Seriously? for someone who has read up on bowels for so long, your grasp of the alimentary canal is startlingly bad Toby
Food can be in your stomach for about 5 hours (maybe more), then it passes through the small intestine, in another say 2 hours, 40 hours travelling through the colon....maybe more maybe less. Basically, food can take between 24 -72 hours (according to most sources) to be ready to come out the other end. If you are constipated though it could be backed up a bit anyway, and be even longer as it 'queues up'. So, fibre eaten today might start having an effect in 3 or so days ! BY the way, totally non-medical assessement made by me then about 3 or 4 days, just going by my own observations. Oh and one banana and a portion of peas isn't enough in one day anyway.....its a start.....but not enough....