I did a Doctor’s Data test on a 12-year-old patient referred to me because she is very underweight. All the markers on the test are normal, including 3s or 4s for all the beneficial bacteria with the exception of having few microscopic yeast and a stool pH of 5.8. The question is whether you would treat the yeast and what the significance of the low stool pH is?

Chris Kresser:  Yes, I would probably treat the yeast because this patient may be malabsorbing nutrients and calories. A low fecal pH is a sign of fungal overgrowth or other dysbiotic conditions. This is another situation where we would make a clinical judgment call, and even though the fungal overgrowth wasn’t moderate or many, it is still outside of what would be considered normal. Fungal overgrowth could cause the underweight symptom that you mentioned. I would also consider the patient’s history. If she has a history of multiple courses of antibiotics throughout her childhood and other symptoms that are consistent with fungal overgrowth such as skin breakouts, rashes, acne, fatigue, brain fog, gas, bloating, GI symptoms, all that sort of stuff. That would strengthen my conviction to do a therapeutic trial.