Increasing Fibre Requirement in MFP App

Hi all,

Having a need to ensure my digestive system operates well I take particular note of my fibre intake through MFP. I'm 61 years old and I managed to lose 50 plus pounds in a six month period using MFP as a way of balancing my diet/exercise regime. During that period I, like most I would think, set my fibre intake at 30g per day, and have always planned my diet to accommodate that. With recent updates to the app I've noticed that even though I have a fibre intake of say 32g, on doing some exercise (a walk burning 350 calories for instance) my daily requirement goes up to 38g. It seems the more exercise I do, the more fibre I need! Is that correct ? If so why ? Can anyone explain it, and keep it simple, I'm just an old bloke. Thanks in anticipation.

Smudge