This is an important study because it shows the effect of pursuing low-calorie diets on thyroid.
You might recall that the thyroid hormone controls the master switch to metabolism and entire body.
If the thyroid is low, metabolism is low. Low metabolism means that you gain weight easily, and lose with great difficulty. It also leads to a higher rate of heart attacks, sexual dysfunction, and compromised immune system. Not to mention low mood, depression, and difficulty doing physical exercise and maintaining normal activity levels.
This is a very important study because they evaluated the effects of low-calorie diets and no carb diets in normal subjects.
Let’s talk about T-3 versus reverse T3
T-3 is the most active form of thyroid hormone. Your body makes T4, and T4 kind of stores thyroid hormone in a less active form. When your body needs immediate thyroid, it converts some of that T4 into T-3. T-3 is immediately used. If you take T-3, you get an immediate effect. Your heart rate will go up, your temperature will normally go up a little bit, and you’ll feel pretty good. T-3 lasts maybe 3 to 5 hours in the body. Your body is continually making T-3 out of D4 if you have a normal thyroid function.
T-3 is made mostly in the liver from T4. So if you have fatty liver, as most people do, you may not be very good at converting T4 into T-3. And so you may be hypothyroid.
Okay, so thyroid is so important that your body also has a kind of thyroid neutralizer. This is called reverse T-3, or RT three. RT three neutralizes the thyroid receptors in Excel. It kind of jams up the receptors.
If you have too much thyroid, your body will produce reverse T-3, to jam up the receptors in the cells, and neutralize the effects of too much thyroid.
In this study, they found that total fasting causes high levels of reverse T-3. Essentially, if you fast, your thyroid shuts down.
However, for people on a low-calorie diet, as opposed to total fasting, their T-3 went way down, but their body did not produce reverse T-3. So they ended up with low thyroid function, but they were not completely neutralized. They were still getting thyroid in their cells. Even though the amounts were much smaller.
The kicker has to do with carbohydrates and dieting
The big shocker is that for people with low-calorie diets who were getting some carbohydrates, their T-3 and the reverse T-3 remained at normal levels.
The only thing that maintained thyroid levels during low-calorie dieting was sufficient carbohydrates.
The takeaway from this study is that if you are going to pursue dieting, you should maintain adequate levels of carbohydrates. If you don’t, your thyroid function is going to suffer greatly.
And it’s not clear when thyroid levels returned to normal. They probably return to normal fairly quickly, in a normal person with a good liver that is good at converting T4 and T3.
But this is an indication as to why low-carb diets often do not succeed.
They lower thyroid function, which lowers metabolism, and that means that you are not burning nearly as many calories while you are on a low-carb diet as you would otherwise.
EFFECT OF CALORIC RESTRICTION AND DIETARY COMPOSITION ON SERUM T3 AND REVERSE T3 IN MAN