If it was posted after you joined the group, it should have come in your email. Right now, however, Yahoo is having an issue and not all the mails are coming to peoples email. This should be fixed shortly.

The surest way you can find it is to go to
http://health.groups.yahoo.com/group/radiantbreakfast/messages
and then search through the messages to find the first one with that subject.

Hope that helps,
Kitty