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How do thyroid hormones affect weight?
Last reviewed: 04.07.2025

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The thyroid gland in women is strikingly different from that of men - at least in that malfunctions of the former occur 10-20 times more often than in men. According to statistics, thyroiditis (thyroid disease) affects women 25 times more often than the stronger sex.
Thyroid gland under the sight of hormones
After 40 years and up to 65 years, the risk of thyroid diseases increases for both men and women. However, thyroiditis still occurs more often in women of this age than in the strong half of humanity.
It should be known that all types of thyroiditis (bacterial, viral, postpartum, toxic and others) contribute to the development of antibodies that have the ability to destroy thyroid tissue.
Or another unpleasant property of thyroiditis: it can provoke the destruction of hormones produced by the thyroid gland.
How does the thyroid gland get destroyed?
During the course of thyroiditis, the body produces antibodies - substances that interfere with the work of hormones. Therefore, all functions of the thyroid gland are at risk.
Antibodies can start acting long before the thyroid gland can produce protective hormones. And then the woman experiences unpleasant symptoms typical of thyroid diseases for a very long time. This can be several years.
Overweight women are at greater risk
The greatest number of antibodies that interfere with the thyroid gland are observed in women who are overweight. This leads to major and not the best consequences: slowing down of metabolism, accumulation of fatty tissue, destruction of muscle tissue and, of course, even more weight gain.
All these unpleasant consequences can be accompanied by severe muscle pain. Doctors call this condition myalgia. Based on these symptoms, a woman can determine that her thyroid hormones are out of order and the antibodies are too active.
In Norway in 1996, studies were conducted that proved that the greatest increase in the number of antibodies was observed by doctors in women who complained of muscle pain and at the same time gained weight. No such symptoms were found in men.
Doctors have concluded that when treating such women, it is worth paying more attention to antibodies - much more than to the work of the entire thyroid gland. That is, first of all, women with such symptoms should have their thyroid hormones and antibodies checked. Then they can be prescribed the optimal treatment.
What can baffle women when it comes to diagnosis? A woman can check her body with hormonal tests and find out that she has an imbalance of thyroid hormones. And… hear from her doctor that her extra pounds are not related to the thyroid gland.
This is extremely surprising for a woman who may have already read somewhere that thyroid disease – hypothyroidism – is associated with the problem of excess weight. The reason is an increase in appetite due to an increased level of thyroid hormones.
Without having your hormones checked, it’s hard to imagine that all your problems with excess weight are due to this, and not to your lack of discipline and addiction to sweets.
If the doctor doesn’t listen to you, recommends simply keeping your mouth shut from all kinds of tasty treats and doing sports, and doesn’t even remember about hormonal tests, do them anyway – on the recommendation of another doctor.
What are the risks of thyroid disease?
- Irregular menstruation - sometimes scanty, sometimes heavy, and always at the wrong time
- Infertility
- Depression
- Chronic fatigue syndrome
- PMS syndrome
- Increased cholesterol levels
- Impaired glucose tolerance
- Fibromyalgia (muscle pain plus weight gain)
But doctors and patients themselves may associate these symptoms with mental disorders and not at all with thyroid disease.
Patients are prescribed psychotropic drugs, which only worsen all these symptoms, increasing appetite. At worst, the medications simply do not help.
Research shows that mentally unstable patients sooner or later suffered from thyroid disorders. And it was these diseases that provoked excess weight gain and depressive states.
It is important to have hormonal tests at least once a year, because the risk of developing thyroid disease increases with age. Therefore, if routine tests show that the thyroid gland is functioning normally, additional tests should be performed.
Thyroid hormones: T3 and T4
These are the main hormones produced by the thyroid gland, a small butterfly-shaped organ located just above the Adam's apple. T3 stands for triiodothyronine, and T4 stands for thyroxine.
These hormones are important substances for regulating metabolism. They help tissues and cells to be saturated with energy. That is, thanks to thyroid hormones, we get energy.
If the level of T3 and T4 is too low, a person feels exhausted, may have a loss of strength, weakness. This disease is called hypothyroidism.
