Does magnesium break a fast?

Magnesium supplements, such as magnesium citrate, glycinate and oxide, are a mineral salt in a tablet, capsule or powder. A plain tablet or capsule has almost no calories and no sugar. It keeps a fast intact for all four of this site's goals: weight loss, autophagy, gut rest and blood sugar.

Adults aged 19 to 64 need about 300 mg of magnesium a day (men) or 270 mg (women). Spinach, nuts and wholemeal bread are good food sources, and a varied diet should give you all you need. If you take a supplement, 400 mg or less a day from supplements is unlikely to cause harm. Higher doses over a short time can cause diarrhoea.

Some people take magnesium on longer fasts or in the evening. The evidence that it helps sleep is limited. A review of trials found magnesium unlikely to prevent muscle cramps in older adults.

Powders and drinks are where a fast can slip. If a magnesium powder is flavoured, check its label for sugar and calories. An electrolyte mix with sugar or dextrose breaks a fast for blood sugar, autophagy and gut rest. A mix with sweetener and no sugar is a grey area for blood sugar and autophagy.

If you take magnesium for a fasting headache, it helps to know that doctors recognise fasting headache as its own type. It usually eases after eating, and its exact cause is not known.

Do you have kidney disease, high blood pressure or heart failure, or take water tablets or potassium supplements? Then ask your doctor before adding minerals such as salt or potassium during a fast.