[augeias03 (OP)]

Hi

According to Carolyn Dean, because of soil depletion the fruits and vegetables grown decades ago were richer in magnesium than the varieties most of us get today.

Are there reliable studies in this regard?

Magnesium deficience in plants: an urgent problem. 2016. ScienceDirect

[Bored chemist]

In the real world, at the centre of every single molecule of chlorophyll- the stuff that makes plants green- there is a magnesium ion.
It is practically impossible for green plants to be magnesium deficient
Magnesium forms about 2% of the Earth's crust. It's difficult (OK, not impossible) to find soil that has too little magnesium for plants.

Are there reliable studies in this regard?

Yes. As far as I can tell, the studies showed that Carolyn Dean is incompetent (at best).
https://www.casewatch.net/foreign/dean/dean.shtml