Malic Acid and Magnesium was reported effective in this 1995 study, Treatment of fibromyalgia syndrome with Super Malic: a randomized, double blind, placebo controlled, crossover pilot study.Russell IJ, Michalek JE, Flechas JD, Abraham GE., May;22(5):953-8. J Rheumatol. 1995. The study recommended further study which has not happen over the last 17 years.
Various internet sites cite studies that are not on PudMed, for example
- 1992 study received an oral dose of 1200-2400 mg of malate (malic acid) and 300-600 mg of magnesium over a four and 8 week period [ Abraham GE, Glechas ID. “Management of fibromyalgia: A rationale for the use of magnesium and malic acid.” Journal of Nutritional Medicine,1992;3:49-59.]
- “Nevertheless, Mg supplementation was followed by an improvement in Mg body stores, in serum vitamin E and its interrelated stage of lipid peroxidation.” 
- “70% have improvement 
Many studies have found that magnesium is low in Fibromyalgia and Chronic Fatigue Syndrome patients. Low levels are associated with low levels of glutamine. Taking magnesium supplements have reduced symptoms according to studies.
In terms of microfloras, magnesium is required by Bacteroides which are very low in 25% of patients. Bifidobacterium (also low in patients) plays an important role in extracting it from food. A cascade.
At this point I must point out that studies found only 50% of CFS patients are deficient in magnesium. The improvement reported was on the average of the study group. Not every person will have an improvement. Given the low cost and no apparent down side risk, it should be tried — especially when symptoms flare. Dosages may depends on the degree of deficiency seen.
Magnesium and Malic Acid are both pure chemicals and thus any supplement grade source is adequate.
- Magnesium Malate:
I tend to favor Magnesium Malate because it is a needed for the Krebs Cycle.