods and offer them whenever he acts hungry
Updated
Well first of all, 17 pounds at 13 months is not so underweight as to rasie red flags, so unless the doctor has said anything specifically about it being a big issue, I wouldn't worry too much. Sure, plenty of babies weight 25-30 lbs by a year, but there are many who don't. And, a more reliable indicator is growth charts - a baby who has been in the 5th percentile (for example) all along isn't nearly as much a concern as one who has been in the 50th and then suddenly drops to the 5th.
My neice was "underweight" from about 6 months on. Her parents just couldn't get her to eat. They tried loading her up with calories (feeding her icecream and putting lots of butter on bread and pasta, etc) but it didn't really make a difference. She just grew along her own pattern. She's now almost 8 and healthy, although quite petite.
I would hesitate to start adding in high-calorie low-nutrition foods like butter and ice cream. First, they can fill up a child who normally has a low appetite anyway and interfere with that child getting the vitamins, etc she needs. Second, while being small may be short-term, the food habits you develop now can stay with him all his life. It's better if he is in the habit of having lots of healthy, nutritionally dense foods that having high calorie foods.
If you and your doctor are concerned, ask for a referral to a child nutrition specialist. He can give you more advice on things specifically for your son' situation. But other than that, just have lots of choices available for him to eat. Do give him whole milk (that is recommended for all babies) and other foods that have fat as long as they also have other nutrients. Cheese, eggs, peanut butter, meats, etc are good for this. And always have lots of fruits available too. (Of course, go through all the steps to avoid allergies as you doctor has talked about). Don't force the issue, it only makes things harder with a picky eater. Kids won't starve themselves, just have a supply of the right foods and offer them whenever he acts hungry