Hubby is a 25-year+ renal transplant recipient and recent cancer survivor, and I have my own "stuff," and neither of us has big healthcare bucks -- so we're being really careful as regards nutrition:
We avoid canned tuna. Fresh (or frozen only on the boat), wild -- not farmed -- is best. Sure, it costs more, but smaller portions go a longer way toward nutrition. And we only buy from local, trusted fishmongers.
(Well ... my hubby ... as I'm allergic to most kinds of fish.)
Maybe it's just a crapshoot, but we figure what we spend on good nutrition is savings toward future medical expenses.