Thyroid Hormones and Weight Loss
What is the relationship between thyroid hormones and weight loss?Although these are not the only hormones involved in weight regulation, this article may help you to better understand the adaptations that occur during periods of prolonged dieting.
The main thyroid hormones that you should know about are T3 and T4 (the full names are not important here), and both of them are secreted by the thyroid gland in a ratio of roughly 1/4.
(More T3 is produced in liver and other tissues by removing one of the iodine molecules from T4.)
It's important to note that T3 plays a major role in regulating metabolic rate (by mediating the rate at which tissues use fuel), and this is seen specially during dieting when the conversion from T4 to T3 is severely reduced.
However, just taking thyroid drugs doesn't fix all the problems because, as mentioned, other hormones influence as well the adaptations that occur under a prolonged calorie deficit.
One way to improve thyroid conversion is doing high intensity exercise because this will greatly stimulate adrenaline and noradrenaline.
This will determine an increase in T3, which will further stimulate catecholamines because these hormones are interconnected. One effect of this synergy is that when thyroid is low, lipolysis is reduced because adrenaline and noradrenaline are inhibited.
It's worth mentioning that people with low thyroid show an impaired blood flow to their adipose tissue, which makes fat mobilization more difficult. This may explain why is so much harder to diet at low body fat levels.
However, artificially increasing thyroid above normal physiological levels may do more harm than good because it could affect negatively muscle mass.
So what happens with these hormones and weight loss when dieting? Gradually, more and more fatty acids will get into the bloodstream, and this will eventually obstruct T4 uptake into the liver, which also has an effect on lowering the T3.
Furthermore, cortisol levels will increase, which will inhibit the enzyme responsible for mediating the thyroid conversion. (This enzyme has a weird name that I can't even pronounce. It's called “deiodinase”.)
The best way to reverse the above adaptations is to take longer diet breaks (at least one week). Calories should be increased to maintenance, and you should consume at least 100-150 grams of carbohydrates.
As a side note, this strategy concerns the individuals who are dieting for long periods, and need to reset their T3 levels. If you suffer of hypothyroidism, which is due to a malfunctioning of the thyroid gland, you should consult a medical doctor.
People who normally have low thyroid levels (especially women) could also consider a synthetic drug (Cytomel is the most common) or natural compounds (such as Armour) to increase their T3 to an optimum level.
Also, it seems that ephedrine may improve T4 to T3 conversion, but in my opinion the safest and most practical way to achieve that is to take a diet break as noted above.
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