Your multivitamin most likely has magnesium oxide in it?
Or magnesium stearate? The Oxide form is not absorbed, and the stearate is not either. The stearate is an excipient added to improve flow of powder into the tablet processing machines.

So you cannot count on either if they appear on a label in that
way.

The average suggestion is 1/2 the RDA in adults to start as a supplement. This is 200mg elemental. Please read my magnesium thread to learn what "elemental" means. Some supplement put it on the label, but most do not.
An example to illustrate is magnesium malate 1000mg.
150mg of it is elemental mag. and rest is the malate. All minerals have this characteristic...of total weight vs weight only of the mineral portion.
I gave the link above in this thread today so you can choose a supplement and how much to take. It is a good time now for you to read the boxed nutrition statements on foods and supplements. Magnesium is not usually listed on foods yet.

The RDA for adult males is about 380mg elemental daily.
Use this nutrition link to see what is in your daily food choices.
http://nutritiondata.self.com/
pay close attention to the serving sizes given in the upper left.

Just paying attention to magnesium often helps many people. It is a basic first base to start at when trying to improve your health.

As far as foods go, you could crush or grind up 3 oz of unsalted almonds and add to real oatmeal (not instant), and get 1/2 the RDA of magnesium. Add some cinnamon or fruit and you have a very nutritious breakfast (or lunch if you prefer it that way).
Real cooked oatmeal, has soluble fiber to help with heart health, and also is easy on blood sugar spikes.
http://nutritiondata.self.com/facts/...cereals/1597/2
has choline, for your nerve membranes and brain,
and good amounts of minerals. Has 10 grams of protein not counting milk or the almonds, which also have some.

Fast processed foods, have the nutrients removed and chemicals
we don't need to take their place.