Ya know, just reading this article gives me a good opinion of Harris' insight. It's only when i read his comments on other blogs that he irritates the hell out of me.
Speaking of the components of our diets in terms of macronutrients IS bullshit. To put corn oil and red palm oil in the same category is just plain ignorant. To equate tryptophan, tyrosine, taurine and glycine, ditto. And to compare whole-wheat flour and swiss chard (silver-beet to my international friends) is madness.
The evidence, then, that i hoped to show Sidereal is eluding me right now; i can only pass on the bare "fact" and save the discussion for a later day. :-( A rodent study looked specifically at how different dietary fats affected thyroid use in tissues. The "receptivity" of the cells was best in the presence of saturated fats, lower with monounsaturates, and SIGNIFICANTLY poorer when those hearthealthypolyunsaturates were fed.
It hardly matters how much T3 is in your blood, if it can't get into the tissues to work!
And again -- your starting point determines how much improvement you'll see when you make a dietary change. I suspect this is why some people feel they get a metabolic boost from coconut oil while i never observed it particularly. If you go from a high-omega6 "SAD" or Atkins diet straight to CO, yes -- i imagine you'll get a huge boost. I came to LCHF via Atkins, but have never been a fan of vegetable oils. I started using butter, olive oil and bacon drippings when i abandoned low-fat, and so the metabolic advantage i experienced with the lowered sugar and starch, and the raised saturated and monounsaturated fats came all at once.
I feel that my thyroid production, conversion and usage are optimal when i'm getting LOTS of grassfed beef and lamb fat. I feel GOOD when i fast (ie, my body is burning my own stored saturated fat), but the reduced food intake causes my body to downshift my thyroid.
I think this is where a lot of people get confused! A LCHF diet reduces the appetite, because one gains access to one's own fat for fuel, BUT the body senses a reduction in intake whether it be via leptin, FIAF or something else, i don't know. The "food scarcity" signal lowers thyroid production.
It is NOT that "low-carb reduces thyroid function" -- I CAN'T SAY THIS ENOUGH!!! It's that an "underfed" body lowers thyroid production. A carb-fed body requires more thyroid hormone to burn that potentially-harmful fuel flooding the bloodstream, so a euthyroid individual ramps up production. An individual with a "weak" thyroid may not be able to meet the challenge. THIS is why a low-carb-high-SATURATED-fat diet is so important to my well-being.