HBP - You're right, we do have less rights than factory workers. If Health and Safety rules were applied to flying as they are in offices and factories all over the country then we'd never get off the ground!
I've never seen anything in print related to crew breaks during a duty. In my (limited) experience you're relying on your captain being strong enough to stand up and say "That's it, we're taking 5 or 10 mins out to eat"
As you say, unfortunately not everyone feels able to do this. Combined with the fact that sometimes we can eat up front during the flight and you can't, all you can do is stress the point to the captain that you really need a few minutes rest and some food. If this doesn't work then put something in your trip report and make sure your colleagues do the same. If still nothing then do you have a union?