This is kinda picking nits, but it seems to me that it would be more accurate to weigh meat before cooking, if you wanted to get the protein measured really accurately. Assuming the stats for raw meat are available.
What set me thinking about this was seeing sirloin on the list. I like my sirloin VERY rare, aka “blue.” Ideally, I cook the outside for just a minute or two per side on charcoal or a hot skillet, so more than half of the interior is literally still raw. In contrast, my spousal critter likes her steaks medium-rare to medium (she likes the taste and texture of medium-rare better, but is squeamish about the appearance of it when it’s still that red). When I cook it a sirloin to medium, it shrinks a lot, due mostly to water loss from the heat and especially from contraction of protein structures, which pushes a lot of water out. So, if I weighed her steak after cooking, it would be lighter but would not have lost any significant amount of protein. (OK, the liquid that is pushed out is not pure water: it’s red because it contains myoglobin and doubtless contains other soluble proteins. My guess is that this is not TOO significant, but IDK for sure.) Weigh both of our steaks after cooking, and you would overestimate the protein I got or underestimate the protein she got.
For fatty meats, cooking will render some of the fat out, so unless you collect that fat and make gravy or something (and eat all of it) longer cooking will probably throw off your fat macro calculation a bit, too. In that case, nutrition information for cooked meat would be more accurate, I guess.
Since it’s not such a great idea to eat pork or chicken rare, they may be less error-prone, although I would argue that either is nicer to eat when just barely cooked enough for safety (by which I guess I mean a little less than most people would think was ideal) rather than really getting them well-done and dried out.
Whether this level of concern for accuracy matters is up to you. I certainly don’t track anything that carefully!
