"What do you think explains the low potassium if not an eating disorder?"
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Just was searching on google for an answer -- she might have been taking diuretics or one of the other causes listed below could have been responsible:
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"Low Potassium Levels
Question: What can cause potassium levels to remain low even with supplements?
Answer: Potential causes of hypokalemia (a favorite question of third year medical students).
1. GI disorders(vomiting, diarrhea, villous adenoma).
2.Renal causes(alkalosis,mineralocorticoid excess,diuretics,licorce[English not American],Conn's Syndrome, Secondary aldosteronism, different renal tubular diseases),
3. Other causes(excess insulin, familial periodic paralysis).
Basically, if one's potassium is low there is a pathologic cause. GI is the most common or possible diuretic use. If there is no obvious GI loss or diuretics the above causes will need to be looked for."
http://64.233.167.104/search?q=cache:GVmvV5BaApAJ:www.druginfonet.com/index.php%3FpageID%3Dfaq/new/DISEASE_FAQ/Potassium.htm+low+potassium+cause&hl=en