It's certainly not helping to have all the free stuff around, but I'm guessing no-one's holding a gun to heads to make the employees eat it, and HR is probably not inspecting brief cases at the door to make sure employees aren't bringing in apples and salads.

Forget HR. That's not going to work. Make friends with the owner's wife and share your concerns with her (sexist assumption here; works the other way if that's the case). Or whomever the caring spouse of the most senior fat person is. As the employees age (which is happening in my company), you'll see more and more interest in better health, but it will come from the older employees, not HR.

I think many of these conditions are possible for us all, and hence genetic in a way. But the switches are turned on or off by conditions such as diet and weight.