That's a good point and I didn't have time to read the full research paper. I still don't see a reason why <1g supplemental magnesium daily would cause any harm in generally healthy people. The body will excrete excess magnesium that's not absorbed, and I haven't seen any evidence that this puts an undue strain on the kidneys at this low of a level. The majority of people would likely absorb the Mg anyway, since Americans are so deficient.

I totally agree with you that diet should always be the first option (although remember that the nutrient levels of produce have dropped drastically due to modern agricultural practices which is part of the issue), and it's best to get an intracellular magnesium test if you're supplementing with high doses, to make sure that you're not wasting your money and potentially throwing other electrolytes out of balance. The problem is that most people can't afford this test and it isn't usually covered by insurance.

Personally I was already eating a nutrient-dense diet and had to pay almost $500 out of pocket for this test, and I was still deficient in magnesium, which is why I started supplementing. But I recognize that not everyone has that option. For those who can't afford such a test I tend to think that supplemental magnesium is much more likely to help than harm them.