Just had another thought about this with the formula milk - they seem to have different 'levels' of milk, like stage 1,2,3 etc for when baby grows (not sure if all brands are like this, but the ones I have used in the past are). I presume they alter the formula slightly for different needs as baby grows. I wonder if giving the wrong 'stage' of formula milk might contribute somehow? Like if they have a stage higher than they are ready for it might contain too much fat and this could affect baby somehow?
Just a thought, again I'm not suggesting this is the case but it might make sense?
I quite like this thread, it seems to be quite a nice discussion on the topic without being too biased one way or the other