The Beracha of "Boreh Nefashot" is recited after eating fruits that are not among the seven special species of Eretz Yisrael, after eating vegetables or foods that are not produced from the ground (such as meat, eggs and cheese), and after drinking beverages other than wine. Whereas other foods require the longer Beracha of "Me’en Shalosh" (such as "Al Ha’mihya" after eating certain grain products, and "Al Ha’etz" after eating fruits from the seven species), these foods require the briefer, generic blessing of "Boreh Nefashot."
The question was asked whether "Boreh Nefashot" can fulfill one’s obligation after eating foods requiring "Me’en Shalosh." For example, if a person does not have access to a Siddur and does not know the text of "Me’en Shalosh" from memory, should he recite "Boreh Nefashot" instead? And if somebody mistakenly recited "Boreh Nefashot" instead of "Me’en Shalosh," has he fulfilled his obligation after the fact?
Hacham Ovadia Yosef addresses this question in Hazon Ovadia – Berachot (p. 120, in a footnote), and among the sources he cites is a passage from the writings of the Rama Mi’Pano (Rav Menahem Azarya of Fano, Italy, 1548-1620). The Rama Mi’Pano seeks to explain why the Talmud, on several occasions, uses the phrase "do nothing" ("Ve’lo Kelum") in reference to situations where "Boreh Nefashot" is cited. Instead of stating that a person in this situation recites "Boreh Nefashot," the Talmud says he "does nothing." It seems strange, at first glance, that reciting this blessing would be described as "doing nothing." Many commentators explain that the Beracha of "Boreh Nefashot" was initially enacted as a voluntary blessing, and thus somebody who ate a product that does not require "Me’en Shalosh" was, indeed, not required to do anything. (Over the generations, this blessing was accepted as mandatory, and so nowadays it is strictly required.) The Rama Mi’Pano, however, suggests a novel interpretation, explaining that this description refers to the contrast between "Boreh Nefashot" and the Beracha of "She’ha’kol" which is recited before eating foods that do not originate from the ground (and before drinking beverages other than wine). "She’ha’kol" is a generic blessing which covers all foods; if one recited "She’ha’kol" before eating any food, even a food that requires a more specific Beracha, he has, after the fact, fulfilled his obligation. By contrast, the Rama Mi’Pano writes, "Boreh Nefashot" is limited, and covers only those foods for which it was instituted, and for this reason it is described as "nothing."
According to the Rama Mi’Pano, then, the recitation of "Boreh Nefashot" does not suffice for foods requiring "Me’en Shalosh." Hacham Ovadia cites numerous other Poskim who concur (including the Ma’amar Mordechi and the Peri Megadim). Although some Poskim (the Ginat Veradim and Kaf Ha’haim) rule differently, and maintain that one who must recite a "Me’en Shalosh" fulfills his obligation by reciting "Boreh Nefashot," Hacham Ovadia concludes that this should not be done, since many Poskim ruled that "Boreh Nefashot" is ineffective when "Me’en Shalosh" is required. Therefore, if one does not have a Siddur and is thus unable to recite "Me’en Shalosh," he should not recite "Boreh Nefashot," as this Beracha would be recited in vain according to many Poskim. Rav Moshe Feinstein (1895-1986), as Hacham Ovadia cites, ruled that one should recite "Boreh Nefashot" in such a case, but Hacham Ovadia respectfully disagrees, noting that doing so runs the risk of reciting a Beracha in vain.
However, if one mistakenly recited "Boreh Nefashot" when "Me’en Shalosh" was required, he should not then recite "Me’en Shalosh," given the view that he has, after the fact, fulfilled his obligation.
Summary: If one ate a food requiring the Beracha of "Me’en Shalosh" ("Al Ha’mihya," "Al Ha’etz" or "Al Ha’gefen"), but he does not have a Siddur and does not know the text by heart, he cannot fulfill his obligation by reciting "Boreh Nefashot" instead. However, if one mistakenly did recite "Boreh Nefashot" instead of "Me’en Shalosh," he does not then recite "Me’en Shalosh."
