Sir.—We read with interest the letter by Arden et al1 on the association of alkaline urine with eating disorders. Seventeen (37%) of 46 patients with eating disorders had an alkaline urine pH compared with only one (4%) of 28 control subjects. Arden et al suggest a number of possible causes of the alkaline urine pH, including self-induced vomiting, "alkaline tide," diet, osteoporosis from estrogen deficiency, and hypochloremic alkalosis due to diuretic or laxative abuse. Several of these causes would not explain an alkaline urine pH. Chronic, self-induced vomiting and diuretic or laxative abuse are usually associated with mild extracellular fluid volume contraction and an acid urine pH. This aciduria, referred to as "paradoxical aciduria" when a metabolic alkalosis is present, develops consequent to secretion of a hydrogen ion in the distal nephron when a sodium ion is reabsorbed to replenish the volume of extracellular fluid.
The evaluation of the