You can take some of them on empty stomach but not others. B complex makes me pukey but B12 and B1 on their own do not. I would just take a multi from new chapter, they are okay on empty stomach. I also take Hi Lyte, potassium citrate and magnesium glycinate pills in empty stomach without issues. Do not take magnesium citrate on empty stomach, it will give you the runs.
Generally even on a fast you can still take a very small number of calories worth of food without it disrupting your fasting metabolism. For these medications and vitamins it really doesn’t take much to meet the “with food” instructions. A single saltine cracker for instance is considered enough, and only contains 12 calories, but something like a couple peanuts (5cal per peanut) or almonds can work as well, or a small spoon of peanut butter. Just eat the small amount and immediately follow it with medication then water.
Think about it this way, what our bodies do in fasting is what our ancestors evolved to do in famine or just when food was scarce. From a survival standpoint it wouldn’t be beneficial to turn off this preservation mode prematurely over finding a few nuts, berries, or whatever else they might have foraged. So that tiny amount of food a day isn’t going to stop you.
Some vitamins and medications the requirement is because it can upset your stomach others are because they have to be absorbed through certain digestive processes that won’t kick in without some food. Without food you won’t receive the benefit of those medications.