In my hometown, it seemed like the size of the average congregant grew in proportion to how strict their denomination/pastor/sect was about other appearance issues. The most conservative one in the area was the Pentecostal Holiness church. The women did the jean jumpers (no denim on Sunday, though) and long hair thing, the guys almost always wore suits, and they were generally the biggest weight-wise. 

This weight phenomenon was easily observable, since my family ran one of those fried-food-palace family restaurants, the only one in town. Even if you'd never been a church brat like I was, if you worked many Sunday mornings, you got to know who belonged to which church pretty quickly; they were all regulars, and the rush came in waves according to which church ended when. Of course, you also quickly learned to hate that shift, as the church crowd was largely made up of awful tippers (And the Lord spoketh unto them, "Tracts are not tips, y'all!") who had little patience and were happy to let their kids burn off all that sitting-still-all-morning energy while they "fellowshipped" from table to table. Hehe, can you tell I'm still recovering from both Pentecostalism and waitressing?  

The hypocrisy used to drive my poor dad nuts. He'd get looked down on for leaving church as soon as it ended or before it did if there was a long altar call. He'd race to the restaurant (smoking on the way) to get it ready for the rush, then work his ass off to make it all run smoothly while trying to seat 12 and 15 people to a table. And then, some churchy person would stop him on their way back to the buffet for the fourth time to say something like, "You know, this is the Sabbath. You shouldn't be open on Sundays. Oh, and are you bringing any more fried chicken out? Someone just brought a pan out but Brother So-and-so took all the drumsticks. Mac and cheese is gone too." Dad took it in stride, though. Sometimes he'd just say "Aaah, sorry but nope. We're not bringing out any more chicken, ever. You missed the last pan." Or, no lie, he'd pull a genuine rubber chicken out of the designated hiding spot, pop it in a pan, and hand it to the baffled customer. He had no qualms about keeping kids in line, or occasionally asking a big party to free up the table they'd been chatting at for three hours. Dad still keeps me sane, in a lot of ways. 

Heh, sorry for getting all story time on ya. Kinda swerved off onto Memory Lane there for a minute.