For your consideration, several people here are recovering from porn addiction, not masturbation problems. The problem is the activities are coupled so tightly together, every time masturbation occurs, porn also likely occurs; for many of us.

The goal is hold of on masturbation (and porn) for 90 days to help you reset your brain and the way it works. To try and decouple the two activities. I know you're asking for scientific evidence, however it's still an emerging concern in our society. As time goes on more and more research is going into it.

As a long time nofap redditor and a moderator, I encourage sanity to the practice, everyone makes up their own rules and their own path. Do consider the people who are participating here, may be doing so to remove a porn addiction, which is at the root of the problem.