As with most preserved meats, Spam is well-loaded with the notorious preservative Sodium Nitrite. Tastes like salt, so hides well in meats: hams, sausages, "cold-cuts", luncheon meats, both canned and otherwise.
Today, processes are used to preserve meats without nitrites; there are none in canned fish, other canned meats, like poultry, but as far as I know, Spam and its brother "Treet" are still nitrited. Sealed packages of meat products are not even refrigerated, being vacuum-sealed, and probably irradiated, killing everything tiny living in the product. AFAIK, labeling does not require irradiation mention.
Not afraid of nitrites? Well, if I live to be Lon's present age, I'll then eat anything and everything, especially if I can get to look like him! Nitrites are metabolized by the human body to nitrosamines, well-known carcinogenic compounds. imp