I just wanted to add this as a reference to things that cause problems with thyroid. Its very technical. But I think one thing people on this message forum should note is:
Starvation and Fasting
Multiple alterations in thyroid hormone regulation and metabolism have been noted during caloric restriction. The most dramatic effect is a decrease in the serum TT3 within 24-48 hours of the initiation of fasting.36-40b Because changes in the free T3 fraction are usually small, the absolute concentration of FT3 is also reduced, clearly into the hypothyroid range The marked reduction in serum T3 is caused by a reduction in its generation from T4 rather than by an acceleration in its metabolic clearance rate.41,42 The decline in T3 concentration is accompanied by a concomitant and reciprocal change in the concentration of total and free rT3. The increase in the serum rT3 concentration tends to begin later and to return to normal at the time serum T3 is being maintained at a low level with continuous calorie deprivation.38,39 Little change occurs in the concentrations of TT4 and FT4 and the production and metabolic clearance rates of T4.38,39,41,42 When small changes have been observed, they were generally in the direction of an increase in the FT4 concentration. They are attributed to decreased concentration of the carrier proteins in serum, as well as to their diminished association with the hormone caused by the inhibitory effect of free fatty acids (FFA) the level of which increases during fasting.40,43
Ok, that describes the underlying cause of what happens. This is the problem I had. My body had plenty of FT4 but it wasn't properly converting it to FT3. However, why? I wasn't starving myself.... I was following Atkins, probably eating an average of 20-40 net carbs a day.
When I read this, I had an "ah ha!" moment.
Composition of the diet rather than reduction in the total calorie intake seems to determine the occurrence of decreased T3 generation in peripheral tissues during food deprivation. The dietary content of carbohydrate appears to be the key ingredient since as little as 50 g glucose reverses toward normal the fast-induced changes in T3 and rT3.52 Replacement of dietary carbohydrate with fat results in changes typical of starvation.39,53 Refeeding of protein may partially improve the rate of T3 generation, but the protein may be acting as a source of glucose through gluconeogenesis.54 Yet, dietary glucose is not the sole agent responsible for all changes in iodothyronine metabolism associated with starvation. For example, the increase in serum rT3 concentration may not be solely dependent on carbohydrate deprivation since a pure protein diet partially restores the level of rT3 but not that of T339 (Fig. 5-1). The composition of the antecedent diet also has an effect on the magnitude of the serum T3 fall during fasting.39,52 It is possible that the cytoplasmic redox state, measured in terms of the lactate/pyruvate ratio rather than glucose itself, regulates the rate of deiodinative pathways of iodothyronines.55
Well, there you go.
A couple of things to note, eating plenty of protein helps to counter this problem because the protein CAN be converted into glucose.
Keeping your carbohydrates in a higher range, since refeeding of protein alone can't restore all the thyroid juices.
How much do you need? Well, they said 50g of glucose. So I think if you keep your net carbs at 50g or above, you'll be fine. Now don't count fiber because you don't digest it, I also wouldn't count sugar alcohols, I don't really know if carbs digested in the way SA's are digested would really affect your blood glucose.
What if you're taking exogenous thyroid with T3? Well, my feeling is you won't have to worry about converting T4 into T3 so you can low carb or low calorie and not have that concern. However, I wonder if perhaps at the level of cells receiving the thyroid, if perhaps there might be changes there? Could the cells lose receptors when they feel the need to down regulate? Could they become busy with inactive thyroid stuff? Sort of like shoving a broken key in a door, you can't unlock the door (cell), but you also can't stick another key (T3 molecule) in there. I just don't know. From my own experience, I've had to increase my thyroid dose when I'm dieting or I start to feel sleepy and tired all the time. But it might just be my dose wasn't optimal to start with... which I suspect is true. Why would that counteract broken keys? I suspect it changes the ratio of broken keys to working keys, so that there are more working keys in the blood compared to broken keys. But I'm pulling this out of my butt, I may be totally wrong.
I'm actually following a diet right now that is both low carb and low calorie, but it has breaks and periodic high-carb refeeds.
My basic advice for low carbers coming to this forum because they suspect their thyroid is getting wonky is... try to raise your carb levels. See if your brain fog, coldness, sleepiness, hair loss, lack of weight loss improves.
After 2.5 years of low carbing it wasn't that difficult and it didn't reawaken massive cravings in me. I added carbs like yams and apples and beans. If I had added carbs like cake and ice cream, sure, it would have restarted my vicious cycle of cravings again.