Lupin always being sickly

[severusbook4]

No: HPFGUIDX 77967

Sorry if this has already been asked.

    Lupin is always descibed as being a little worse for wear, or 
unhealthy.  Do you think this is a result of not feeding on humans 
at every full moon?  Or a result of the serious potion he has to 
take?  

     If it's the lack of fresh meat, I say the MOM should feed 
Umbridge to him if it would help build his strength.

Severus