According to Chris Masterjohn, B12 is interesting and unique because we can only absorb enough for a day from a single meal. To absorb more, you have to space the meals out about 5 hours in between. You can eat a day’s worth of B12 at each meal and store 2 days extra for the future. We store the excess amounts of B12 in our liver for future use, but only up to a maximum of 14 years or so (I forget the number).
What interests me the most is this may explain why many vegetarians and vegans believe that they do not require B12. This may have even confused former NASA scientist and vegan Ray Cronise who tested his B12 status after a remarkable 21 day fast and then believed that B12 was being created in his body. I think the reality is it was not created, but simply stored and released.
I believe this was this interview where Ray mentioned his 21 day fast and the B12 testing, but this was a few years ago when I listened to the interview; I actually heard it in audio format as a podcast so it very well could be a different second interview not available on YouTube.
So in short, it would be best to take a B12 supplement at each meal unless 100% sure enough B12 is present in dietary sources at each meal.
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