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
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.
^^^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, normal in FASTER, and similar performance in both.
correction: ketoadapted athletes were LC for ~20 months, not 9 years!