I never thought about it, but I'm demand feeding (not co-sleeping though so I don't know if that would make it harder), but DS at 6 months is now sleeping from 7pm-9am with a feed at anywhere between 9pm-11pm (well, this may not qualify as demand...I go in and feed him) and between 6:30am-7am (when he "demands") and we never did any "training"....but I do eat a decent amount of protein at each meal (but not too much as I'm doing Weight Watchers at the moment - so it's pretty healthy protein and reasonable serving sizes). I don't know if this qualifies for sleeping through, but I think it's pretty good. Oh - and this is true most nights of late...but not all...last night was not fun at 4am.

You may be on to something.