Thyroid Hormone Sets the Tempo
Thyroid hormone drives metabolic rate. In overt, untreated hypothyroidism, BMR can drop — estimates suggest roughly 5–15% lower in severe cases, with smaller effects in mild/subclinical disease. That is a modest daily calorie reduction, not a dramatic one.
The Treatment Caveat
Levothyroxine (or equivalent) restores euthyroidism for most people. At that point, standard BMR equations apply — there is no permanent "slow thyroid" after successful treatment, and no special thyroid diet is needed.
Our Hypothyroidism Calculator applies a conservative ~5% BMR reduction only if you mark the untreated/suboptimal state. See hypothyroidism diet and the Hypothyroidism hub.
Educational only. Dose and TSH targets are clinical decisions — never adjust thyroid medication without your clinician.