When to add carbs



Cycling for few years, on keto for 2 weeks.
Last weekend I did a fasted ride of 75km (46miles) | 29 km/h (18 mi/h).
I’ve ridden 70% in zone 2 (fatburning). I was very content with my ride!
Very cool to not feel bonked, because of lacking carbs. I sipped on 1L water with electrolyte tab during the ride. Really felt the benefit of that one.

My question is, what would be appropriate to eat to attack the climbs like I used to? And avoiding getting out of ketosis. Imo a banana is perfect for cycling. What I had in mind was to eat a banana right before starting, and eating a banana every 30min.

I really really want some insights. My goal is to climb hills without depending on carbs.

(Joey) #2

Since this is your goal - i.e., not to be dependent on carbs for energy - then your question is leading you off in the wrong direction with a faulty premise.

If you haven’t already, please read Voleck & Phinney’s “The Art and Science of Low Carbohydrate Performance.”

If you have read it already, you need to go back and have another look :wink:


Ah excellent! I was hoping for such a reaction.
Cheers :blush:

Could you please elaborate some experiences please?

(Joey) #4

@Tjoe87 First, I should welcome you to the forum. Sounds like you’re off to a good start in checking out this new way of eating. And it definitely affects athletic performance … at first adversely for most folks … but ultimately improves endurance for most healthy athletes once fat-adapted.

I was a runner for decades - eating low fat (high carbs). I’m a bit too old for the joint pounding of street running these days, but through daily non-impact workouts it’s pretty clear that my cardio fitness has only improved. That’s n=1 for you. Now I’ll step aside and let others weigh in.

(Bacon enough and time) #5

Then why eat carbohydrate at all? My understanding is that even Tim Noakes, the author of The Lore of Running and developer of the first glucose gels, has found it possible to run a marathon on a low-carb ketogenic diet without having to carb-load.

In any case, if you want to stay in ketosis, then you will need to eat a low enough amount of carbohydrate to keep your insulin under about 25 μU/mL. How much you can get away with, or how much you will have to restrict your carb intake, will depend on how insulin-resistant you are. The more insulin-sensitive, the more glucose (a/k/a carbohydrate) you can eat without going over the threshold; the more insulin-resistant, the more you will have to restrict carb intake in order to stay below the threshold.

Below the insulin threshold, the body is able to mobilise and metabolise fatty acids. Above the threshold insulin instructs muscles to burn only glucose, not fat, and instructs fat cells to store fat, not let it out to be metabolised. Dr. Stephen Phinney, a researcher into the ketogenic diet and a cyclist, finds that in ketosis he is bonk-proof, but if he eats too much carbohydrate, he bonks.


imo a marathon has a consistent heart rate (trained of course).
Where climbing makes you rise your heart rate to such a level, where you’ll need carbs.
A lot of climbing will wear you out on the ride.(in a classic diet that is!)

I need to do some research (ie “The Art and Science of Low Carbohydrate Performance”).
If i get it right, I should train my climbing on a lower heart rate…

(Bacon enough and time) #7

I’m not sure how this follows. In any case, the glycogen levels of keto-adapted athletes have been shown to be identical to those of carb-adapted athletes, so I’m not sure what the problem is, regardless of whether one considers the elevated heart rate to be endurance performance or explosive performance.

It has also been shown that the cardiac muscle thrives on ketone bodies, in preference to glucose.

However, if you want to eat carbohydrate, go ahead. We are certainly not going to stop you.

(Bob M) #8

I think you could definitely try carbs, though to what extent you might need them is tricky to determine.


Thanks Paul for the elaboration, I really like to be fully fat-adapted.
I’m having some trouble with losing performance because of the transition.
That’s why I thought I’d need carbs on heavy rides.

(Bacon enough and time) #10

How long have you been eating this way? There is a period of adaptation required, as the muscles re-learn to metabolise fatty acids again. In most people, endurance returns to pre-keto levels (or above) within about six to eight weeks.

Explosive power takes longer to return. Just how much longer doesn’t appear to be known. Definitely by two years of keto; though how much sooner than that, no one appears to know. (I don’t, anyway, lol!)


Fruit is the last thing you want, Fructose metabolizes differently, and much slower. You want explosive right now fuel that will run it’s course and then be gone. Dextrose/Cyclic Dextrin/Glucose is what you want. The traditional way of TKD is with Dextrose, typically thrown into your drink, OR you can do it more enjoyable and eat a serving of gummy bears which is pretty much all glucose.

Doesn’t work that way, you use carbs as rocket fuel, you come out of ketosis for a while. Nothing wrong with it, but you can’t do both. You burn off the carbs on your rides and you’re back to normal in the end. What you have to play with is how much is right for you.

(Bob M) #12

I think whether to add carbs or not is complex. Even Zach Bitter adds carbs, but it depends on his training schedule. He also takes carbs on long or high intensity runs. In one of his podcasts, he describes why and he cited to a study for the amount.


This is all very interesting.
Today I did a 90km (56 mi) at 27km/h (16.7 mi/h) endurance ride in Z2 HR.
(Fasted state, salt and 1L of water before I started)

Note that I’m not a highly trained cyclist. I used to ride 50km (30mi) at higher paces.
I’m very statisfied with fat-adapted Z2 riding, it’s much more fun!

Next week I’m riding with friends (30mi) with some climbing. I’m guessing I’ll bonk out quickly.
I’d rather ride alone, so I can decide the pace … With friends there’s always some showing-off …
I’m going to try dextrose just before starting, very curious about this


  • 1 long endurance ride/ week in Z2 without any carbs or food.
  • 1 interval ride with dextrose / week
  • 1 40min interval on rollers (fasted of course)
    Will I still train my fat-adapted capacities in the long endurance ride?

(Jason Rodger) #14

Hi Joe.

Similar to you I started Keto in order to help my cycling, in my case it was to improve endurance as I have always struggled to eat on the bike.

This weekend I did a flat 46 miles in around 3 hrs, zone 2, at an average of around 145w. I felt no need to eat at all, and in fact I didn’t eat for a couple of hours after returning home - no hunger at all. It was very hot in the UK this weekend so I went through about a litre of water an hour. I add some zero carb electrolyte tablets to my bottle, these make a huge difference.

I am two months into Keto, 20-30g net per day, craving carbs often, but managing to resist. Ketosis markers have tailed off on the pee sticks, which leads me to conclude that I am getting fat adapted - no way I could sustain my exercise regime on 20g of carbs a day and feel as energentic as I do at the moment.

Keto has changed my cycling dramatically; I have never been a climber, I have much more of a sprinters build and generally I would be at the head of the pack in most bunch sprints.

But that has gone now, Keto appears to have robbed me of the ability to sprint like I used to. What has replaced it is much, much better endurance and I now have the ability to climb quite well.

So for me, adding back any level of carbs seems unnecessary, fat is very clearly now fuelling my rides, I personally don’t think that small hits of carbs would help me at this point.

(Bacon enough and time) #15

Explosive power does eventually return; it just takes longer than endurance. No one seems to know just how much longer it takes, however. But be patient, and eventually you’ll get your sprinting back, too.