[shlant]

> "It is the primary energy system"

No, it's not [1]. Why do you think many organs[2] including the brain[3] that NEEDS glucose to run?

> "we are in ketosis until we start to eat "food" high in carbs"

No, that's not how that works. Infants are in a MILD ketosis and "this isn’t a function of their diet, but of the developmental period they’re in"[4]

1. https://academic.oup.com/ajcn/article-abstract/59/3/682S/473...

2. https://www.ncbi.nlm.nih.gov/books/NBK22436/

3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3900881/

4. https://www.stopbeingconfusedabouthealth.com/ketogenic-diet-...

[throwaway_kufu]

The brain doesn’t only run on glucose it certainly runs on ketones and ketones are much more efficient at crossing the blood brain barrier. Now when the brain is running off ketones it still needs some glucose, but the body accounts for that by being able to produce its own glucose and doesn’t need it from outside sources like carbs or sugar).

Ketosis is the default energy System, in that all things being equal when a person doesn’t introduce any food they naturally go into ketosis. People literally need to eat certain foods that spike insulin to get “kicked out” of ketosis.

[shlant]

> ketones are much more efficient at crossing the blood brain barrier

Source?

> Ketosis is the default energy System, in that all things being equal when a person doesn’t introduce any food they naturally go into ketosis. People literally need to eat certain foods that spike insulin to get “kicked out” of ketosis.

That is not a sound argument for it being the "default energy system". It makes much more sense that "default energy system" is that which directly provides the energy source REQUIRED by the brain[1]. Additionally, our closest ancestors (primates) were frugavorian omnivores. Ketosis is a state of starvation and the long term complications from it support that[2] but I guess starvation could be argued to be the "default state" of all living things.

1. https://www.ncbi.nlm.nih.gov/books/NBK28048/

2. https://www.thepaleomom.com/adverse-reactions-to-ketogenic-d...

[throwaway_kufu]

> Source?

More interesting, however, is the fact that ketones can provide as much as 70% of the brain's energy needs, more efficiently than glucose. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3219306/

You are ignoring the most important part, humans don’t need outside sources of carbs/sugar (glucose) to power the brain, the body will produce the required glucose internally. So humans can live without carbs/sugar but the same can’t be said without fats.

And no ketosis is not a state of starvation, it’s not clear why you keep saying that, it’s a metabolic state that the body only gets thrown out of when insulin is spiked.

Again it is the default the body only gets knocked out of when introduced to certain foods in certain quantities, which would not have been available pre-ag.

[PudgePacket]

Humans can produce all the glucose they need when in nutritional ketosis or starvation ketosis.

https://en.wikipedia.org/wiki/Gluconeogenesis

[shlant]

but does that make it the "default energy System"?

[shock]

From an evolutionary standpoint it would make sense to evolve the ability to produce all the secondary "fuels" from the most abundant(primary) "fuel". I don't know if things are so in reality, alas.

[randomchars]

[3] is very much not correct. Your brain can just fine on ketones.

Your body is also capable of making it's own glucose, for the organs that need it: https://chem.libretexts.org/Bookshelves/Biological_Chemistry....

[Engineering-MD]

From the review article “Glucose cannot be replaced as an energy source but it can be supplemented, as during strenuous physical activity when blood lactate levels are elevated [14] or during prolonged starvation [15] when blood levels of ketone bodies are elevated and BBB monocarboxylic acid transporter (MCT) levels are upregulated”

And tbh, I would be more inclined to believe the peer reviewed article on glucose metabolism in the brain by an established neuroscientist tbh.

[shlant]

I have edited my comment to reflect that glucose is not the only energy source (although it is still REQUIRED)

[keymone]

Point you’re missing is that glucose that is required can be produced by our body, so there is zero need for glucose or simple carbs (and arguably any carbs) in out diet.

So keto is very much the primary system, breaking down carbs is actually a “holy crap look at all this energy in our bloodstream, let’s secrete insulin and shove it all into lipid cells so that it can later be used BY KETO, OUR PRIMARY ENERGY SYSTEM”.