Re: the OP's question.
You should also make sure that whatever you register is in the common english vernacular if you're registering .com.
Your example "loss-weight" doesn't make sense with commonly used english language. So, that would not be a good name to register, whereas "weight-loss" would.
Also, just like owntype mentioned... when registering hyphenated domains, you will need to find keywords that are highly searched for. While 10,000 exact searches per month may be acceptable results for some non-hyphenated keyword domains, you will have a better chance of selling a hyphenated domain if it has much more, IMO.