I know someone who gets them about once a year. It can be genetic, and has a higher incidence in men.

I just learned (or read, at least) the other day that spinach can cause them, I imagine other foods as well.

Intriguing. Spinach and other dark leafy greens are also goitrogenic (can contribute to goiters). I wonder if there is a correlation.

Do note: eating massive amounts of spinach is unlikely to cause a goiter or kidney stones if you are not already susceptible to them.