As a feminist, I was VERY irritated when I heard about this " beach" diet, because it seems to be perpetuating the idea of women feeling pressured to look slim.
That irritation may have caused others to dismiss intermittent fasting as a "fad", which is a shame, so I'd like to add a scientist's perspective here (although from a v different scientific field):
Hormesis, on which both intermittent fasting and HIIT (High Intensity Interval Training) are based, may have benefits for health, aging and fitness. The benefits of HIIT are well-proven; IF research is ongoing.
So, hormesis is an exciting areas of science which is growing rapidly.
5:2 itself does not have scientific trials, but it is reasonable to extrapolate from extensive work on other IF regimes.
Michelle Harvie's research and human trials on her "2-day" diet (very similar to 5:2) were to reduce the risk of breast cancer for high-risk women.
Her success re weight loss and risk factors with either Mediterranean or low carb diets on 2 Fast Days are accepted and referenced within the scientific community
Varady's ADF diet, with fasting every other day, involved umpteen human trials and hundreds of test subjects thoroughly examined.
Her peer-reviewed results and papers are also regarded as respectable and conventional science.
A major advantage of 5:2 is that it can fit all kinds of nutrition regimes - low fat / low carb / veggie / vegan / Paleo .... - so would be an option for most overweight people.
Since obesity is such a major problem for the NHS and so many in the UK are doing 5:2, I wish an official body would conduct proper scientific trials on this version of IF