A ovolactovegetarian patient presented with hyponatremia. She had maximally dilute urine and undetectable vasopressin levels. Dietary history revealed very low protein intake but no beer intake. We postulated that the very low intake of solute limited her water excretion and caused the hyponatremia despite only a modest increase in fluid intake. When protein intake was increased in a clinical research center setting, free water excretion increased and serum sodium normalized despite maintaining the water intake at 4 to 5 L daily. We discuss the role of dietary solute in water excretion. Previously described in beer drinkers, the phenomenon can occur in the absence of beer drinking. In this era of weight consciousness, hyponatremia because of low solute intake may be seen with increased frequency.