The recognizable symptom profiles of low sodium, potassium, and magnesium — the depletion that fasting can provoke.
What the evidence says
- Low sodium (hyponatremia) presents with headache, fatigue, nausea, confusion, and irritability — the cluster commonly labeled “keto flu” or “fasting flu”[1]
- Low potassium (hypokalemia) presents in mild form with constipation, fatigue, muscle weakness, and malaise; more severe deficiency adds muscular paralysis, poor respiration, and cardiac arrhythmias (especially with underlying heart disease), which can be dangerous[2]
- Low magnesium (hypomagnesemia) presents early with loss of appetite, nausea, fatigue, and weakness; as it worsens, numbness or tingling, muscle contractions and cramps, and abnormal heart rhythms can appear[3]
- Muscle cramps and fatigue are common to more than one deficiency, so symptoms alone do not identify which electrolyte is low[2],[3]