If the level of T3 and T4 is too high, all processes in the body are activated. You may feel increased excitability, sleep disorders, even muscle pain. Naturally, weight fluctuations may also occur: a person gains weight, then loses weight. This disease is called hyperthyroidism.
But you need to keep your ears open: symptoms of diseases that arise due to a lack or excess of hormones, doctors may not associate with the thyroid gland at all. Therefore, a thorough diagnosis should be carried out, including hormonal tests.
Interaction of T3 and T4
These hormones must be in a certain ratio, only then does a person feel normal. In order for the T3 hormone to be converted into the T4 hormone, the thyroid gland secretes a special enzyme - TPO. And if this does not happen, then there are obvious disorders in the body.
Another hormone secreted by the thyroid gland is calcitonin. This hormone helps calcium to be processed and absorbed.
Thus, it is possible to prevent a dangerous bone disease - osteoporosis. However, calcitonin does not play any role in increasing excess weight.
Hormones and the Brain
The way the thyroid gland works is directly related to the commands that the brain gives it. There is a section of the brain called the hypothalamus that synthesizes the hormone GST, which activates thyrotropin.
When a woman undergoes hormonal tests, the levels of T3 and T4 hormones, which are concentrated in the blood, can be determined. An excess or deficiency of these hormones signals the brain about how correctly and productively the thyroid gland is working.
This determines whether the brain (or rather, its parts, the hypothalamus and pituitary gland) will produce thyroid hormones.
The hormone GH is produced more when there is a deficiency of T3 and T4. The hormone GRS is produced when there is an excess of them. And vice versa: when the level of GH is low (less than 0.4 units per ml), the doctor may conclude that the thyroid gland is working too actively.
Symptoms of Hypothyroidism (Low Thyroid Hormones)
- Extra pounds that are very difficult to remove
- Weakness, lethargy, energy drain
- Signs of depression: long-term - bad mood, negative thoughts
- Infertility
- Menstrual cycle disorders
- Inability to bear a child
- Body temperature below 36 (the cause may also be a lack of testosterone and estradiol in the body)
- Symptoms of prematurely approaching menopause: hot and cold flashes, mood swings
- Hair loss
- Uneven bowel function, constipation
- Hoarseness of voice
- Rapid heartbeat
- Low blood pressure
- Cold allergy
- Muscle and joint pain
- Slow reactions
- Sensation of "pins and needles" in the palms and wrists
- Deterioration of attention and memory, inability to concentrate even in exceptional cases
- Inability to get enough sleep, interrupted sleep
- Allergies to food, dust, odors
What can hormone tests show?
If your thyroid gland is not functioning properly, your doctor may find the following:
- HSH hormone is higher than normal
- A large number of antibodies produced by the thyroid gland
- Cholesterol is higher than normal
- Liver enzymes are higher than normal
Note: These symptoms can easily be confused with other diseases. Therefore, if you have doubts about the tests, the doctor should prescribe you additional examinations.
Please note that similar symptoms can occur with hypothyroidism or hyperthyroidism. As well as with autoimmune disorders, which can cause abnormal hormone effects.
Thyroid insufficiency syndrome
Hormones affect cell membranes. This is confirmed by scientific research. There are situations when a woman feels symptoms of fatigue, exhaustion, along with excess weight.
The cause may be the effect of hormones on cells. But doctors call this effect abnormal when it causes such symptoms. Moreover, the level of hormones in the body at this time may be absolutely normal.
What is this condition called? Doctors call it thyroid insufficiency syndrome. Scientists have not yet fully studied it and continue to work on research. They believe that this syndrome can affect people who do not even suspect its presence.
Guess what condition of the body accompanies this syndrome? That's right, excess weight.
Diets cause hormonal imbalances and provoke excess weight
Scientists came to this conclusion after studying the impact of diets on hormonal balance and weight fluctuations. In particular, the T3 hormone, which is produced by the thyroid gland, accelerates metabolism and activates cell function more than the T4 hormone.
If its balance is disturbed, it provokes obesity. Therefore, it is very important to maintain a sufficient level of the T3 hormone in the body. Thanks to it, cells produce energy that gives us vitality.
