How to get my son to gain weight

My 7 year old son is 46 inches tall and 43 pounds.  He seems very small for his age.  His doctor says to make sure what food he does eat is healthy...already doing that and he is still very skinny.  He only picks at his food and has to be told to eat.  Even when I serve him his favorite foods he only eats very little.  He has been tested for Celiacs disease and came back negative.  How can I get him to eat more and gain healthy weight?

[Renee Radenberg]

From your measurements, his weight is at or just above the 10th percentile and his height is between the 10-25th percentile for his age. This indicates he is normal for his age but at the lower end of the growth chart. Suggest drinking either nutrient dense drinks (in addition to eating meals) such as ensure or make your own milkshakes - yogurt, milk, and frozen fruit blended together; or milk, ice cream, and frozen fruit blended together for extra calories, protein and nutrients to help increase his weight. Recommend he has 2-3 glasses a day. Hoped this helped you.