In a recent SVN update the Meat Packing Plant was set to replace the Butchery.
The meat packing planet give +5 food.
The Butcher gives +1 food and +1 for having each of deer, cow, pig, sheep, and poultry for as max of +6.
So that does not directly explain a loss of anything more than 1.
However, they both give the raw meat resource. Perhaps the "real effects" text sees that the replaced building gives the free bonus and calculates the loss of output for any building that requires that resource but does not add them back in due to the meat packing plant also providing the resource (it might, for example, check for a new free resource and find that the meat packing plant's free resource is one you already have and therefore does nothing for it, but not check that the replaced building's free bonus is also replaced and therefore adjust for the presumed loss). There are a few other buildings that require that resource (like the sausage shop, for example) so the -11 might be counting them all as being deactivated due to the supposed loss of the required bonus.
So the question is: if you build it do you really lose that much food per turn or is it just an "actual effects" calculation/text problem?