Premature thelarche in an infant girl with failure to thrive related to dietary soy exposure.

A 7-month-old female infant presented with failure to thrive. She was breastfed till 3 months of age, thereafter switched to soy-based milk formula. There was no history to suggest excess energy losses, recurrent infections or chronic diarrhoea. Three months after switching to exclusive soy-based milk formula, parents noticed significant enlargement of both breasts. Clinical examination was unremarkable except for enlargement of both breasts. None of the other secondary sexual characteristics were present. Initial blood investigations showed hyponatraemic hypokalaemic hypochloraemic metabolic alkalosis, which corrected after 2 days with intravenous hydration. The patient subsequently maintained normal electrolyte balance with recommended intake of cow's milk-based standard formula milk.Further exploration of her soy-based milk revealed that it was low in sodium and calories, unsuitable for children. This was not a standard and approved infant soy-based formula milk. She achieved excellent weight gain and reduction of breast size on cessation of soy-based milk formula.