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Agreed....the part where it states that "Fructose produced in the brain could possibly lead to inflammation..." made me eye-roll...really hard.

Hwang JJ, Jiang L, Hamza M, Dai F, Belfort-DeAguiar R, Cline G, Rothman DL, Mason G, Sherwin RS. The human brain produces fructose from glucose. JCI Insight. 2017 Feb 23;2(4):e90508. doi: 10.1172/jci.insight.90508. PMID: 28239653; PMCID: PMC5313070.

https://pubmed.ncbi.nlm.nih.gov/28239653/

Glucose can be converted to fructose in the body via the enzyme glucose-6-phosphate isomerase.

https://en.m.wikipedia.org/wiki/Glucose-6-phosphate_isomeras...

if you read Johnson's work, it's typically both. Direct fructose consumption as well as the polyol pathway being on and your body converting 'extra' glucose into fructose.

excess fructose (in particular in ultra-processed forms) causes metabolic derangement but consuming too much of those other 3 esp from ultra processed foods, also activates the "switch" leading to endogenous fructose production and more derangement.

The role of sedentarism in all this is somewhat under-explored though.