There is very little significant scientific data to support the idea that magnesium or magnesium supplement tablets can directly lead to weight loss. However, several experts support the idea that a deficiency of magnesium does affect the body in such as way that it may contribute to obesity.  One study has directly linked a deficiency of magnesium, zinc, vitamin C, and vitamin E as risk factors of high body fat percent and central obesity. 
A Magnesium Rich Diet Supports Weight Loss
However, indirectly, magnesium can indeed be a supportive element of weight loss if foods rich in this component are made to be a primary focus of a person’s diet. With rare exceptions, the foods that are rich in magnesium are all perfect for those seeking to avoid fat grams and high-calorie counts.
The list of magnesium-rich foods is virtually synonymous with healthy eating. It includes: tofu; whole grains; leafy vegetables; pumpkin; almonds; and legumes. A few of the other top magnesium foods, such as cashews and sunflower seeds, are higher in, respectively, fat and salt-sodium.
Link between Magnesium Diabetes and Weight
By contrast, much research has been conducted to determine the possible impact of magnesium on Type 1 and Type 2 diabetes. Since many diabetes sufferers are also overweight, this data is currently the closest thing to a clinical look at the link between the mineral and weight loss.
Per the list of magnesium-rich foods above, two separate long-term, large scale studies both concluded that those diabetes patients who ate higher amounts of these items had a less likely chance of developing the human insulin production deficiency. 
There may not be mountains of supporting scientific evidence that magnesium can directly promote weight loss, but there is plenty of evidence that taking too much magnesium can lead to serious side effects that can include, low blood pressure, irregular heartbeat, slowed breathing, confusion, coma, and even death.
It is rare too get too much magnesium from dietary sources. These side effects refer to the overdose of pharmacological magnesium such as that found in supplements, laxatives, and antacids.
 Mildred S. Seeling M.D., and Andrea Rosanoff Ph.D.
The Magnesium Factor
New York: Avery, 2003. Print.
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“Since low magnesium is the key to metabolic syndrome X, with its risk of heart disease, we can see how a diet rich in refined foods can promote magnesium deficiency, and with it, obesity and metabolic syndrome X.”
Mildred S. Seeling M.D., and Andrea Rosanoff Ph.D. The Magnesium Factor