Hormone T3 can be in two forms: bound, passive (then the body takes it from reserves in the blood) and free (in an active, active form). Which hormones T3 to use - bound or free - the body regulates itself.
If there is too little free T3 hormone, the body takes its bound form, and if there is not enough bound T3, many functions of organs and systems are disrupted.
Excess of free T3 hormone is also bad. Then the so-called "thyroid storm" or thyroid storm occurs, when T3 overstimulates the thyroid gland.
This, in turn, affects the cells, which also become very active, and the whole body becomes like a broken clock mechanism, in which the hands spin at a crazy speed, as they please.
Excessive exposure to the T3 hormone can even destroy cells. This means that a person's heart, lungs, nervous system, and other organs and systems may be disrupted.
The worst thing with hyperactivity of the T3 hormone is the heart. The fibers of the heart muscle can be destroyed, which provokes heart disease.
Therefore, when there is an excess of the T3 hormone in the body, a defense mechanism is activated that regulates the level of hormones and their effect on organs.
Protection from T3 hormone
Don't be surprised, such natural protection exists. Its principle is that when there is an excess of T3 hormone, its active form transforms into a bound, inactive one.
How does this happen? In our brain and in other parts of the body there are sensors that are able to catch signals about problems in the body, failures in any system. For example, in the food intake system.
Then, through metabolism, energy reserves are regulated in the body. For example, if there is insufficient energy supply from the cells, the metabolism slows down so that a person has strength. And if the cells are overworked, the metabolism speeds up, then we get even more energy than we should.
When metabolism slows down, a person can gain weight. When it speeds up, they can lose weight. And this is despite strict diets or overeating.
What are the risks for women when they are undernourished?
Let's talk about what happens when a person goes on a strict diet or is undernourished for some other reason. The body produces much less T3 hormone. And the one that is produced remains mostly in a bound (passive) form.
The body detects this with its sensors and, in order to conserve the energy that the cells are now lacking, it slows down its metabolism. In this way, it can survive on a meager diet for some time.
And a paradox occurs: you should lose weight because you eat less and your fat tissue should decrease in volume. But you, on the contrary, gain weight!
The body begins to perceive the state of starvation as threatening and accumulates fat tissue "in reserve". At the same time, calories are burned very slowly, and you do not lose weight, but gain it.
Soy as a salvation from excess weight?
Soy products are now sold in abundance. They are advertised as healthy and weight-loss products. What substances are actually contained in soy and is it really that healthy?
Scientists have named these substances isoflavones. They have the property of converting the thyroid hormone T4 into the hormone T3.
Isoflavone consists of genistein and daidzein, substances that have the property of inhibiting the iodine processing processes in the thyroid gland. This means that the human body develops a deficiency of iodine when there is an excess of soy in the diet.
It has been scientifically proven that a lot of soy in the menu can provoke goiter diseases or weak thyroid function. In particular, it can stop or slow down the production of thyroid hormones, causing hypothyroidism.
In Japan, for example, soy products cause these diseases more often than anywhere else in the world because the Japanese consume a lot of soy.
Soy and the child's body
American studies conducted back in 1950 proved that soy products should not be included in baby food. The enzyme found in soy can disrupt the thyroid gland in children.
These studies were not made publicly available, and soy is still being advertised as a healthy product.
Soy Products for Middle-Aged Women
Reviews of them are not very flattering. According to statistics, women over 40 have thyroid problems 20 times more often than those who are younger. This condition is aggravated by soy products or supplements.
Soy in the diet of women over 40 can increase the risk of developing thyroid disease, aggravate the course of menstruation, and add problems with excess weight.
Clover and millet (the little yellow grains that are also fed to chickens) can have the same harmful effects.
Research conducted in the UK shows that women in the pre-menopausal period who consumed up to 60g of soy once a day for a month very quickly began to complain of irregular periods.
These disturbances continued even after 3 months after the women stopped eating soy products, including drinking soy milk.
Therefore, thyroid hormones play an important role in your well-being and appearance. It is important to know what their balance is in order to control your weight and be able to normalize it in time.