There are some interesting acid-base perturbations that can take place in the setting of eating disorders and/or surreptitious use of substances used to intentionally lose weight. Due to the surreptitious nature of many of these disorders, some lab & physical exam sleuthwork may be necessary to make the diagnosis.
Self-induced vomiting is a common feature of the eating disorders anorexia nervosa and bulimia. Because these individuals are losing HCl from stomach secretions, it is not uncommon for them to develop a metabolic alkalosis. Sometimes physical exam clues can be important in making this diagnosis: vomiting induced by sticking a finger in the back of one's throat can result in scarring on the dorsum of the hand, the formation of oral ulcers, dental erosions due to chronic gastric acid exposure, and puffy cheeks as a result of salivary gland hypertrophy. Furthermore the urine chloride is often profoundly depleted; this is classically a "chloride-responsive metabolic alkalosis."
Surreptitious diuretic use is also surprisingly common, and metabolic alkalosis is felt to derive from multiple contributing mechanisms: secondary hyperaldosteronism often develops due to volume depletion, renal chloride loss, or a contraction alkalosis; chloride-unresponsiveness may also develop due to a profound K depletion which may result from either chronic thiazide or loop diuretic exposure. Tests which assess the concentration of common diuretics in the urine by chromatography are available and may be necessary to cement the diagnosis.
Surreptitious laxative abuse can result in either a non-anion gap metabolic acidosis (similar to patients with chronic diarrhea) OR a hypochloremic metabolic alkalosis which results from hypokalemia, increased renal bicarbonate reabsorption, and volume contraction due to profound loss of sodium and water in the stool. These patients will often present with a fictitious diarrhea, and is found with greatest frequency in females who are related to the health care field.