Hormones and weight: testosterone, FSH, thyroid

Testosterone, follicle-stimulating hormone (FSH), and thyroid hormones belong to different systems, but are often considered together when evaluating patients with weight, menstrual cycle, fertility, libido, chronic fatigue, and mood swings. These hormones regulate sexual function, metabolism, muscle and bone function, energy, and overall well-being, so testing them can help identify underlying endocrine causes of complaints. [1]

Current guidelines emphasize that hormone tests should not be ordered "just in case." Doctors rely on specific symptoms: decreased libido, erectile dysfunction, infertility, menstrual irregularities, signs of hypo- or hyperthyroidism, unexplained weight gain or loss, and hair and skin changes. For such complaints, testing testosterone, FSH, and thyroid hormones helps distinguish "normal" lifestyle effects from true endocrine disorders requiring specific treatment. [2]

Testosterone is primarily important for assessing hypogonadism in men and androgen excess in women. FSH helps understand the function of the testes or ovaries, as well as the pituitary gland, which controls the gonads. Thyroid-stimulating hormone (TSH), free thyroxine (free T4), and sometimes triiodothyronine (T3) are used to diagnose thyroid disorders, which are directly related to energy levels, thermoregulation, and body weight. [3]

Not everyone needs endocrine testing if they are obese or have difficulty losing weight. However, if excess weight is accompanied by severe weakness, drowsiness, intolerance to cold or heat, sudden changes in the menstrual cycle, decreased potency, or hair loss, the doctor often includes hormonal testing in the basic examination. This helps identify hypothyroidism, hyperprolactinemia, hypogonadism, or other disorders that, if left untreated, can interfere with weight loss and worsen the prognosis. [4]

It's important to remember that interpretation of hormonal tests should always take into account age, gender, cycle phase, medication use, and the overall clinical picture. The same testosterone or TSH value may be normal for one person and abnormal for another. Therefore, relying solely on the "asterisks" on the form without consulting a doctor is inappropriate. [5]

Table 1. Main objectives of hormonal tests

Analysis	What does it answer?
Total/free testosterone	Is there a deficiency or excess of androgens?
FSH	How the testicles/ovaries and pituitary gland work
TSH, free T4 (sometimes T3)	Is thyroid function normal?
Additional hormones (as indicated)	Clarification of the causes of cycle disorders, fertility, weight

Testosterone: When it makes sense to test and how to interpret the results

Testosterone is the major androgen hormone in men and an important hormone in women at low concentrations. It influences libido, erectile function, muscle mass and strength, bone density, fat distribution, mood, and energy levels. Testosterone testing is prescribed for suspected hypogonadism in men and for signs of androgen excess in women. [6]

In men, indications for testing include decreased libido, erectile dysfunction, infertility, decreased or absent facial and body hair, decreased muscle mass and strength, unexplained osteoporosis, and unexplained anemia. Recommendations emphasize that testosterone should not be measured solely due to age or mild fatigue, without characteristic deficiency symptoms. [7]

In women, testosterone is typically tested when androgen excess is suspected: increased male-pattern hair growth (hirsutism), male-pattern hair loss, acne, menstrual irregularities, suspected polycystic ovary syndrome, or androgen-secreting tumors. For women, not only total testosterone concentrations but also free (bioavailable) testosterone levels are clinically important, especially when plasma proteins are altered. [8]

Blood tests for testosterone are usually recommended to be taken in the morning, on an empty stomach, when hormone levels in men are at their highest. If results are questionable or borderline, the test is repeated, often twice, to rule out random fluctuations. If a decrease or excess of testosterone is detected, the doctor will additionally prescribe FSH, luteinizing hormone (LH), prolactin, and sometimes endocrine gland tests to determine the cause. [9]

It's important to remember that testosterone therapy is not indicated for everyone and has clear indications. In men, it is used for confirmed hypogonadism with low testosterone and characteristic symptoms. In women, the proven indication is severely reduced sexual desire in postmenopausal women after excluding other causes; however, the dosages are significantly lower than those for men. Self-medication with testosterone without proper diagnosis can lead to serious side effects and suppression of the body's hormonal system. [10]

Table 2. When a doctor typically orders a testosterone test

Patient	Main indications for the test
Man	Decreased libido, erectile dysfunction, infertility, hair loss, muscle loss, osteoporosis
Woman	Hirsutism, acne, alopecia, menstrual irregularities, suspected polycystic ovary syndrome
Teenager	Delayed or premature puberty
Any gender	Suspected androgen-secreting tumors

FSH in women: ovarian reserve, cycle, and menopause

Follicle-stimulating hormone (FSH) is produced by the pituitary gland and stimulates the ovaries in women and the testes in men. In women, FSH regulates follicle maturation and estrogen production. Its levels fluctuate throughout the cycle and life: they increase during peri- and postmenopause, when ovarian reserve declines. FSH testing helps assess ovarian function, the causes of menstrual irregularities, and fertility. [11]

In women of reproductive age, FSH is most often measured in cases of irregular menstruation, anovulation, infertility, suspected polycystic ovary syndrome, premature ovarian failure, or when assessing ovarian reserve before assisted reproductive technology programs. Elevated FSH may indicate a decrease in the quantity and quality of eggs, while low FSH may indicate problems with the pituitary gland or hypothalamus. [12]

