Anectdotal reports suggest that individuals who chronically supplement their diet with over 400 mg/day Mg report mild weight gain. Has this been observed in a clinical setting or laboratory? Thanks in advance.
400 mg/ day is the RDI recommendation for Mg by WHO. It is advised to gain that amount or non-significant exceeding amounts of Mg by regular diets. Such people were not eliciting any abnormalities as you have mentioned.
However, if dietary supplements provide additional amount of such Mg rather than the regular dietary intake; outcomes are unknown. There can be toxicity effects.
You may refer the following article.
Article INVESTIGATION OF MAGNESIUM DEFICIENCY AMONG SEVERAL SOCIAL S...