The meat is the whole abdomen of a radroach. Since radroaches appear less frequently Fallout: New Vegas than in Fallout 3, radroach meat is increasingly difficult to find. The effects of the radroach meat in Fallout: New Vegas is notably different: it restores a small amount of hit points, but gives an unreasonably high dose of radiation. Consuming it also gives a -1 penalty to Strength. Needless to say, it may be better to avoid this snack altogether than try to consume it.
Within the game files exists a version of radroach meat, that gives 18 rads instead of the normal 10. It was supposed to be dropped by the irradiated radroach, but after cutting the creature, the other variant of the meat was cut as well.