Influence of the thyroid gland on digestion — why diets do not help with hypothyroidism
The thyroid gland — small and inconspicuous, but with a far underestimated influence on our entire body. The butterfly-shaped organ produces hormones that act like the “gas pedal” of our metabolism. If there are too many hormones, the body and soul run “overdrive”; if there are too few, they run “underdrive” and slow down. Diseases of the thyroid gland are extremely common and can occur at any age. Since thyroid disorders develop very unspecifically and insidiously, they often remain undetected and untreated for a long time. In about one in three adults in Germany, at least one pathological thyroid change develops in the course of a lifetime — with increasing frequency in old age.
Function and task of the thyroid gland
As a hormone gland, the thyroid gland performs an important control function in the human body. Hormones are important messenger substances that can influence and regulate other organs.
The term thyroid hormones covers the two most important hormones thyroxine (T4) and triiodothyronine (T3). The numbers 3 and 4 represent the number of iodine atoms contained in the hormones. Thyroxine has four iodine atoms (T4), while triiodothyronine has only three (T3). By splitting off one iodine atom, the body can form the shorter-lived but more potent hormone T3 from the less effective T4.
Both hormones — T3 and T4 — have an effect on the heart and circulation, dilate the blood vessels, accelerate the heartbeat and regulate blood pressure. But they also activate fat and connective tissue metabolism, sweat and sebaceous gland production in the skin, and kidney and intestinal activity. In addition, thyroid hormones are essentially responsible for many growth processes and increase the basal metabolic rate and energy consumption of the entire organism. Thyroid hormones act primarily on:
- Heart activity and blood pressure
- energy metabolism, body weight
- Carbohydrate metabolism, insulin production
- Fat and protein metabolism, cholesterol levels
- Brain activity, psyche
- Muscle metabolism, muscle strength
- Intestinal activity, digestion
- Growth and maturation of unborn children in the womb and of children
How does the thyroid gland know how much hormone to produce?
The thyroid gland is involved in a complicated hormonal control loop that normally keeps hormone secretion in balance and adjusts it to daily requirements.
A healthy thyroid gland produces about 80 to 100 micrograms of T4 and 10 to 50 micrograms of T3 per day. When and in what quantity the thyroid gland makes the stored hormones available to the body is controlled by the brain. From there, the concentration of thyroid hormones in the blood can be measured and the thyroid gland’s production can be cranked up or slowed down accordingly. Through this normally well-functioning control circuit, the hormone level can be adjusted to the current need. A proper level of thyroid hormone in the blood is called euthyroidism, a level that is too high is called hyperthyroidism (overactive thyroid), and a level that is too low is called hypothyroidism (underactive thyroid).
How does the thyroid gland affect metabolism?
Thyroid hormones regulate the entire metabolism — and thus also the basal metabolic rate of the cells. They promote the generation of heat in response to cold, stimulate carbohydrate utilization and fat metabolism. In the case of a deficiency — i.e. hypothyroidism — all metabolic processes are slowed down, the basal metabolic rate in the cells and thus also the energy requirement are reduced. This not only affects performance, the cardiovascular system, the gastrointestinal tract, the nervous system and fertility, but also weight. If the basal metabolic rate is suddenly reduced, body weight increases even though nothing changes in eating habits. The body requires less energy than when thyroid hormone levels are normal. This weight gain is mainly due to water retention and is not related to an increase in fat mass. In addition, there is slower digestion with often chronic constipation and increasing feelings of hunger. About 1 to 2 out of 200 people are affected by hypothyroidism, women more often than men.
Conversely, severe hyperthyroidism often results in weight loss due to increased energy consumption; an effect that can in principle also be used for desired weight loss, for example by including synthetic thyroid hormone in illegal weight-loss pills and thus inducing artificial hyperthyroidism. However, due to the associated risks on the part of the cardiovascular or nervous system, weight loss with the help of thyroid hormones is strictly not recommended.
How do I recognize hypothyroidism?
The symptoms of hypothyroidism are very non-specific and in many cases are misinterpreted or overlooked. Fatigue, muscle weakness, thinning hair, unclear weight gain and dry skin are typical signs.
Why is iodine so important?
No iodine, no thyroid hormone. Iodine is the basic substance for the production of thyroid hormones. Since the human body cannot produce iodine itself and can only store it to a very limited extent, iodine is one of the essential trace elements and must be taken in regularly with food. It enters the blood via the gastrointestinal tract and from there actively enters the thyroid gland. In the thyroid gland, up to 80 percent of the iodine ingested daily is consumed.
Where is our daily iodine requirement?
To be able to form sufficient thyroid hormones, the daily iodine requirement for adults is about 150 to 200 micrograms. The German Nutrition Society has formulated specific recommendations for iodine intake depending on a person’s age and gender. The daily iodine requirement is about 200 micrograms. With a daily consumption of 5 g of table salt, iodized table salt provides 75–125 µg of iodine. Fish, algae, dairy and soy products in particular are among the foods richest in iodine (for a list, see chart, p. 12 https://schilddrueseninstitut.at/Jodbroschuere.pdf ).
What are the risks of iodine deficiency?
Germany is one of the regions in Europe with the lowest iodine deficiency. Thousands of years ago, glacial melt washed away the trace element. To this day, iodine is found only in very small quantities in our soils, croplands and pastures, and in drinking water, and is thus largely absent from animal and human food. It is true that the supply of iodine to the population has improved greatly in recent decades. Iodine intake has almost doubled since 1975, and newborns and children in particular now have a balanced iodine budget. However, experts believe that at least one third if not half of the German population is still not optimally supplied with iodine. The daily deficit is estimated at one third of the amount of iodine recommended by the German Nutrition Society (DGE).
How much weight can I expect to lose if the hypofunction is treated?
Since much of the weight gain in hypothyroidism is due to the accumulation of salt and water, you can expect to lose a small amount of weight (usually less than 10% of your body weight) when you are treated for hypothyroidism. Treatment with thyroid hormones should be expected to result in a return to the original body weight. However, because hypothyroidism usually develops over a long period of time, it is quite common to not see significant weight loss after successful treatment of hypothyroidism. Again, if all other symptoms of hypothyroidism, with the exception of weight gain, have resolved with thyroid hormone treatment, it is less likely that the weight gain will be due solely to the thyroid. Once hypothyroidism is treated and thyroid hormone levels return to normal, the ability to gain or lose weight is the same as in people who do not have thyroid problems.
Can thyroid hormones be used for weight loss?
Thyroid hormones have been used in the past as a weight loss tool. Many studies have shown that treatment with excess thyroid hormones can result in greater weight loss than can be achieved through diet alone. However, once the excess thyroid hormone is discontinued, the excess weight loss is usually regained. In addition, taking thyroid hormones to support weight loss can have significant negative consequences, such as loss of muscle protein in addition to any loss of body fat. Increasing thyroid hormone dose is unlikely to result in significant weight change and may lead to other metabolic problems.
Text Sources:
(1) Ríos-Prego, M., Anibarro, L., & Sánchez-Sobrino, P. (2019). Relationship between thyroid dysfunction and body weight: a not so evident paradigm. International journal of general medicine, 12, 299–304. https://doi.org/10.2147/IJGM.S206983
(2) https://www.btf-thyroid.org/thyroid-and-weight-the-science
(3) https://www.deutsches-schilddruesenzentrum.de/wissenswertes/
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