Peter Attia has taken the quantified self concept to a new level. He is a long distance swimmer and cyclist who put himself on a ketosis diet and monitored it like nobody else has. His and explains how the new generation of low carbohydrate endurance athletes are performing so well. This is a long video (1h, 17m), but I strongly suggest checking it out if you are considering a very low carbohydrate diet for performance reasons. Video link starts 57m in with a nice summary point, but I encourage you to watch the entire video.