I haven't been able to find any reputable sources about your claim "we can produce it naturally", which sets off my bullshit detector for your entire claim.
You might be more successful if you support what you say with sources.
They are completely wrong. There is some b12 generated by our gut bacteria but it is too low in the digestive track to be effectively absorbed. There is a reason vegans eat foods enriched in b vitamins.
The rest of the sentence provides some important information:
> It is synthesized by some bacteria in the gut flora in humans and other animals, but it has long been thought that humans cannot absorb this as it is made in the colon, downstream from the small intestine, where the absorption of most nutrients occurs.
ok, maybe not everything has been discovered about this, because how come my summer diet of only figs, tomatoes and some leafy greens doesn't cause any b12 deficiency symptoms? (as listed here https://www.nhs.uk/conditions/vitamin-b12-or-folate-deficien...)
but I'm not at all a vegan, it's just that currently there is an abundance of figs around, and why not use those calories. I may consume a fish later in the year, but I'd be curious to understand why some people suffer from b12 deficiency, and some others apparently don't
You might be more successful if you support what you say with sources.