The minute you chomp down on a hummus-dipped baby carrot, special bacteria ninjas in your mouth go straight to work turning those nitrates into nitrites, and what a difference a letter makes. Nitrites are a natural anti-inflammatory your body stores to increase your blood flow when it's needed. This is good for your heart, of course, but some experts believe nitrites (or at least too much of them) can be carcinogenic. So what may be good for your heart could build up to levels high enough to eventually cause cancer.
The thing is, if you cook high-nitrate veggies first, that conversion happens before you eat them, and again each time you reheat them, so it might be best to stick to eating these veggies raw or at least limiting the number of times they're heated (make only what you can eat and if you do have leftovers, reheat them only once).
Other high-nitrate veggies include celery, turnips, beets, leafy greens, leeks, endive, cabbage, fennel and more.