Can magnesium bisglycinate cause diarrhea?

Can Magnesium Bisglycinate Cause Diarrhea?

Yes, magnesium bisglycinate can cause diarrhea, though it is significantly less likely to do so compared to other magnesium formulations like magnesium oxide or citrate. 1, 2

Mechanism of Magnesium-Induced Diarrhea

All magnesium supplements can cause loose stools through an osmotic mechanism—poorly absorbed magnesium ions draw water into the intestinal lumen, increasing fluidity of intestinal contents and producing a laxative effect. 3 For each millimole increase in fecal magnesium output, fecal weight increases by approximately 7.3 grams. 4

The key diagnostic threshold is a fecal magnesium concentration greater than 45 mmol/L, which strongly suggests magnesium-induced diarrhea. 5, 4 Normal subjects with formed stools have fecal magnesium concentrations below 45.2 mmol/L and fecal magnesium output below 14.6 mmol per day. 4

Why Magnesium Bisglycinate Is Better Tolerated

Organic magnesium salts like magnesium bisglycinate (glycinate) have superior bioavailability compared to inorganic forms like magnesium oxide or hydroxide, meaning more magnesium is absorbed systemically rather than remaining in the intestinal lumen to exert osmotic effects. 1, 6 This better absorption translates to fewer gastrointestinal side effects, including less diarrhea. 1

In contrast, magnesium citrate creates a stronger osmotic gradient and is particularly effective for constipation precisely because it causes more pronounced gastrointestinal effects including diarrhea and bloating. 1 Magnesium oxide is poorly absorbed and commonly used as a laxative at doses of 1.5 g/day for chronic constipation. 1, 6

Clinical Context and Dose-Response

The likelihood of diarrhea depends on:

• Dose: Higher doses increase the osmotic load. Magnesium oxide at 1,000-1,500 mg daily is used therapeutically for constipation 6, while supplementation doses of 320-420 mg daily (the RDA) are less likely to cause problems. 6

• Individual tolerance: Some patients cannot tolerate any oral magnesium without developing loose stools. 2 For these patients, magnesium chloride capsules or parenteral administration are the best options. 2

• Formulation: Liquid or dissolvable magnesium products are generally better tolerated than pills. 1, 6

Practical Management Strategy

If you develop diarrhea on magnesium bisglycinate:

1. Reduce the dose or split it throughout the day rather than taking it all at once. 1

2. Take it at night when intestinal transit is slowest, allowing more time for absorption before reaching the colon. 5, 6

3. Ensure adequate hydration and sodium intake, as water and sodium depletion causes secondary hyperaldosteronism, which increases urinary magnesium losses and may necessitate higher oral doses. 5, 2

4. Consider switching to magnesium chloride capsules if bisglycinate continues to cause problems, as these dissolve in stomach acid and may be better absorbed. 2

Critical Safety Consideration

Avoid all magnesium supplementation if creatinine clearance is less than 20 mL/min due to the risk of life-threatening hypermagnesemia, as the kidneys cannot adequately excrete excess magnesium. 1, 6, 2

Common Pitfall

Paradoxically, excessive magnesium ingestion that causes massive diarrhea can actually lead to hypomagnesemia due to excessive fecal magnesium losses. 7 This has been documented with magnesium hydroxide overdose, where the resulting severe diarrhea causes net magnesium depletion despite the large oral intake. 7