The thyroid: a small organ with a big impact
The thyroid is a butterfly-shaped organ at the front of the neck that produces hormones reaching almost every cell in the body. The most important thyroid hormones are thyroxine (T4) and triiodothyronine (T3). Among other things, they regulate energy expenditure, body temperature, heart rate and the metabolism of fats and carbohydrates.
If the thyroid produces too little of these hormones, this is referred to as an underactive thyroid (hypothyroidism). A common cause in Austria and Central Europe is the autoimmune condition Hashimoto's thyroiditis, in which the immune system attacks the thyroid tissue.
Underactive thyroid and weight: what happens in the body?
Thyroid hormones act like a "pacemaker" for the basal metabolic rate – that is, the amount of energy the body uses at rest. If they are reduced, energy expenditure may fall. This explains why pronounced hypothyroidism can lead to weight gain, even when diet and exercise have barely changed.
Typical signs of hypothyroidism
- Fatigue and reduced performance
- Sensitivity to cold
- Dry skin and brittle hair
- Constipation
- Low mood
- Difficulty concentrating
- Moderate weight gain
Important to know: hypothyroidism rarely explains very substantial weight gain. In the first few weeks, additional body weight is often due to fluid retention rather than solely to an increase in fatty tissue.
Hypothyroidism and metabolism: the mechanisms
The link between hypothyroidism and metabolism can be attributed to several effects:
- Lower basal metabolic rate: Reduced thyroid hormone levels generally mean lower energy expenditure at rest.
- Altered fat and carbohydrate metabolism: The processing of nutrients may be slower, which can affect cholesterol and blood sugar levels.
- Fluid retention: With pronounced underactivity, fluid can accumulate in the tissue (so-called myxoedema).
- Lack of drive and fatigue: Those who feel exhausted often move less – this too can shift the energy balance.
Weight gain in untreated hypothyroidism is usually in the range of a few kilograms. An underactive thyroid is therefore only rarely the sole cause of significant overweight.
The TSH value: a central parameter in diagnosis
The TSH value (thyroid-stimulating hormone) is the most important laboratory parameter for assessing thyroid function. TSH is produced in the pituitary gland and stimulates the thyroid to produce hormones.
- Elevated TSH: Often an indication of an underactive thyroid, as the pituitary attempts to stimulate a "sluggish" thyroid more strongly.
- Low TSH: May indicate an overactive thyroid.
In addition, the free hormones fT3 and fT4 are usually measured and – if Hashimoto's is suspected – antibodies such as TPO-Ab are determined. The precise interpretation belongs in medical hands, as reference ranges can vary depending on the laboratory, age and life situation (e.g. pregnancy).
Subclinical and overt hypothyroidism
Doctors broadly distinguish two forms:
- Subclinical (latent) hypothyroidism: TSH is elevated, while fT3 and fT4 are still normal. Symptoms are often non-specific or absent altogether.
- Overt hypothyroidism: TSH is elevated and fT3 and/or fT4 are reduced. Symptoms are more pronounced.
Whether and when treatment is appropriate depends on the individual findings, any accompanying conditions and the symptom profile.
Treatment: what does it mean for weight?
The standard treatment for hypothyroidism is the administration of the thyroid hormone levothyroxine in tablet form. The aim is to adjust the hormone balance so that values lie within the individually appropriate range.
Many of those affected want to know: do you automatically lose weight when taking thyroid hormones? As a rule, no. Once hormone production is balanced, the metabolism often normalises step by step. Fluid retention can decrease and fatigue frequently eases. Significant weight loss through tablets alone, however, is not to be expected. Thyroid hormones are not a means of losing weight and should only be taken when medically indicated.
What those affected can do themselves
Even though the thyroid helps regulate the metabolism, lifestyle factors remain crucial. The following measures can support well-being:
- Balanced diet: Rich in vegetables, wholegrains, pulses, high-quality fats and sufficient protein.
- Regular exercise: A combination of endurance and strength training can boost energy expenditure.
- Sufficient sleep: Lack of sleep affects hormone balance and appetite regulation.
- Stress management: Chronic stress can have an impact on hormone balance.
- Iodine intake: In Austria, table salt is iodised; targeted self-medication with iodine supplements should only take place after consulting a doctor, particularly in cases of Hashimoto's.
When to seek medical advice
If complaints such as persistent fatigue, unexplained weight gain, sensitivity to cold or low mood continue for longer, a medical assessment is advisable. A simple blood test with measurement of the TSH value already provides important clues in many cases.
Checking thyroid values is also often recommended in the following situations:
- When planning a pregnancy or during pregnancy
- With a family history of thyroid conditions
- In the case of abnormal cholesterol values of unclear cause
- With noticeable changes in neck circumference or difficulty swallowing
Conclusion
The link between an underactive thyroid and weight is real, but often less pronounced than many assume. Hypothyroidism can slow the metabolism and contribute to moderate weight gain, but rarely explains significant overweight on its own. The TSH value is the most important initial indicator for diagnosis. Anyone who suspects they may have an underactive thyroid should have their values checked by a doctor – and not rely solely on self-tests or information from the internet.
This article does not replace medical advice.