Beyond how ridiculously reductive this becomes, it's impractical. You have to have carbs for your brain to run.
The brain can run well on ketone bodies (which the liver makes from fatty acids). In fact, causing the brain to run on ketone bodies is used by doctors to treat illness (and not just epilepsy).
If you have any sense for your health you will not have regular intake of sugar, white bread, potatoes crisps, rice cakes, any thing with a high GI.
Some carbohydrates reduce your risk of diabetes, and if you're smart you follow the evidence and you eat these-
So any argument based on “it worked for our ancestors” is flawed.
“It worked for our ancestors” could be the beginning of an idea for research, but certainly does not take you much further than that.
"You have to have carbs for your brain to run" doesn’t make sense. You have to have sugar in your brain to run, but that sugar surely can comes from fat as well.
> Beyond how ridiculously reductive this becomes, it's impractical. You have to have carbs for your brain to run.
No. People live on no-carb diets just fine and enter ketosis. (And in any case, the comment you replied to only talked about sugar, not carbs in general.)
'A low-carbohydrate diet based on animal sources was associated with higher all-cause mortality in both men and women, whereas a vegetable-based low-carbohydrate diet was associated with lower all-cause and cardiovascular disease mortality rates.'
https://pmc.ncbi.nlm.nih.gov/articles/PMC2989112/
It is of course rather difficult if not impossible, to have a vegetable diet completely devoid of carbohydrates.
Alas, it doesn't have much bearing on the part of the comment I wanted to focus on 'You have to have carbs for your brain to run.' Because the diets in question here still have some carbs. (And the changes in mortality rates are fairly modest, too.)
What I wanted to say is that even if you eat no carbs at all, you brain will still get its energy. You won't just keel over after a while, like if you didn't eat anything at all henceforth.
Of course, there might be second order health effects, like the study you linked suggest.
There are other metabolic pathways to produce glucose (or produce ketones). The other pathways ‘push’ the body more since they have to do some conversion. This ‘extra effort’ is considered to be more healthy.