The Talmud states that one who steals wheat, grinds it, bakes it, and eats it, if he also recites a berakhah, this is no berakhah but rather is an act of blasphemy. Rishonim debate which “berakhah” is being refered to. According to the Rambam (Hil. Berakhot 1:19) one who is eating any prohibited food recites no berakhah, before or after. The Ra’avad argues, understanding the intent to be that there is no zimun, because prohibited food has no importance or k’viut. This is also the opinion of Tosafot (Berakhot 45a, sv, akhal). The Meiri expresses a third view, that the berakhah refered too is the birkat hamitzvah of separating chalah.

The Rosh, Berakhot 7:2, challenges the Rambam based on the language of the Talmud, which implies that a berakhah is recited, although it is blasphemous. The Ohr HaYashar to Bava Kama asserts that the Rambam possessed an emended text. The Even HaEzel suggests that the Rambam’s position is actually not based on the above passage; rather, it is founded on his belief that prohibited food is not considered benefit, and is by its essence removed from the concept of berakhot. The Resp. Panim M’eirot (II, 7) at first posits as a source for the Rambam the passage in Bekhorot (37b) that states that one who purchases food that is discovered to be prohibited is entitled to a refund even if the food has been eaten, indicating that eating prohibited food is not considered a benefit (as the Sma, C.M. 234, understands). He then notes that the suggestion is imperfect, as that passage, as codified by the Rambam, applies only to biblical prohibitions; the berakhah ruling is applied to all prohibitions. The Taz, who makes a similar suggestion, offers that berakhot is an area of special stringency, and thus even rabbinic prohibitions are excluded from benefit; the Panim M’eirot, though, considers that suggestion forced. R. Ovadiah Yosef (Ma’or Yisrael) understands it to be an enactment of the Rabbis that berakhot are only recited on kosher foods.

R. Ezra Batzri (Resp. Sha’arei Ezra, I, 13) rules that practically speaking, one who has eaten a forbidden food should not recite birkat hamazon, as a result of this dispute. Even though the rule would be that as a biblical commandment, birkat hamazon would command stringency when in doubt, that would apply when the obligation itself is clear but the circumstances are vague. In this situation, since the obligation itself is unclear, the rule of “safek berakhot l’hakel” would attach.

The Shulchan Arukh (O.C. 196 and 204) rules that one who eats prohibited foods out of medical necessity does recite a berakhah. In Beit Yosef, he does cite other views, but dismissed them, and feels that even the Rambam would agree in this instance. The Bad Kodesh (IV, 3) explains that the issue here seems to be whether the Rambam’s stance against berakhot on prohibited foods is due to the transgression (“berakhah haba’ah b’aveirah”) or the possibility that forbidden foods are not considered benefit. If the former theory is true, in this case, where no transgression is committed, a berakhah may thus be called for.

Another ramification of that question might be the issue of whether one recites birkhat hamazon after eating in an improper manner, but in a situation such that the problem is not nonkosher food but rather the procedure involved in consuming the food. The Piskei Teshuvah (38) posits this question in regard to situations such as eating without having recited a berakhah at the beginning; eating without netilat yadayim; and eating outside of a sukkah on Sukkot.