Keto Diet and Cycling and Bonking

I have been on a Keto diet for over 2 years now. Still trying to get a better understanding of how it effect endurance cycling. Back when eating a normal diet I learned how eating a couple power bars on a ride would prevent the glycogen bonk.

I am now having a couple F Bombs on a ride which helps with calories and electrolyte drops and also some of the Nuun tablets. What I feel like I am getting a variant of an electolyte bonk over longer distances. Anyone having similar experience or suggestions for foods on long distance riding.

I have been on a keto diet since the summer, and done a reasonable (but certainly not extensive) amount of research on some of this. So, please take everything I say with (at least) a grain of salt. I’m sure there are others who will have some different insights.

One thing I want to get out right up-front, though, is that what you are really striving for is not to be ‘on a keto diet’ but to be ‘fat adapted’. Once you’re fat adapted (which I would guess you are, if you’ve been following a reasonably strict keto diet), your body should convert fat into ketones easily, and then use those for fuel (at least once any sugar you have floating around is used up, since your body will always try to use up any available glucose first).

Now that I have reached a point where my body is fat adapted, I find that I can do rides up to about 100 miles without needing any food during the ride (and have even done a few starting from a fasted state, so I didn’t even have any nutritional fat in my system). I do drink a couple of bottles of ZipFizz along the way (very few calories, but plenty of electrolytes), and always bring a pack of nuts (mixed almonds, walnuts, pecans) along with me, plus a Clif Gel for ‘emergencies’ (thankfully I have not needed it).

This is a good source for training while fat adapted.

That’s a pretty good book, and a quick read. I would recommend adding ‘The Art and Science of Low Carbohydrate Living’ (same authors) as a supplement to this, as the ‘Performance’ book refers to it regularly. (The ‘Performance’ book almost seems like a companion book to the ‘Living’ book.)

1 Like

Anything you notice when running low on electrolytes or has the Zip Fizz had you covered. I am pretty sure I am fat adapted but just seem to get that bonk feel, but I am pretty sure it is from electrolytes.

I had read that exercise while fat adapted allows for a more consistent aerobic endurance effort but as soon as you get to anaerobic effort, the benefits are lost.
Do you find that your rides up to threshold are ok but you bonk with a more strenuous effort?

I’m not sure how extensively this has been tested, but what I have read seems to indicate that you may actually perform better at all levels once fully fat-adapted. (The shortcoming in most studies is that they are short in duration, so the test subjects do not actually get fully fat-adapted.) I don’t really do much in the way of sprints these days, but I will say anecdotally that I have had some of my fastest times up some local climbs since going keto. If nothing else, I definitely have not lost any performance.

Have you lost significant weight since going keto?

When I first started, and was trying to figure it all out with regard to what to eat, and when (as I am doing intermittent fasting, also), as well as get my system ‘balanced out’, I dropped nearly 15 pounds. Now, about 8 months later, I am back to about the same weight I was. Of course, I haven’t been as diligent on the eating as I was at the start (and I’ve been hitting the weights a bit more, also), so I might be able to drop a few pounds. I’m trying to be careful about that, though, because I had a body scan in the middle of this (DexaFit) when I was about midway between the two ends of my weight range, and found that I was at 8% body fat. so, I really can’t lose much more without either starting into the ‘unhealthy’ range, or losing muscle mass (which isn’t something I’m particularly interested in doing).

There is truly a lot to learn and understand about keto (and athletic performance on keto) as it is generally the opposite of what we have all learned growing up: Carbs good! Fat bad! And it’s also not just about the macronutrient composition of the foods, but also the quality (eggs generally good, but eggs from pasture-raised chickens are superior to caged, corn-fed chickens. Same with beef. And butter. And so on.)

Also, and this is perhaps the really tough part: everyone is different. So, what works for me may not work for you. So, there’s a lot of experimenting to be done.

Edit: Most of the weight that I lost initially was likely just water weight, due to burning up some excess carbs, as well as not having enough salt in my diet (which the Standard American Diet - SAD - says to cut back on - because of the high glucose - but which you need to increase on a ketogenic diet - since you’re shedding glucose). I started to get the weight back when I figured the balance.

1 Like

Years ago I did an extensive period of the Atkins diet. Cycling was not difficult but it was different. Took a few minutes to get the fat burning going but once accomplished, seemed like I could ride forever. Lost a lot “Snap” in the muscles…I would not want to sprint. And I am not sprinter anyway, a straight diesel kind of rider…low and slow.

I would think it would be difficult to race on this kind of diet. I finally gave up on the diet as it was too limiting. Lost a bunch of weight though.

I was about 210 lbs and dropped to about 185-190 with just the cutting of the carbs. I bought a Kickr Core in October and that got me off my plateau. Should be able to get to my goal of 175. Just still have that old logic in my head of carbs for cycling. Just need to do some more longer rides to figure out the best new foods.

I was actually thinking about your ‘bonking’ earlier this morning. I wanted to mention that keeping your electrolytes up during non-riding times is important, also. As I mentioned previously, when you cut the carbs from your diet your body won’t retain as much sodium, so you may find that being a little more generous with the salt on a regular basis might help you out on your rides. It’s all a bit of an experiment as to what works for you, of course, but I wanted to throw this out there.

I have dropped over 65lbs on keto. Just going keto doesn’t make you lose weight you still have to reduce calories.I will say that Zwifting on reduced calories does have a big impact on my ability to go more than an hour.I have bumped my calories back up to try and gain more muscle and have been able to stay at the same weight and I can go for longer rides.