Impact of Diet and Calorie Restriction on TSH Levels in Hypothyroidism

James Hennessey, MD, FACP: Now, obviously, there are other things that will lower the TSH [thyrotropin levels] results, and metformin is one of them, but I've never seen anyone treated with metformin that had a suppressed TSH. It’s just slightly low, but not clinically significant.

Antonio Bianco, MD, PhD: I saw many patients who are on a diet —everyone’s trying to lose weight—and once they restrict their caloric intake, that lowers serum TSH, and not only serum TSH. Sometimes I get a referral patient with low serum T3 levels and low TSH, but very low T3s, and at first, I think it is due to mutations in the adenase, but that’s not the case. Often those patients were on a low-calorie diet.That is something that will prevent TSH from going up while causing T3 levels to go down. That might present as a puzzle for most clinicians, but correlating with caloric intake, I think that’s important information.

James Hennessey, MD, FACP: Absolutely. Your observation is quite accurate. I recall when I was a fellow, watching Jen Berman do a study of patients who were being admitted to The Walter Reed Army Medical Center (WRAMC) for fasting protocols because they were overweight. One of the initial people who demonstrated this dynamic of the T3 levels dropping down, and his theory, which I think is true, is that the body tries to conserve energy when little food is coming in; therefore, we observe this decrease in the T3. [Salman] Razvi, [Newcastle University] reminds us…. that in the first-trimester of pregnancy, TSH tends to be low. African American ethnicity [can contribute to] lower TSH, but not dramatically. Dopamine agonists, glucocorticoids, retinoids, and interferon all can be associated with lower TSH.

Transcript edited for clarity