When i first heard of "thyroid resistance" (as compared with that of insulin or leptin, for instance), i thought it might be a made-up malady, just like "restless leg syndrome." It subsequently occurred to me that it might simply be the perceived lack of function which comes with excessive O6 intake ... because the latter DOES interfere with thyroid receptors.
Googling "linoleic acid interferes with thyroid receptors" will produce a plethora of hits, ranging in credibility from PubMed to jock-blogs. The concept is neither new nor terribly controversial (though there's always reason to question in-vitro rat studies). So why do we hear so little about it? Until i found the concept (buried in an old book review by Chris Masterjohn), the closest i'd come to learning this was reading "saturated fat in the diet is good for thyroid function." ...I love how so many sites state absolutes like this without any kind of reasoning or discussion....
Considering this, it's no wonder some people feel crappy on a low-carb diet -- they're doing it wrong (and god rest Dr. Atkins, but he told them to). Yes, i DID just say THEY'RE DOING IT WRONG, and i meant it. Much as i dislike the blame-the-victim mentality implied by those words, it IS possible that a lot of failure in the LC world has to do with mistakes that can be pure innocence or outrageous stupidity (like getting one's few allowed carbs from CANDY, like one outspoken "anti" did).
We NEED our saturated fats, BECAUSE those seem to be the best choice for thyroid-challenged people in maximizing function. Monounsaturates are better than polys, but still inhibitive. And we need fats, in general, because it BOOSTS CALORIE INTAKE, which is GOOD for our thyroid function*! Learning this, i'm beginning to rethink my strategy in making mayo and other salad dressings. I love a good olive oil, and ditto for avocado, but hey -- certain things (like well-being) are more important than others.
It becomes important for hypothyroids, even if they're not low-carbers, to avoid omega-6 fats to the best of their ability -- because they're ubiquitous. EVERY time you dine out, you ARE getting linoleic acid, no matter what you eat. It's in your meat, your eggs, your cheese, your fish, your coffee-creamer, your vegetables, your ice-cream and ronaldmcdonald only knows what else! In our beloved grass-fed beef and lamb, it still comprises a significant amount of the fat involved, though in better proportion than in CAFO meat ... and there's also a goodly amount of thyroid-inhibiting monounsaturates in there. Among our best friends, ironically, are the fruit-based oils such as coconut and red palm, and palm-kernel (SEED!), and their artificially-isolated cousin, MCT.
Eating a low-carb diet is soothing to a hypothyroid, because the less dietary glucose we have to dispose of, the farther our limited supply of hormone will go. People who claim that it's "stressful" to us aren't looking at the big picture. However, we absolutely positively MUST do it correctly, by minimizing disruptive poly- and monounsaturated fats, and maximizing all those heart-healthy SATURATED fats we've come to love!
(And by getting our allowed carbohydrate intake from a garnish of low-starch, low-fructose, low-toxin vegetables instead of from a chocolate box.)
* nothing seems to inhibit even normal thyroid function like calorie-restriction!