That was some refreshing science.
I don't doubt in either case that the human body would be capable of surviving at such drastic sizes. And, in the Ant-Man film's case, they did not let the audience forget that the Pym Particles and size-shifting have side effects that affected the brain. There is also the two fairly gruesome deaths as a result of the imperfect shrinking process. Thinking about it still gives me chills.