Depending on what you’re referring to when you say “athlete”, you really shouldn’t be fasting. Fasting is highly associated with getting into autophagy, and this is not a state you should be getting in if you’re repeatedly doing high intensity cardio, lifting weights, etc.
This is because you should be eating protein (especially if you’re lifting weights), and protein is always going to inhibit mTOR, stopping autophagy. Fasting & athleticism do not go hand in hand (unless you’re referring to fasting that’s under 24hrs, then ultimately it’s inconsequential & the benefits from said fast are insignificant anyway)