Hey there forum,
since this is my first post, I’d like to give a quick overview of my journey and my experience.
Although I have not had any medicial reasons to lose weight, I had (and have) some pounds to give away and started to look at what tips and tweaks where around 3 years ago. Starting with a paid low carb course by a german celebrity, I heard more and more details about why low carb is good and sugar / starch is bad for me. Since I started running (again) after having gained weight while my wife was pregnant with my first kid in 2011, I have always had the information about how import carbohydrates are especially when it comes to exercised. So this inconsistency always made me wonder which side of the medal is the shiny one. Eating starch / sugar made me have stomachache and I unconsciously lived a low card live.
I ran a marathon in fall 2016 being a carbohydrate runner, trying to eat as much gel packs as possible and trying to survive the aching belly during running. It was ok with a time of about 4:40 (for a guy with 1.70m and 95kg) but not with a body feeling that was close to be comfortable. My trainer did a spiroergometry to measure how much fat I am using and it was not that good. So my next marathon in spring 2017 was with a 4:30 a bit better, but still dominated by belly aching and carbohydrate gel intake. In 2017 I started triathlon training and did a middle distance (1.9 km swim, 90km bie, 21km run) on cyrbohydrates, too. In the last transition prior to running I had lost my gel packs and really suffered in the final discipline without the carbohydrate packs I was used to.
During the last off season, I heard some of the dudes podcasts, read some blog posts about ketogenic athletes and some topics in the forum here. And I skipped my goal to run sub 4:00 on the marathon, fired with carbohydrates in favor to going fat adapted. In addition to my already low carb diet, I started adding fats more and more by reducing protein shakes and un natural stuff. I added fasting periods of about a week, trying to do some low intensity workouts in fall 2017. Puh, they where hard and I have not really been able to do fast runs at that time, but I kept going on. Together with the podcast, I continued trying to be in ketosis and die more and more slow and fasted long runs, which lead to that moment where I made the decission to try running on keto. It was a 25km run that I did fasted with the dudes binge hearing on my headset. It went really well and I felt that going keto on running is no problem for me anymore - more than that: I felt the clarity everybody was talking about.
So project keto-marathon started for me and I did it last week in Hamburg. I felt really great but have to change some things to really be a keto adapted athlete.
- I had cramps and my sweat really tasted salty, I think I have to take some salt during longer runs / bike rides.
- I was used to drink one or two glasses of wine the evening before races just to come down. This kicked my out of ketosis and I think I felt that after km 28.
- I did not enough long runs - which lead to aching in my locomotor system but that has nothing to do with keto.
To sum it up: I felt great, was happy during the run and had not a single belly aching moment. Yes, I was very slow but that is something I put up with. I will definitely continue racing and training on keto on my next races (olympic triathlon in 2 weeks and a middle distance triathlon end of june). If anybody is interested in talking about becoming / maintaining a ketogenic athlete I would really be happy about a response.
And: I really would like to thank @carl and @richard for their inspiring podcast. What a great ressource that is. Maybe there are some people from Germany that like to do a ketofest 
Mirko