You could look at this from a learning/adaptation perspective. If you look at keto/fat adaptation, and the way it's sort of looked at in "our" crowd, the paleo/low carber/intermittent fasting types. It can take a while to adapt to a high fat diet, and it's harder on some than others. Why? Maybe because it's been so long since they've eaten a diet that's predominantly high in fat. Various enzymes needed for efficient fat metabolism are kept at a lowish level, in people who have been predominant glucose burners for a long time. Subtle differences in fat intake--35 vs 40 percent, or even 45 vs 35--that's a pretty mild stimulus. 80 percent, now there's a stimulus. The same can be said on the other end, slight increases in carbohydrate can only be expected to give slight adaptations--or maybe none at all, the stimulus could be too weak.

Matt Stone used to suggest full-sugar ice cream and crap like that to develop metabolic flexibility. Just exactly the sort of foods that cause it in the first place. I sometimes think of mixed sugar/fat foods as "white noise" foods. Rat pups exposed to real white noise fail to properly develop the part of the brain that discriminates between different sounds. So they hear any noise--the whole region lights up, they get seizures. The cure is exposing the animals to various simple tones, get the brain to slowly rewire itself. Complex chords wouldn't work, only simple tones. If I wanted to take a shot at metabolic flexibility, I wouldn't expose myself to a complex food with a middle of the road macronutrient content, I'd spend some time in the extremes. Learn scales before chords.

Acute opposed to chronic stress can improve blood glucose in rodents. Hanging rats by their tails, and other mean stuff. Probably have to fit any exercise protocols where an electric zap grid is the motivator as well. I guess it depends on how often the whippings were.