Magnesium: The Most Overlooked Fasting Supplement

How Common Is Deficiency?

Estimates suggest that roughly 50% of the general US population does not meet the recommended daily intake for magnesium from diet alone — and this is without fasting. Fasting increases urinary magnesium excretion, compounding an already widespread deficiency. This makes magnesium the single most impactful supplement for the majority of fasters.

What Magnesium Deficiency Feels Like

The symptoms of low magnesium overlap significantly with common fasting complaints: muscle cramps (especially at night), difficulty sleeping, anxiety, headaches, fatigue, constipation, and irregular heartbeat. If you are experiencing these and are unsure if fasting is causing them, magnesium deficiency is worth addressing first.

Which Form to Take

Not all magnesium supplements are equal. Magnesium oxide (the cheapest and most common) is poorly absorbed — roughly 4% absorption. Magnesium glycinate is highly bioavailable, well-tolerated by the digestive system, and the best all-around choice for most people. Magnesium malate is good for energy and muscle recovery. Magnesium citrate is effective but has a laxative effect in higher doses. Start with magnesium glycinate at 200–400mg before bed.

Timing

Taking magnesium at night is ideal — it does not break a fast, and it supports the deep sleep that fasting enhances. Many people notice improved sleep quality within a week of consistent supplementation. Do not take magnesium with zinc supplements (they compete for absorption).

Food Sources

Dark leafy greens (spinach, Swiss chard), almonds, pumpkin seeds, avocado, and dark chocolate are excellent food sources to prioritize in your eating window. But given how common magnesium depletion is, supplementation is a reliable insurance policy regardless of diet quality.

See also

• Electrolytes Explained
• Potassium and Fasting
• Sodium During Fasting