What is T2, and why have researchers been investigating its effects on metabolism?
In this episode of the Optimal Protein Podcast, I'm welcoming back Dr. Amie Hornaman to explore 3,5-diiodothyronine, commonly called T2—a lesser-known thyroid hormone derivative studied for its effects on energy expenditure, fatty acid oxidation, and mitochondrial function.
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We walk through research on liver cells, skeletal muscle, and brown fat, unpacking the machinery that helps fatty acids enter the mitochondria and a process called mitochondrial uncoupling, in which energy is released as heat.
We also explore possible connections with ketogenic diets and the question that matters so much to us here: what could these findings mean for losing body fat while preserving muscle?
Much of the research discussed comes from animal studies. We examine a small human report involving just two participants, and Amie shares observations from an uncontrolled group of 14 women who used her T2-containing product. These findings raise interesting questions, but they do not establish that supplemental T2 is a safe or effective approach to fat loss.
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In this episode, we discuss:
Important context for interpreting the research
The approximately 50% lower fat mass reported in the 2005 rat study was a comparison with the untreated high-fat-diet group. It does not mean the animals lost half of their starting body fat.
The 2011 human report described approximately 4% lower body weight, not proof that all weight lost was fat. Neither that report nor the uncontrolled 14-woman project establishes long-term safety or that T2 caused the reported changes.
Changes in muscle-cell fuel use do not establish muscle preservation during weight loss. Shared metabolic pathways also do not establish that combining keto and T2 provides additional benefits.
Studies discussed
Additional safety references
Thank you so much for listening! If you enjoyed exploring the science with us, please share this episode with a friend who loves learning about metabolism and body composition.
Join me on Friday for my solocast recap, where I'll revisit the key mechanisms, clarify what the studies do and don't show, and connect the discussion to practical takeaways for supporting muscle and metabolic health.
Guest disclosure and medical disclaimer
Dr. Amie Hornaman sells the T2-containing supplement discussed. This episode is educational and does not endorse or recommend purchasing or taking it. Some animal studies have raised concerns about thyroid suppression and heart effects; availability without a prescription does not establish safety.
Do not start T2, substitute it for prescribed treatment, or change your thyroid medication based on this episode. Consult a qualified healthcare professional about your individual circumstances.
Correction: In the mitochondrial uncoupling discussion, we meant DNP, not DMT.