Should my bf take Reta?

My bf keeps telling me he wants to hop on Reta but he’s genuinley already so so skinny, he’s 5’10-5’11 and he’s about 155lbs and he hasn’t worked out in a while but he’s a very good athlete and he’s playing a sport year round. He is starting to get back into the gym, is it a good idea he wants to get “lean” even tho he already is…