Fat adapted athletes

Any advice for going fat adapted? I am a sugar burner but am switching because I was diagnosed with epilepsy this year and the meds make me feel bad so going keto is my only other option.

Its only been a few weeks but am wondering if I am truly fat adapted and have a gel or 2 during a long intense ride will I remain in ketosis?


I’d say that this is a discussion you need to have with your physician or your dietician. Nobody on a internet-forum should give you advice on potential life changing dietary intake.

As far as fat adaptation this takes a while and as far as I know you don’t disturb this with minor “injections” of approx. <50kcal.

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Thanks, I have already had this conversation with my doctors and they feel the ketogenic diet is best to control my symptoms.

I am trying to navigate nutrition and still be able to nail my key workouts.


I don’t check for ketosis. I just stay more or less below 50 grms carbs a day and no refined sugars at all. I have tried eating carbs on rides to fuel the intensive stuff as I read it was wanting in HFLC athletes. Can’t say I noticed any significant difference in my case. Either in performance or induced carb cravings. It did cause digestive disturbances though during the race so I have stopped. I guess in your case the medical advice is primary. Did they advise strict keto or just HFLC. If the latter then I would not sweat the on carb intake on the bike.

I’ve been on a journey loosing 37kg with the help of intermittent fasting and I went on the road extreme as I usually do. Meaning I was fasting Monday and Thursday and also only eating between 12:00 - 20:00. So basically I did my Tuesday HIIT-sessions without having eaten since Sunday at 20:00. And Thursday sessions without eating since Wednesday 20:00. I didn’t have any problems executing these sessions. But we’re all different and we respond differently. In my case the whole fasting part wasn’t very difficult. However not eating carbs at all would most likely not lead to anything positive. Sorry but endurance sports and keto-diets aren’t friends.

More reading in this topic:

That’s fighting talk

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Insofar as you’re doing this for seizure control, keto can work really well. I probably wouldn’t recommend adding carbs to workouts given your situation, but there probably is a place for targeted carbs otherwise. All the research on seizures control I’ve seen suggest the effectiveness is directly correlated to the level of ketosis reached… so being at a low level of “ketosis” may not be as effective as a deeper level – and any carbs you consume will make keeping that level up. But if you can tolerate a few gels while keeping your symptoms at bay, then that’s your call – it’s very individual.

From a sports angle, it’s going to take a while to get your mojo back. Make sure you’re getting enough sodium – it helps. I wouldn’t recommend using carbs to bridge, it just takes time. Not sure what your performance goals are, but I’ve managed to get to 4w/kg on keto and rarely use carbs with workouts.

I’m generally curious what fat sources you plan to emphasize? I’m firmly in the seed-oil (vegetable) bad camp, but I know the medical profession has a tendency to favor them over saturated or mono-saturated sources.

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My understanding is (1) yes, consuming a sugary gel will take you out of ketosis and (2) fat adaptation will noticeably limit your high intensity efforts.

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Is this your understanding or do you know this for a fact?

Are you fat adapted yourself?

I’m not currently keto but do intermittent fasting. I alternate between 18:6 and OMAD. I train fasted in the mornings and ride up to 2 hours without any hunger.

Once you get used to it, it’s fine. I assume it’s even easier once you’re keto. You can get keto gels and snacks which might not be necessary but could be helpful psychologically.

Good luck.

It takes me all of 8 weeks of being in ketosis before I feel at a normal level on the bike. Prior to that I struggle completing workouts. I generally just feel like death at certain times on the bike, or just hit walls out of nowhere. Once I’m adapted though, that all goes away and the only thing I fight with is balancing my electrolytes.

Note for my 8 weeks comment. It can take 8-12 weeks, even longer for certain people until they are fat adapted. If you stay in ketosis the whole time you’ll know when the switch is flipped. Even then, you can still see fat adaptation improvements over another year or two.


I think this is an important point to emphasize. It takes time. The whole keto flu thing is not the end of the adaptation phase. All the studies I have read that cast doubt on keto for endurance athletes were all short term. The studies did not really include long term samples. I imagine such longitudinal studies would not be cheap. I gradually transitioned over the course of a year. I went there before my TR journey so it is difficult to state categorically my high end impact. Do I struggle with VO2max sessions? Well yes but that’s the point of them. Do I feel like I am bailing out too much? No more than anybody else on here. On the plus side of the ledger is me hitting PBs this year on VO2max climbs I have ridden for over a decade (from before I went HFLC). So there is a big hole in the study data. You are an N of 1. Transition takes time. From what I have read even in ketosis the glycogen burn is sufficient enough to burn in ride fueling without much risk of dropping out of ketosis. If strict is needed why bother with it at all? There is no need to risk your general health for cycling. Hold fast and allow your body the time it needs to complete the adaption process. My random internet person tupppence

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FWIW. In ride fueling for me: smoked almonds and electrolyte tabs in the bottles. Only for 4 hour plus rides and not really sure I need the nuts. Just use it as a sort of reward.

Have a look at this website. Lots of useful information.

Personally, I don’t think this about being strictly “fat-adapted” or otherwise. What, I think, we should be striving for is metabolic flexibility, relying on fat and carbs where appropriate.

I’m fat adapted and can produce up to ~90% of VO2Max Power using fat (recent lab as exchange test). However, I also use CHO as appropriate (e.g., racing, Hill Climb events).

The vast majority of my training is fasted, but if I’m doing VO2Max and above, I use CHO - not because I “need to”, but because the quality of the session is better (as is perceived recovery).


I like that characterization. In this case it is something different. It is a medically recommended approach. So it is externally inhibited. CHO may not be recommended here. I don’t know. From the incidental reading about this it is implied that strict keto was required for epilepsy mitigation. I am not a medic. Gluconeogenesis may be an alternative approach but I haven’t read much about this This is really for @Matt_Thompson medical team to answer for him.