That sounds like a typical fad diet. What differentiates it, and what evidence do they have for their claims?
Personal note: I've been following this diet since Jan 1. I also run ~ 70 miles/week. I've run 3 of my best marathons this year and lost 5 stubborn lbs (145 -> 140, I'm 5'8"). There are other styles of intermittent fasting. I'm enjoying this way of eating.
Aside, a related BBC/Horizon documentary I saw years ago flipped the question of obesity on its head and asked: Why Are Thin People Not Fat?
Looking at 5:2 simply as a "pattern of eating", however, makes it easier to consider not only the apparent health changes but also other potential benefits, including:
- Reduction of IGF-1 - Prolonged period of not eating as a means to promote cell repair - Shining a light on the cultural norms around eating three square meals a day with/without snacks in between.
After watching the documentary it seems like 5:2 may be more than just another "fad" diet.
And the subsequent discussion on HN: https://news.ycombinator.com/item?id=10863626