It is well known that cows technically don't "eat" the grass, they actually "eat" the microorganisms living in their stomachs, hence why their feces are mostly grass. If cows "ate" the grass, the grass would be "gone". Because humans are obligate carnivores, when we eat steaks, we don't poop out a bunch of little steaks: what comes out is unrecognizable and very different from herbivores.
In the Framingham Offspring study, it was found that there was no difference in vitamin B12 levels between people who ate meat and people who didn't. The reason why that study showed no difference, it seems to me, would be because the demographics were most likely all eating a plant based diet, even while eating meat.
A typical "balanced meal", even for so called "meat eaters" (meat, veggies and bread etc) is still a plant based diet. The various demographics in the Framingham Offspring study were most likely all in glycolysis (as opposed to ketosis). In order to trigger ketosis, one must eat around 80% to 90% fatty protein for multiple days straight. Glycolysis, on the other hand, can trigger in a matter of hours. Given the ratios of modern diets of today, even the meat eaters participating in the study probably ate less than 50% meat, which would trigger chronic glycolysis.
In a paper about the Framingham Offspring study, it states:
"Oddly, the researchers found no association between plasma B12 levels and meat, poultry and fish intake, even though these foods supply the bulk of B12 in the diet. "It is not because people aren't eating enough meat," Tucker said. "The vitamin isn't getting absorbed."
How does that Offspring study handle chronic glycolysis in the design? Wouldn't chronic glycolysis interfere with the proper absorption of B12, and, wouldn't that be a plausible realm of exploration given the "odd" nature of the results?
Sugars from glycolysis directly affect available B12 in the blood which could shed light on the odd nature of the results from the Framingham study, in the participants who ate meat while still being B12 deficient. Sugar depletes B12. "Meat eaters" with B12 deficiencies are most likely in chronic glycolysis (that's a big part of the reason why they're deficient).
It is well known in the medical literature that chronic glycolysis leads to aging and neurodegenerative disorders because these types of brain disorders and accelerated aging, in general, all have a lot to do with B12 deficiency.