if there's more than one head of household, more than one fetch job can be genereated to replenish consumed food.

Example: In a full Cottage 3 apples are consumed, but both heads of household will go to each fetch 3 apples. This makes a total of 6 which are also counted in the food statistics.
The Cottage doesn't seem to consume less to compensate for the fetched surplus in all cases. Sometimes it works, sometimes not.

Workaround: Instead of the intended 1 food per villager overproduce food by around 1.5 per villager.

Nevermind, fixed it myself with a mod. Turns out the modding feature is also fun.