Long-term fat adaptation

Recent comments about FASTER have upgraded this study to “the only long-term study on fat-adaptation.”  Needless to say, I disagree.  Again.

Side note: FASTER had no randomization or intervention (ie, confounded by selection bias, among others); they basically recruited long-term low carb & high carb ultra-endurance runners and measured the stuffings out of ’em.

Ultimately, they showed a very high maximal fat oxidation rate in low carb ultra-runners, 1.5 grams per minute.  This is important because MAXIMAL HUMAN FAT BURNING CAPACITY




In previous studies on SAD (Standard Athletic Diet haha), maximal fat oxidation at similar VO2max% has been reported to be much lower, <1 g/min (eg, Hetlid et al., 2015 and Volek et al., 2016).



fat oxidation rate


Part 2. In the context of #ketoadaptation (or fat adaptation or whatever you want to call it), “short-term” is zero-to-three weeks whereas “long-term” is >three weeks.  Because objectively, beyond that point, no further relevant physiological & metabolic adaptations occur.

Actual physical performance can and will improve thereafter, although this is an effect of progressive training, not moar ketoadapt.



The original evidence for this came from keto-exercise studies lasting 1, 3, 4, and 6 weeks.  Tl;dr: performance tanks week 1, is restored by week 3, and stays there weeks 4 to 6.  So basically, the physiological adaptations happen within 3 weeks and we don’t expect a ketoadapt-induced spike in performance, reflecting no further adaptations, after week 4.  Again, performance may increase thereafter, but this is due to progressive training.

Yet some will still argue the epic fat oxidation rates in FASTER suggest: 2 years LC = more adaptation.

…however, this isn’t our first rodeo


Part 3.  Phinney and colleagues did similar studies in the early 80’s.


Phinney fat oxidation

^^^if my calculations are correct, three-week ketoadapted athletes were burning ~1.6 grams of fat per minute at 64% VO2max.  Compare that to FASTER’s 1.5 grams per minute at 70% VO2max after ~2 years.  Slightly higher fat oxidation at slightly lower VO2max%, as expected (maybe), but basically the same.  This suggests the adaptations in mitochondrial quality and quantity (and/or whatever else happens in ketoadaptation) are in place within about a month, and don’t change much thereafter.

Also, it may be a bit of a stretch, but since performance of the long-term ketoadapted athletes wasn’t superior to the SAD athletes, we may even infer that gains in performance are unaffected by ketoadaptation.  Maybe.

2 years of keto diet, same degree of “fat adaptation” as 3 weeks. QED.

This is confirmed by studies on physical performance and maximum fat oxidation rates.

As to physical performance, most evidence suggests high intensity work and even explosive power can be achieved on a ketoadapted metabolism.  This has been shown with studies on wingate, standing vertical jump and long jump, legs closed barrier maximum test (whatever that is), and bench press, among others.


Those studies might not reflect Olympic Tests of Greatness or correlate with Gold Medals, but: 1) they’re mostly neutral or positive; and 2) there aren’t many negatives.  Ie, weight of the evidence favors “positive.”

A list of some very accomplished n=1 ketoadapted athletes can be found here.

Lastly, I don’t think maximal fat oxidation rates reflect physical performance per se, but it’s cool to know because science nerdism.

And fwiw [non-sequiter], glycogen is probably not a key mediator, because it was lower in Phinney’s study (cyclists), normal in FASTER (runner), and similar performance in both.

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  • Tuck

    Where did you get the 9 years figure?

    It’s a good point to make that no one becomes a good athlete without a lot of training, keto-adapted or not.

    It’s also a good point to make that there’s more than one way to improve performance. Stopping less for food in an endurance event or having less digestive distress or hypoglycemia (bonking) will improve performance, if not pace while moving.

  • Eric – Golden, CO

    In FASTER they also measured mitochondrial density in the muscle tissue biopsies but they haven’t released that info yet.

  • Wab Mester

    Nobody seems to mention that RQ doesn’t change much at rest. Is there any evidence that the sedentary on LCHF can become “fat-burning machines?” Isn’t the signal for mitochondrial biogenesis “oxidative stress?” Would that be signaled in the sedentary on a LCHF diet?

    BTW, I’d love to see somebody outline all the adaptations that take place on a LCHF diet.

    • outlining “all the adaptations” would be quite a task…
      here’s a start http://bit.ly/1oYn9vM, and other changes may be directly related to those

    • the signal for mitochondrial biogenesis in this #context seems to be PPAR & PCG1a, mediated by high FFA flux

  • Colin Champ

    Great article Bill.
    Closed Barrier Maximum Test should be when they close you in some kind of barrier and see how long it takes for you to go crazy and get out. Would make studies more interesting for us all!

  • Aaron Somes

    I would like to shake the hand of the individual that included Trogdor in this article. That is all.

  • George Thomas

    I always thought it was a load of crap whenever I heard certain keto gurus spout nonsense like “you need to be strict keto for at six months before *full* fat-adaptation occurs”. Bro-science on steroids.

  • Low Muscle Glycogen and High FFAs Modify but Do Not Prevent Exercise-Induced PDH Activation in Human Skeletal Muscle https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2797931/