ELI5: Why are most canned foods high in sodium? Doesn't the canning process eliminate the need for preservatives?

I'm kinda late to the party but am hoping someone will help me understand something. Your links lead to 1 cup green beans (which is a little over half of an average can) and has a sodium content of 409 mg for that site (up to 800mg for the same measurement on other sites). The link for the bread leads to a cup of crumbs which takes 3 slices of bread to create (again, depends on which reference you use, some sites say 4 slices of bread). That listing (the cup of bread crumbs) is listed as 306 mg (on other sites I am seeing 221 mg for the cup of crumbs or 123 mg for an actual average slice of white bread (which is 0.9 oz)). It doesn't make sense to me to compare these things on an oz to oz basis (especially with how different a fluid ounce and a weighed ounce can be). I keep wanting to compare them on a "how much would I eat at one meal" basis. In which case I would compare about 1/2 can green beans (between 400 to 800 mg sodium depending on reference) to a couple slices of white bread (200 to 246 mg sodium). It seems when looking at it this way the canned "meal" would be anywhere from 2 to 4 times the amount of sodium. Of course, if there's anything in between those slices of bread the sodium content will go up greatly, but I don't think that was included in the comparison point. If an individual were to change every meal of the day based off of your observation, it seems like it could be a big difference! What am I missing?

/r/explainlikeimfive Thread Parent