the thyroid scenario...

...Seems to be extraordinarily oversimplified a lot of the time.  One has this image of the gland manufacturing and sending out hormone like a factory responding to orders (TSH) from the head office (pituitary).  Given enough raw materials going in (tyrosine and iodine), you expect your workforce (thyroid gland) to put together and ship whatever the orders called for, and it's up to the customers (body-wide tissues) to take the material (mostly T4, some T3) and further turn them into the finished products they require.  If you have a less-efficient workforce, you may not get as much product from a day's work as you should.  Then if a shipment of raw material doesn't arrive on time, they may work their butts off but will be unable to do the job; and if a shipment of fluoride, bromine or chlorine is mistakenly sent, it can tie up the iodine "loading-dock" while the truck-driver and foreman argue about the debacle....

Actually, this turned out to be a better analogy than i thought it would.  ;-)

It's when the gland's products go out into the world to achieve their life's-work that things get REALLY complicated.  That's what i have only STARTED to explore in my reading these days.  The sheer number of different interactions is mind-numbing.  The first thing that caught my attention:  carbohydrate metabolism.

THYROID HORMONE HELPS INSULIN FERRY GLUCOSE INTO CELLS FOR ENERGY-PRODUCTION.  It promotes more GLUT4 (as well as LDL) receptors.  If there is less glucose in the system to be disposed-of, less thyroid is needed to do the job -- THAT is why you get lower free T3 on a low-carb diet.  You just don't have the requirement; it's not pathological, it's physiological.

We should never forget for a moment that the longer our blood-glucose is high, the more DAMAGE it's inflicting on our organs, nerves and vessels.  Insulin and thyroid are working their asses off to use it up or store it away FAST.  Raising temperature and giving muscles a reason to do their thing are the first choice, but insulin WILL store it as fat if it has to.

When normal quantities of the thyroid hormones are called away from their usual duties to assist insulin in its endless toil, you end up with hypOthyroid symptoms.  A strong healthy thyroid will do its best to make the amount you need, but it can overproduce, too, and hypERthyroidism isn't a good thing, either.  Most people don't supplement tyrosine -- they make it from phenylalanine in the diet with the help of enzymes ... and remember how i said people produce fewer enzymes as they get older?  Add to this iodine-deficient diets* and you have the perfect recipe for a metabolic MESS.

Some time ago, Chris Kresser wrote a good article on the connection between thyroid function and blood-sugar, and more recently, Sam Knox wrote a better one.  Unless you really WANT to think that carbs in your diet are a good thing for your thyroid, i don't know how you can avoid coming to the same conclusion i did -- that MY thyroid is MUCH healthier and happier on LCHF.

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* most people think that they'll get plenty of iodine from salty foods, not knowing that commercial foods are usually made with NONiodized salt.