Hi b_jim,
Magnesium has been the first thing I ever found that helps for my POIS symptoms, like 20 years ago, way before I have found this forum.
I think it helps for me because it is a NMDA receptors blocker, so it calms down the anxiety and emotional symptoms, and it also helps regulate potassium level, which seems to help with the hypotension I have when in POIS. Mg is also essential for the production of DAO, an enzyme that eliminates histamine (
http://synergyhw.blogspot.ca/2013/01/magnesium-part-3-wrath-of-histamine.html ). It is often suggested that many auto-immune diseases and metabolic disease are linked to too much histamine, so it could also be part of its a beneficial effect in POIS, at least for me.
I still take a tablet containing organic salts of Mg, equivalent to 100mg of elemental Mg, in my pre-pack ( Equivalent in elemental Mg is variable from one salt of Mg to another, like Mg citrate, Mg chloride, etc..) . Before having more "weapons" against POIS, I would take 200mg , 3 times a day, during 2 days, to survive my POIS acute phase, but this was resulting in loose stools.
Maybe it has a benefit for carbs metabolism, I never thought of it that way. However, I have changed my diet a lot since then, and there are far more few carbs in it, and I usually take them through whole fruits, which make their absorption far more natural, because the fibers lower the sugar spike by slowing down carbs absorption.
Through the year, I also have found that taking a bath with 2 cups of Epsom salts in it is a great way to get magnesium ( Epsom salts are magnesium sulfate salts). It is very calming, indeed, and have no side effects on the guts, because it is then absorbed through skin. A warm bath with candles and Epsom salts, along with some sodium bicarbonate and a few drops of bergamot essential oil was a life saver for me when I had very high level of anxiety !
At one point, I also had a spray bottle with some Epsom salts diluted in water, and would spray my back and legs with it, to get a similar effect to a bath, when I had no time for a bath.