Many people attribute weight gain to lack of physical activity, a less disciplined diet, or stress and pressure. But what happens when the number on the scale goes up — despite mindful eating, daily movement, and even efforts to lose weight? In such cases, the cause may not be behavioral at all, but medical.
One of the most common and less talked-about reasons for gradual and unexplained weight gain is hypothyroidism — a condition in which the thyroid gland does not produce enough hormones that are essential for regulating the body’s metabolism.
According to doctors, the thyroid gland affects almost every system in the body: Calorie-burning rate, energy levels, the digestive system, fluid balance, and even mood. When its activity slows down — the entire body slows down as well.
Why does hypothyroidism cause weight gain?
The thyroid gland secretes hormones responsible for metabolic rate. When hormone levels are low, the body burns less energy at rest, tends to store fat and fluids — and weight gradually increases.
The weight gain is not always dramatic or rapid. Sometimes it involves a few kilograms that accumulate slowly but hardly respond to diet or physical activity. This is one of the first and most frustrating signs of hypothyroidism.
How can you tell if weight gain is related to the thyroid?
The difficulty in identifying the condition lies in the fact that symptoms are often subtle, develop slowly, and overlap with other common conditions — such as fatigue, stress, or hormonal changes. That’s why it’s important to pay attention to a combination of several signs together.
5 signs that may indicate hypothyroidism:
1. Weight gain without changes in lifestyle habits
This is the main red flag. When weight increases despite no significant change in diet or activity — and sometimes there is even real difficulty losing weight — it may be metabolism that has been affected. Fat tends to accumulate mainly in the abdominal area, and fluid retention may also occur.
2. Persistent fatigue and decreased energy
Fatigue is a very common complaint, so it’s easy to attribute it to stress or lack of sleep. But when it is deep, daily fatigue that does not improve with rest — it may be a hormonal sign. Thyroid hormones are essential for energy production in cells, and when they are lacking, the body operates “in low gear.” The decrease in energy also leads to less movement — creating a cycle that promotes weight gain.
3. Changes in the skin, hair, and nails
The thyroid gland also affects external tissues. Dry, rough, and cold skin, increased hair loss, thin or brittle hair, and slow nail growth — all of these can be signs that the gland is not functioning properly. This is not just an aesthetic issue, but a signal that the body’s systems are slowing down.
4. Hormonal disturbances and changes in the menstrual cycle
In women, hypothyroidism may affect the menstrual cycle — causing irregularity, heavier bleeding, or pain. Hormonal imbalance can also lead to fluid retention and weight gain. Not infrequently, women discover the problem during evaluation for gynecological complaints or fertility difficulties.
5. Neck swelling, digestive problems, and changes around the eyes
In some cases, swelling in the neck area can be noticed — resulting from enlargement of the thyroid gland. In addition, slowed digestive activity causes constipation, bloating, and a “heavy” abdomen, which contributes to a feeling of weight gain. Some people also report swelling around the eyes or slightly blurred vision.
Why is this happening more today than in the past?
Doctors note that in recent years there has been an increase in the diagnosis of mild or subclinical hypothyroidism. Possible reasons include dietary changes, reduced use of iodized salt, chronic stress, and genetic predisposition.
In Israel, where awareness of iodine in the diet is not particularly high, this is a factor worth paying attention to — especially among women.
What should you do if you suspect a problem?
The first step is not to ignore it. A simple blood test can diagnose thyroid function (TSH, and sometimes also T4 and T3). A family physician or endocrinologist can interpret the results and decide whether treatment is necessary.
When hypothyroidism is diagnosed, treatment is usually simple and effective: administering a replacement hormone at a personalized dose. For many people, hormonal balance leads to improvement in energy, digestion, and sometimes also gradual weight loss.
The bottom line: Weight gain is not always the result of a “lack of discipline.” Sometimes it is a sign that something deeper is happening in the body. Listening to symptoms, early identification, and seeking testing can make a significant difference — not only in weight, but in overall health and quality of life.