They don't... they sit around all day on this forum... When they hope on their bikes, they diesel along at a Z1 pace. Watch out for the BS anecdotes!
<-note!
The reality for Keto/<100CHO is that your 70% effort will become your new 100%. Do a couple of quick sprints and your done for the day. If you are serious about performance, don't even think about these fad diets. Just eat a proper well balanced diet to fuel you on and off the bike.