They're pretty different things. Isn't the whole point of religious fasting that it is a different regime, and that the hunger felt is used as a reminder to focus the mind/spirit on higher things than bodily needs. Religious fasts are purposeful privations.
Whilst with IF it's about adopting a habit that stays constant and that negates the potential feelings of hunger by teaching your body that there's no point in complaining food comes in this time-period no matter how hungry it pretends to be. IF is about creating a norm that is no longer experienced as a privation.
If you think about it with a non-religious mind, just abstractly and without prejudice, religions are really good for controlling large populations of people of varied backgrounds and intellect.
How do you get a large populace to eat healthily?
You can either try to convince them with sound arguments and scientific studies. Or you get them to believe in your religion and tell them whatever they need to hear to get them to do it as a side effect. I'm pretty convinced that there's some other motives behind fasting in religions than healthy eating, such as natural scarcity of food during certain times etc. but if you wanted to get them to do it, this would be a great way to do it. And I don't think anyone can deny the potential health benefits of it. After all, what is Ramadan if not IF?
Whilst with IF it's about adopting a habit that stays constant and that negates the potential feelings of hunger by teaching your body that there's no point in complaining food comes in this time-period no matter how hungry it pretends to be. IF is about creating a norm that is no longer experienced as a privation.