New review out of Pittsburgh, gets some things right (Sherrier and Li, 2019).
... takes some things out of context, too, like saying "beneficial effects of ketogenic diets on cancer," as if that's an established fact.
It's not... but still, let's focus on the positive
Some ground rules:
- ketogenic diet =/= fasting
- nutritional ketosis =/= exercise
- carbs =/= obesity
- the opposite of intermittent fasting isn't diabetes
Another ground rule, or maybe a disclaimer: I've read and blogged about nearly every study on ketoadaptation & physical performance that's out there. My 30000-foot view is: "it's fine."
Given adequate time to adapt (~3 weeks), keto doesn't wreck physical performance. Some studies show a little positive, some a little negative; net sum = neutral.
Other energy systems kick in and performance is maintained. Any further gains from training are just that: gains from training (not gainz from moar ketoadaptation).
Keto isn't muscle-sparing or anything like that, and you likely need more protein (not less) to maintain muscle, but this also isn't really that big of a deal.
This article is pretty good, imo. Covers a lot of topics ranging from glycogen on keto to fat balance to exercise efficiency and more.
Please don't lecture me about how many grams of ATP per carbon or Oxygen or whatever in this #context and then conclude, "therefore ketoadaptation should improve exercise performance" because we have ample empirical evidence that it doesn't. Turns out, none of those theories worked. Exercise on keto is just as good as exercise on non-keto. It's not better.
Next up to bat: glycogen.
My Tl;dr: there's no intrinsic physiological relationship between nutritional ketosis and glycogen storage. Some studies show reduced glycogen on keto; others show similar levels. Phinney showed lower glycogen after about a month of ketoadaptation; Webster and colleagues showed something similar after ~8 months. However, FASTER showed no effect of nutritional ketosis on glycogen levels after ~20 months.
Therefore, the ability to maintain equal levels of glycogen on keto doesn't not appear to be an effect of duration of ketoadaptation. Maximal fat oxidation rates peak at around 3-4 weeks and don't increase much thereafter. I don't think something occurs after the 8-month mark which magically triggers increased glycogen storage capacity lol
apples to oranges
Those are 3 separate studies; different athletes, different sports, different diets, etc., etc. I do like the observation that similar levels of maximal fat oxidation (1.5 grams/minute) were reported by Phinney and FASTER, which is one of the reasons why I cite 3-4 weeks as the amount of time required for adequate ketoadaptation (and you don't get more ketoadapted after then).
Does exercise help with ketoadaptation?
Yeah? Maybe? Relevance?
Exercise is like, an hour a day. Ketoadaptation takes 3-4 weeks. Why are you on a ketogenic diet? for a quick experiment? Context.
Weeks - months - a lifetime (for some). I don't think keto doesn't work for some people because it didn't jive in the first 3 days (thus, exercise to enhance ketoadaptation wouldn't have been the make-it-or-break-it moment).
Rather, I suspect some carb creep happens; they stop eating avocados, maybe weight maintenance maybe not, but whatever happens and they're back to baseline diet (for most). Not "OMG I CAN'T HANDLE THE PRE-KETOADAPTATION PHASE."
So yeah, everyone should exercise and yeah, this might help ketoadaptation.
The authors kept saying "so, ketoadaptation should enhance exercise performance"
BUT IT DOESN'T.
Followed up with the straw man reasoning that studies on non-ketoadapted exercise show blunted performance. UGH. Studies on 20-month ketoadapted athletes show no difference in physical performance compared to high carb athletes. What more evidence do you need to see?
The last section: possible biomarkers of ketoadaptation?
I know, people want the equivalent of a glucometer for everything. My answer to this question is more applicable in the laboratory space, but I think it's the closest thing we have to muscle biopsies for mitochondrial quantity/quality studies. And that's maximal fat oxidation rates. Once you hit around 1.5 g/min, that should indicate a time point when physical activity is back to baseline.
What do you think? (on any of the abovementioned topics)
That's all for now!
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