I just wanted to share a recent experience with those of you who are interested in fat-adaptation and the intersection of low-carb and performance cycling. I am 9 weeks primal. For whatever reason it was easy for me and for the most part I don't cheat. I am not carb-resistant, and I don't have a problem with primal carbs per se, but I really like the idea of fueling as much as possible with my own body fat.

So on Saturday, I had a 200k ride scheduled with some friends. I haven't really been riding, apart from to and from work, but I have a long history of cycling and racing and my legs are never far away from riding condition. After reading Peter Attia's blog about long, hard cycle training on a ketogenic diet, reading about Stu Mittleman, and then the success story on Mark's blog where the fellow had ridden 170 miles close to fasted, I decided that I would try and ride the 200k carb-free.

Oh, and I wore a heart-rate monitor so that I could objectively evaluate my effort level.

I started my morning with Bullet-proof coffee. Not something that I could do every day, but it seemed perfect for the task ahead. The two foods I brought with the intention of eating were two bags of almonds and a squeeze bottle filled with a mix of coconut and olive oil. I also brought along a good supply of carbs as backup fuel so that if I did bonk, I wasn't relying on gas station food. These carbs included dried apricots and apples, and two pouches of ucan superstarch. Because it was warm out I also brought a roll of Nuun electrolyte tabs that I added to every bottle of water. Oh, and a small (230 cal) bag of roasted peanuts for when I wanted something really salty.

The first time I felt hunger was about 30 miles in. We had been working much harder than I had planned, and my heartrate seemed to hover around 140 or so, which is over 70% of max for me. I was getting quite worried that I had bitten off more than I could chew. At the first water stop I had about 1/3 of one bag of almonds and immediatly felt better.

Then came the climbing. Not steep but sustained and my HR was over 160 for a good while. Rolling hills after that with HR between 120 and 150. It did get up above 170 later on during a VERY steep hill.

Amazingly, hunger was never an issue. I finished my bag of almonds and the peanuts, did not touch my second bag of almonds or the dried fruit. I probably had three shots of the oil mixture (about all I could take to be honest!) I did consume a packet of the super-starch. This was actually a mistake. We were 8 hours in, had 20 miles to ride and I knew that we would not stop for water. Never having done anything like this, I was listening intently to my body for any sign of distress. I could just feel the whisper of the beginning of a bonk, and wanted to make sure I kept it at bay, so when we filled our water I put the super-starch in one of my bottles (bonking is not fun). By the time I had finished my bottle of plain water I felt better, but needed more water, and the starch water was the only option. It was lemon flavor, and it tasted awful. I don't really consider it as breaking my fast because a) it was during the last hour of the ride after 8 hours and b) it was only 25g of carbs.

Amazingly, I still had energy later in the day to ride to the store and walk the dog!

Thanks for reading what turned into a long post, but I wanted to share with those endurance athletes who are nervous to go low carb that it IS possible, even sustaining climbing HRs of 85-90% on a 9+ hour ride.

For numbers geeks my average HR was 129, almost exactly 70% of max, and my monitor claimed I burned 6000 calories, which seems pretty optimistic. The ride was 40% dirt roads so the slow average speed of ~12 MPH makes sense.