Thanks for chiming in!
Your followers continuously consume food and herbs, as long as the resources are available.
When they lack food, they start to lose health (life points). When they lack herbs, they get ill (which might explain why sometimes the whole village goes ill: there are no herbs left in storage).
This is what the nutrition and hygiene systems are about.
You can read individual nutrition/hygiene info on the character sheet.
Hope it's clear!