 An optional sub-study is being made available to research subjects to compare the stool microbiota longitudinally, with the initial stool sample at the start of the study in the presence of normal systemic thyroid hormone levels and then again after thyroidectomy while taking oral levothyroxine. Comparisons of any microbiota compositional changes from before and after surgery will be made to any changes in symptoms, cognitionmemory testing and overall quality of life. Any exposure to antibiotics, probiotics or other updates to medical history will be documented at each visit. Any exposure to systemic antibiotics in the previous 60 days of the first study collection or between collections will be excluded. Subjects will complete a 3-day lead-in dietary log prior to each stool collection, summarizing meal compositions on 3 consecutive days before the stool sample is collected and submitted. Participants will be given their own dietary log again and encouraged to follow a similar diet prior to the second stool collection. 