I think there are too many variables to really control for well on this one. Obviously someone who does what your friend did is going to have many factors changing how people interact with them and it will accumulate into and even larger total effect.

I lost 100lbs very rapidly. The difference in attention and little social things was noticeable almost immediately. Same style of dress, moderately kept hair, but otherwise decent personal care on both sides of the weight loss.

What is interesting though to me is that I hit my goal weight right around the time some major life events happened and I pretty much was operating at the lowest self confidence levels I ever had in my life. I was less social and much more withdrawn than before.

I still would notice the “second glances” from folks I never got before, and even friendly greetings etc that were a bit weird at first to me.

I don’t think you can really translate these changes into dating success or whatnot without other life changes though. They just Lower the difficulty level - you still need to put the work in.