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Low Carb/Fasted Endurance Cycling

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  • Low Carb/Fasted Endurance Cycling

    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.

  • #2
    Interesting, you may want to check out Phil Maffetone and his 180 formula to calculate your heartrate to train at to stay in fat burning mode. I have his Big Book of Endurance Training and am almost done. According to his theory, if your low to moderate carb you want to stay in fat burning mode as you have upwards of 40K of calories you can tap into from your fat storage compared to something along the lines of 2-2,200K of calories of glycogen stored in your muscles to access. Go from sugar burner to fat burner, it will take a few weeks. That way you may have something left in the tank to really put the push on at the finish and avoid overtraining. At least that's his theory, we'll see as I plan on trying out his ideas with my mountainbiking.
    You'll never see the light if you're in someone else's shadow, or said another way, life is like a dog sled team, if you're not the lead dog, the scenery never changes


    • #3
      This is exactly the type of information I've been looking foor. I'm one week into my fat adaption process and will be doing endurance cycling. It's good to know that it is possible to do it without GU or quick burning sugar. I'm curious about the Superstartch and whether others have used it with success. Seems like a nice bridge between fat and sugar burning on a longer ride.