Are the sex scenes in this film real??

Actually, much has been written about how the scenes were indeed real and a little googling you can find interviews with the director and the actress. The best one is (google) "stumped magazine anapola mushkadiz" to bring you to the link.

To summarize all the interviews, the actors were amateurs and this was their first and only film (Ana actually did a couple small amateur projects afterward but they sound more like home videos). Ana and Marcos used their real names in the film as an aid. Marcos worked in some Mexican government office. Never found out what Ana did prior but she wasn't an actress but she was referred to the director by a friend and was selected because she looked younger than her actual age. They weren’t given scripts and were instead told what to do from scene to scene.

Ana and Marcos spent a lot of time with the director prior to the shoot just getting to know each other. They knew there would be sex scenes. Ana never considered the sex scenes to be real because they never reached a climax. I have to wonder what was wrong with Marcos, Ana is gorgeous, who would have that much control? There's not that much on Marcos.

There was great controversy at the time because some thought that because they were amateurs they were exploited, but the actors stated they had no problem with the scenes. Ana was already very comfortable with nudity. In interviews both seem to have quite liberal views on nudity and sex in film and despite the intensity the characters had to show in reality they found the experience to be positive. In fact, Ana adored her director to the point where I have a feeling she had a crush on him.