Thyroid Physiology and Negative Feedback

This week in The Metabolic Classroom, Ben explores the effects of a ketogenic diet on thyroid function, addressing concerns that lower thyroid hormone levels observed during the diet may indicate dysfunction.

Dr. Bikman begins by explaining the hypothalamic-pituitary-thyroid (HPT) axis, a regulatory system that controls thyroid hormone production. The thyroid gland produces two primary hormones, T3 (triiodothyronine) and T4 (thyroxine), with T3 being the active form that influences metabolic processes. He emphasizes the concept of negative feedback within the HPT axis, explaining that normal TSH levels generally indicate a well-functioning thyroid, even if T3 levels are lower.

Ben also reviews a commonly cited study that observed decreased T3 levels in individuals following a ketogenic diet. Despite the drop in T3, TSH levels remained normal, suggesting that the thyroid gland was not damaged but rather adapting to reduced metabolic demand. He introduces two key explanations: improved thyroid hormone sensitivity and reduced glucose metabolism. Improved sensitivity means that lower levels of T3 are sufficient to maintain metabolic functions, while reduced glucose consumption on a ketogenic diet lessens the body’s need for thyroid hormone to regulate glucose uptake.

The classroom lecture then delves into the concept of thyroid hormone resistance, a condition linked to metabolic disorders like obesity and type 2 diabetes. Dr. Bikman references studies showing that thyroid resistance is real and measurable, often associated with elevated TSH and thyroid hormones in individuals with metabolic syndrome. He speculates that a ketogenic diet may enhance thyroid sensitivity in these individuals, reducing the need for higher T3 levels.

In conclusion, Dr. Bikman reassures those on a ketogenic diet that lower T3 levels do not necessarily indicate harm. If TSH levels are normal and no symptoms of hypothyroidism are present, the changes may reflect a healthy adaptation to the metabolic state induced by the diet.

Show Notes/References:

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