During the transition to menopause, FSH levels gradually increase as the ovaries become less responsive to stimulation, and the pituitary gland "turns up the volume" of the signal. High FSH levels, along with irregular or absent periods and hot flashes, often indicate menopause or perimenopause. However, laboratory guidelines themselves emphasize that the diagnosis of menopause in women over a certain age is based primarily on clinical findings, not a single FSH level. [13]

When interpreting FSH, it's important to consider the day of the cycle. The test is typically scheduled for days 2-3 of the cycle, when baseline hormone levels and the state of ovarian reserve can be more objectively assessed. Values and reference ranges depend on the cycle phase, age, and laboratory method, so conclusions are made only based on the specific form and accompanying data (estradiol, anti-Müllerian hormone, ovarian ultrasound). [14]

FSH is not a standalone "fertility test" or "menopause test." It is an important piece of a puzzle that includes age, clinical symptoms, other hormones, and ultrasound data. Neither a low nor a high FSH level eliminates the possibility of becoming pregnant without discussing a specialist strategy with a doctor, especially given modern reproductive medicine technologies. [15]

Table 3. Main situations when women have their FSH checked

Situation	The task of analysis
Irregular cycle, anovulation	Evaluation of ovarian and pituitary function
Infertility	Clarification of ovarian reserve and causes
Suspected early menopause	Confirmation of decreased ovarian function
Preparation for IVF and other programs	Assessing the chances of response to stimulation
Suspected polycystic ovary syndrome or other disorders	Differential diagnosis

FSH in men: spermatogenesis and testicular function

In men, FSH acts on the Sertoli cells in the testes and stimulates sperm production. FSH testing is prescribed for decreased fertility, suspected spermatogenesis disorders, and signs of hypogonadism, when it is necessary to distinguish between primary (testicular) and secondary (pituitary-hypothalamic) forms. [16]

If a man has decreased sperm count or quality, FSH can help identify where exactly the system is "broken." Elevated FSH with low testosterone and impaired spermatogenesis indicates primary testicular damage: the pituitary gland is trying to stimulate them more intensely, but the tissues are responding poorly. Low or normal FSH with low testosterone and impaired fertility may indicate secondary hypogonadism, when the problem lies in the pituitary gland or hypothalamus. [17]

In addition to fertility, FSH levels in men are assessed for delayed or early puberty, suspected Klinefelter syndrome, and other genetic syndromes. In adolescents, abnormal FSH and luteinizing hormone levels help differentiate between constitutional developmental characteristics and pathological conditions. [18]

Preparation for the test is usually standard: in the morning, on an empty stomach, without strenuous exercise or alcohol the day before. Since hormones change, if the results are questionable or borderline, the doctor may recommend a repeat test, as well as supplement it with a spermogram, testosterone levels, luteinizing hormone, prolactin, and sometimes karyotyping. [19]

If significant deviations in FSH are detected in men, further steps depend on the objectives: when planning a pregnancy - consultation with a reproductive specialist, if a genetic syndrome is suspected - medical genetic counseling, in case of hypogonadism - discussion of testosterone replacement therapy taking into account the risks and monitoring. [20]

Table 4. Interpretation of FSH in men (simplified)

FSH	Testosterone	Possible interpretation
High	Low / low-normal	Primary hypogonadism, testicular damage
Low/Normal	Short	Secondary hypogonadism (pituitary/hypothalamic)
High	Normal, but spermogram is abnormal	Damage to spermatogenesis
Norm	Norm	There is no evidence of an endocrine cause based on FSH.

Thyroid hormones: TSH, T4, T3 and their relationship with weight

The thyroid gland produces the hormones thyroxine (T4) and triiodothyronine (T3), which regulate metabolic rate, heart function, body temperature, nervous system, and body weight. These hormones are controlled by thyroid-stimulating hormone (TSH), which is produced by the pituitary gland. The primary test for assessing thyroid function is the TSH test; if abnormal, free T4 and sometimes free T3 are usually added. [21]

Hypothyroidism (insufficient thyroid hormone production) can cause fatigue, drowsiness, weight gain, a feeling of coldness, dry skin, hair loss, constipation, slow thinking, and low mood. Tests typically reveal elevated TSH and decreased free T4. Hyperthyroidism (overproduction of thyroid hormones) can cause the opposite symptoms: weight loss, palpitations, sweating, tremors, and anxiety. In this case, TSH is decreased, while T4 and T3 are increased. [22]

Thyroid function is often tested in people with unexplained weight gain, especially if there are accompanying signs of hypothyroidism. However, guidelines emphasize that moderate obesity in the absence of other symptoms does not necessarily indicate hypothyroidism. A TSH test is advisable if weight is accompanied by fatigue, chills, dry skin, menstrual irregularities, infertility, depression, and also if there is a family history of thyroid disease. [23]

