okay thats why we have to take a billion supplements a day lol kids bodies are different then adults they're still growing yes cut out processed foods and junk but there maybe a bigger reason why he is underweight like overactive metabolism or something that isn't related to food. I'm just saying maybe you should talk to a Kids DR. before you do it ask what they think??? it's selfish if you just assume its okay... Teens would be fine but not children!!!!