Regarding the nutrients in general, I would stop everything at least the day before. For instance, if you wanted to see how your body functions without some of the supplements you would have to stop a lot sooner. If you want to see whether your body seems happy with what you are doing, the day before would generally be the time, because it is usually best to fast for at least 12 hours prior to testing anyway.

Some things will probably be decided on a case-by-case basis.

Regarding the B12, I would stop at least three days before the samples are drawn. That will allow you to have some idea how strong your stored B12 is.

rose