Additionally, thyroid peroxidase and thyroglobulin antibodies may be measured if the physician suspects autoimmune thyroiditis. These tests help clarify the cause of hypothyroidism or subclinical disorders, but are not used for routine "screening," as they alone do not determine treatment management in the absence of changes in TSH and T4. Hypothyroidism therapy is typically monitored based on TSH (and sometimes T4), rather than antibodies. [24]

An important practical detail: any thyroid hormone results must be compared with medications (e.g., levothyroxine, amiodarone, glucocorticoids, biotin), concomitant diseases, and difficult-to-interpret borderline conditions (subclinical hypo- and hyperthyroidism). The decision regarding treatment, observation, or further testing should be made by a physician, not just a "color marker" on a form. [25]

Table 5. Simplified interpretation of TSH and free T4

TSH	Free T4	What could this mean?
Increased	Demoted	Overt hypothyroidism
Increased	Norm	Subclinical hypothyroidism
Demoted	Increased	Overt hyperthyroidism/thyrotoxicosis
Demoted	Norm	Possible subclinical hyperthyroidism or drug influence
Norm	Norm	Thyroid function is within normal limits

How to properly prepare for hormonal tests

Preparation for hormonal testing significantly impacts the accuracy of the results. General recommendations include donating blood in the morning, on an empty stomach, or after 8-12 hours without food (water is permitted). It is advisable to avoid intense physical activity, alcohol consumption, and significant stress the day before. It is helpful to sit quietly for 10-15 minutes before the test to prevent anxiety or stress from distorting the results. [26]

For testosterone in men, morning time (usually before 10 a.m.) is important, as hormone concentrations are at their highest and best reflect true levels. For repeated measurements, it's advisable to collect blood at the same time and under similar conditions. Women are sometimes advised to consider the day of their cycle, especially if other sex hormones are being tested simultaneously. All these details should be specified by a physician or laboratory. [27]

In women, FSH is typically measured on days 2-3 of the cycle, when baseline levels are most informative for assessing ovarian reserve. If the cycle is absent or highly irregular, the doctor determines the test date individually. For men, there is no strict time limit, but morning testing under standard conditions (fasting, no exercise or alcohol the day before) is also preferable. [28]

For thyroid tests (TSH, T4, T3), basic preparation is usually limited to a morning fasting blood draw. If the patient is taking levothyroxine, it is most often recommended to draw blood before the morning dose, but the exact schedule depends on the physician's instructions. It is important to inform the laboratory and physician about the use of biotin and other supplements that may interfere with immunological methods for measuring hormones. [29]

Stopping medications without authorization before tests can be dangerous. Adjusting the dosage of hormonal medications, antidepressants, glucocorticoids, antiarrhythmics, and other medications should be discussed with a doctor. Preparation guidelines increasingly emphasize that it is more important to inform the specialist about all medications and supplements in advance than to conceal information out of fear of "impairing the test results." [30]

Table 6. Preparation for hormonal tests: a quick reminder

Analysis	Key rules of preparation
Testosterone	Morning, on an empty stomach, without heavy exercise or alcohol
FSH (women)	2-3 day of the cycle (if any), morning, on an empty stomach
FSH (men)	Morning, on an empty stomach, standard conditions
TSH, free T4	Morning, on an empty stomach, report taking levothyroxine and supplements
All hormones	Do not change medications without consulting your doctor.

When is it really necessary to check these hormones if you are overweight and tired?

When you're overweight, tired, and feeling unwell, it's tempting to "get all your hormones checked just in case." However, clinical guidelines recommend a more targeted approach. Testosterone testing in men is warranted if excess weight is combined with erectile dysfunction, decreased libido, hair loss, muscle loss, osteoporosis, or significant anemia without cause. In women, testosterone testing is indicated for signs of androgen excess and menstrual irregularities. [31]

FSH testing is useful if excess weight is accompanied by reproductive dysfunction: infertility, persistent anovulation, early or late menstrual irregularities, suspected early menopause in women, or impaired spermatogenesis and sexual function in men. In the absence of such symptoms, routine FSH measurement in obese individuals is generally not necessary. [32]

Thyroid tests (TSH and free T4) are often included in the basic evaluation for overweight individuals, as hypothyroidism is relatively common and can cause typical symptoms: chills, dry skin, constipation, puffiness, voice changes, and menstrual irregularities. However, the presence of symptoms and risk factors is also important: family history, autoimmune diseases, thyroid surgery, and neck radiation. Without these indicators, mass screening of all overweight individuals is not always justified. [33]

Normal hormonal test results don't mean your weight and well-being are "not related to hormones at all." Insulin, leptin, and other metabolic signaling molecules are almost never measured routinely, but they actively respond to diet, activity, sleep, and stress. Normal testosterone, FSH, and TSH levels simply indicate that there are no obvious, major endocrine imbalances, and that lifestyle changes are truly meaningful and won't be tilting at windmills. [34]

If the results show significant deviations, further treatment should be determined in consultation with a doctor: sometimes dynamic observation and lifestyle modifications are sufficient, while other times specific treatment is required – from thyroid hormones to testosterone replacement therapy or hormonal support for reproductive function. The key is to avoid prescribing medications based on a single test result and to avoid ignoring symptoms, hoping that "it's just age." [35]