Redout,
if it's any help, the Medical Branch veiw the consequences of "underweight" as seriously as they do "overweight". The 2 problems aren't a million miles apart in the consequences that may occur with the body.
I would respectfully suggest that your friend contacts the Medical Branch to discuss the problem, they are very approachable and proactive, and will do their level best to help with any problem.
In my experience, if they can't make a suggestion to resolve a particular problem, they'll be able to put you in touch with someone who can.
Hope that helps.