I was just watching Dr Steve Phinney on U-tube. Toward the end of his lecture, he was asked about IF

His response - he wasn't a fan mostly because there is no research base

and what research there is, is on people who were starved in concentrations camps, re-fed and died from overfeeding.

He does discuss his rationale

https://www.youtube.com/watch?v=Qk0U006YZ2w