The question here is why dietary science is so unreliable? There are so many fads. Every year. Many of them with a base in a peer reviewed paper, but all conflicting with each other.

And even reading this comments here: yes keto diet makes me sharp thinking, no actually keto gives 'brain fog', no it is glucose that gives 'brain fog'. It reads like a primary example of some random effects that people interpret to be caused by whatever they currently do.

I am all for going to the source and reading scientific articles - but it is hard. And at some point it is important to admit that we are laypersons in such and such area and the fact that we read (and partially understood) a peer reviewed paper might not mean that much because science is too under the pressure of https://www.gwern.net/Littlewood

Here is another argument for why reading just one peer reviewed article is not too informative in some health related problems: https://astralcodexten.substack.com/p/covidvitamin-d-much-mo...

And by they way the abstract of this particular article is a kind of strange: first they admit that "Neuro-cognitive research has confirmed that glucose, as a main energy substrate for the brain, can momentarily benefit cognitive performances, particularly for memory functioning." - so they admit that the effect of glucose is positive and they even say that it is confirmed. Then they go to their own experiment and report "ingestion of glucose and sucrose led to poorer performances on the assessed tasks as opposed to fructose and the placebo" - so the effect here was negative. But they don't even notice that it is the reverse of what they believe was 'confirmed'. The activities were maybe different - but still.