The accusation which one has heard a lot through the years by people who hate LC is that it "destroys" the thyroid. One particularly virulent hater, who actually had good luck with it before the mating-call of the wild truffle lured her back to orthodoxy, not only claimed her thyroid was fried but accused LC of bringing on premature menopause. GOK what she must have been doing, to upset her hormones that much! But she wasn't alone -- the gym-rats also chimed in agreement: "the thyroid NEEEEEDS carbs," they scream. "Just look at my lab test!" Those guys must spend half their disposable income getting blood drawn and analyzed.
The ironic thing is that in replacement of the classic Atkins regimen, the people under discussion advocate the very thing GUARANTEED to wreck your metabolism: that tired old ELMM routine, which Dr. Fung excoriates HERE.
Repeat after me: anything that makes the body fear starvation is going to lower metabolism to preserve body-resources including fat. The means of doing so are via the thyroid; increasing rT3 is a mechanism the body uses to MAKE you feel tired so you won't waste fuel or dilute your healing-energy. We heal while we rest and sleep, and surgery-patients need to concentrate their bodies' resources on reknitting tissues and fighting infections -- that's why their thyroid levels dip. If your body thinks that starvation is imminent, it's going to let your hands and feet get cold, rather than squander precious resources just so you'll be comfortable.
Of course, this does NOT mean your thyroid is "destroyed" -- not even close.
The bro's point to their lab-test numbers, but don't experience classic hypothyroidism SYMPTOMS. The LC dieters -- AND ELMM dieters -- wave their chilly fingers in your face, but feed them ONE sufficient-energy meal and they're all-of-a-sudden warm and cozy again. You can believe me on this: i know my hypo symptoms, and they're not only exceptionally diverse, but also brought on by lots of different causes.
I know i've said it a myriad of times, but it won't hurt to point out just once more: lower T3 in a low-carber is not hypothyroidism -- it doesn't coexist with higher TSH, and if that's "normal" the body doesn't perceive a requirement for more T. The body requires active thyroid-hormone to process carbohydrates in the diet; if they're not there, the body produces less of T3 and TSH, because it doesn't NEED as much.
Hell, I can tell a difference in my body's performance, depending on whether I've had enough sat-fat in my diet, or too much PUFA on a particular day. The body reacts to some really "minor" stuff -- in the case of fats, it's not conversion but cell receptors.
As Dr. Rosedale is fond of pointing out, a higher baseline thyroid reading is NOT a good thing in a euthyroid individual -- it means the body is "running hot" and in danger of "burning out" sooner. His schtick is longevity, and has made it a point to learn that centenarians tend to run on the low end of the normal range.
Dr. Donaldson, in "Strong Medicine," makes a point of discussing thyroid hormone in weight loss, debunking a popular myth:
At times thyroid extract can increase the cooking flame in the body, just as new sparkplugs may increase the efficiency of an automobile engine. It used to be thought that feeding it in small quantities might help to burn off excess body weight. With the exception of about four per cent, that happened regularly to people with the disease called exophthalmic goiter. They would usually melt away under the load of too much thyroid hormone in the blood. But it didn't work in simple obesity. Because so many thousands of fat people still uselessly take thyroid extract to lose weight, the subject needs to be more generally under stood."Prescribing unnecessary thyroid supplements used to be a tweak for weight-loss, but it fell out of favor because it's HARMFUL. I remember Muhammed Ali using the stuff in the course of his career. The practice was replaced by prescribing "diet pills" -- uppers -- instead....
"Excess weight" is just another subject on which Nature and Society don't mesh. Nature seems to favor a little bit, as being a kind of life-insurance policy, whereas our modern world looks on it as nothing but bad, ugly, and indicative of an inferior character. Too bad: as we age -- which is when Nature schemes to make us gain weight -- a little extra adiposity can mean the difference between surviving an illness or injury, and succumbing to it. If we look at it in the traditionally-sentimental way, Nature wants us to put on fat in the autumn of our lives, so that in winter we can hang on just a little longer.
Many different causes are responsible for thyroid-hormone fluctuations in a perfectly-healthy individual. We should look on them as feedback for what we're doing to ourselves, not panic and scream "this diet DESTROYED my thyroid!"