If you have a few 100 people in an area literally spending their waking hours worrying about having enough food. Areas without enough of the right nutrients are pretty common. People are pretty good at figuring out what makes them feel better/healthier.
Some places are iron poor, some even resort to eating dirt, especially when pregnant when you need more iron. Some areas are salt poor and animals will go to extreme measures to get to salt. Some areas have poor bioavailability and require crushing, special cooking, soaking, or a narrow range of acidity to be available, which of course becomes the norm for cooking in those areas. Some even become religious standards, things like fish on fridays or avoiding pork (before trichinosis was controlled).
Some places are iron poor, some even resort to eating dirt, especially when pregnant when you need more iron. Some areas are salt poor and animals will go to extreme measures to get to salt. Some areas have poor bioavailability and require crushing, special cooking, soaking, or a narrow range of acidity to be available, which of course becomes the norm for cooking in those areas. Some even become religious standards, things like fish on fridays or avoiding pork (before trichinosis was controlled).