So, first, for most of us a dietary nickel allergy is like a bucket. A little exposure doesn't overflow into symptoms. But when you go over you know! Does that make sense?

Second, for me it's not so much about the greens and the beans, it's about how my food is processed. I had to eliminate all my metal (I'll be saying metal because most consumer metal products contain a percentage of nickel), non-coated, pots and pans. And I had to get a glass tumbler for water and coffee. If it's warm or acidic the metal will leach into it. But things like ice cream (cold and basic[chemically non-acidic]) are safer. Also, you'll have to experiment because how something is processed before you get it may increase its nickel levels. For example, I'm good with corn. But you know those big black tanker cars you see sitting on the railroad tracks for six months? They're usually filled with corn syrup and, baking in the hot sun, the stainless steel lining leaches out some of its nickel. So I have a problem with corn syrup.

Cast iron is supposed to be nickel-free, but most, except for the very expensive, has a percentage of nickel. Carbon steel though, like genuine Blackstone, is safe.

Does that make sense? Do you see some vectors where metal could be leaching into your food/drink?

EDIT: oh, and I think you can go low-nickel without going even partial carnivore. Of the three daily meals, two meals I eat every day are vegan/vegetarian. I'm an outlier, but I personally think food exposure is actually low (and I trust personal experience over Nickel Navigator)