Carbohydrate Overfeeding Increased Serum T3 By 42%

Giraffe

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Decreased free fraction of serum thyroid hormones during carbohydrate overfeeding.

Abstract

The impact of the increased T3 production induced by overfeeding is likely to be lessened if overfeeding also decreases the free fraction of thyroid hormones. Therefore, we examined the effect of 17 to 20 days of carbohydrate overfeeding of five men on total serum T4 and T3 concentrations, the free fraction of these hormones, and serum concentrations of thyroid-hormone binding proteins, TBG, TBPA, and albumin. Total serum T4 concentrations were unchanged by overfeeding and total serum T3 concentrations increased 42%. However, the free fraction of both T4 and T3 decreased during the overfeeding period, so that free T3 concentrations increased only 21% and free T4 concentrations decreased 17%. There was an increase in serum concentrations of both TBG (12%) and TBPA (20%), but no change in the concentration of albumin. We conclude that there is an increase in free T3 concentrations during overfeeding, in spite of a decrease in the free fraction of T3. However, the physiological effects of this increase in free T3 concentrations may be diminished by the decrease in free T4 concentrations.


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Thyroid hormones are hydrophobic, so most of them are bound to proteins etc. Only a tiny fraction of the thyroid hormones is unbound (the so-called "free" hormones). Contrary to the mainstream opinion Ray Peat says that the total amount of thyroid hormones matters, not the "free" fraction (it's not true that only the "free" hormones are the active ones).

Also see topics:

The influence of free fatty acids on the free fraction of thyroid hormones in serum as estimated by ultrafiltration.
Low calorie, low carb intake lowers T3 and increases rT3
 

tara

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Mar 29, 2014
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:)
 

mujuro

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Nov 14, 2014
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T3 also increase SHBG, no? Another binding protein commonly and incorrectly viewed as a negative marker.
 

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