Well, this is at least from the Ultimate version..And Wikipedia:
According to Ultimate Fantastic Four #7, Ultimate Reed's body has been radically transformed, and his only internal organ is a "bacterial stack" that generates energy (presumably from air) to fuel his body. This obviates the need to explain, for example, how his circulatory system can pump his blood when his body is stretched the length of a football field; he simply has none. Lacking a digestive system, he has no need to eat or drink. Similarly, because he has no lungs, Ultimate Reed doesn't need to breathe in any conventional human sense and can survive in environments lacking oxygen; however, during his time in the N-Zone, where the atmosphere is essentially acid, he is unable to breath the air there, suggesting that he still requires air to a certain degree.