How does a super fit person get kidney stones? You eat well, live clean and exercise regularly.
Well, if you eat spinach in your smoothie every day for three years, this can totally happen.
Spinach is high in oxalates and oxalates are consistent with the formation of one type of kidney stone. The oxalates also have great binding power not only to form stones, but to bind to the other minerals in your diet like iron.
Take away is spinach is okay, but get some variety. If one week you pick up a bin of spinach to enjoy, next week get one of arugula instead. Variety.
Kidney stones, or nephrolithiasis formation are influenced by both environmental (dietary) and genetic factors.
Beyond diet, the microbiome does play a role in the absorption and secretion of oxalates.
Humans don’t have the enzymes to break down oxalates. However, microbes in your gut do. The presence of a naturally occurring oxalate degrading bacteria, Oxalobacter formigenes (Oxf) certain strains of Lactobacillus and Bifidobacterium help reduce oxalate absorption.
It is more than just this handful of bacteria that do the job. A balanced microbiome with broad diversity of healthy species is what tends to help the most
Oxalate crystals are sharp and pointy and potential to irritate tissues all over the body. They could be one of your root causes for chronic pain.
 Mehta, M., Goldfarb, D. S., & Nazzal, L. (2016). The role of the microbiome in kidney stone formation. International journal of surgery (London, England), 36(Pt D), 607–612. https://doi.org/10.1016/j.ijsu.2016.11.024