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If you are being treated for an underactive thyroid, medically known as hypothyroidism, and are struggling to lose body fat, you are not alone. Of the estimated 4.6 percent in the U.S. who have hypothyroidism, many find themselves with undesirable weight gain.

Even after diagnosis and treatment, it may be extremely difficult to lose weight. You may even find yourself gaining weight, so attaining your personal body composition goals seems impossible.

This article provides information about thyroid function and its role in obesity, discusses the possible barriers to improving body composition even with treatment, and gives you specific steps you can take to lose weight.


The small but mighty thyroid gland

The thyroid gland is a small butterfly-shaped gland located low on the front of your neck. It secretes several hormones, primarily T3 (triiodothyronine) and T4 (thyroxine), that act on every cell throughout the body to regulate metabolism, growth and development, and body temperature.  These hormones also affect breathing, heart and nervous system functions, muscle strength, menstrual cycles, weight and cholesterol levels.

The thyroid functions by receiving information from the hypothalamus and pituitary gland located in the brain.  The pituitary gland, which is like a thermostat for your body, stimulates the thyroid by secreting Thyroid Stimulating Hormone (TSH).  When the pituitary senses a low concentration of thyroid hormone in your blood, it produces more TSH to signal to increase production of T4 or T3.  If thyroid hormone levels are high, the pituitary produces only tiny amounts of TSH.


Thyroid dysfunction

Millions of people in the U.S., mostly women, have thyroid diseases – ranging from a harmless goiter (enlarged gland) to life-threatening cancer.  An abnormal production of thyroid hormones is the most common thyroid condition.

If your thyroid makes too much thyroid hormone, you have hyperthyroidism.  Common symptoms include uncontrolled weight loss, rapid heart rate, and heat sensitivity.

With hypothyroidism, insufficient thyroid hormone is secreted to meet the body’s needs, and body functions slow.

Common causes of underactive thyroid include autoimmune disease, such as Hashimoto’s disease, inflammation (thyroiditis), surgical removal of part or all of the gland, radiation treatments, treatments for hyperthyroidism, and certain medications.

If you have hypothyroidism, you may gain weight, feel tired, have dry hair and skin, be constipated, and have an intolerance to cold.

Hypothyroidism is treated with daily thyroid hormone pills to replace the amount of hormone your body is no longer producing.


The link between hypothyroidism and weight gain

Weight gain or the inability to lose weight is a common concern for people with hypothyroidism.  Even when on treatment, there is usually only a modest loss in weight.

The way the thyroid functions to affect weight and body composition is quite complex. Research has found interactions between thyroid hormones and factors directly affecting energy expenditure, such as fat tissue, other hormones, and the brain.

Although clinicians are not certain whether hypothyroidism causes obesity or vice versa, there is undoubtedly a link between the two.


Barriers to weight loss

It is frustrating to struggle to lose weight or continue to gain weight, even while taking your daily medication. There are five potential barriers that may be making weight loss difficult for you:


  • Suboptimal Thyroid Treatment


Most people with hypothyroidism are treated with thyroid hormone replacement medication to restore TSH levels to what is known as “reference range.”  A reference range is a set of values that includes an upper and lower limit of a lab test that are considered normal for a defined healthy population.

When you fall within the TSH reference range, you are euthyroid, which means your thyroid function is considered clinically “normal”.; however, this may not mean it is optimal for you. Many people experience symptoms while in the “normal” range.

There are a few factors that can affect how well your treatment is working.

The timing of your medication is a key factor, since a number of foods, supplements and drugs interfere with the absorption or action of levothyroxine in the body.

Also, researchers have found that TSH levels in the upper end of the reference range are linked to increased weight and higher rates of obesity.  In fact, even small increases in TSH within the normal range are associated with weight gain.


  • A Decreased Metabolic Set Point


Why is it that that your friend eats more than you do, doesn’t exercise nearly as much, but easily maintains a lower weight?  It may be that you have a lower metabolism than she does.

Metabolism is the process by which your body converts the food you eat into energy.  It is essential to ensuring your body has sufficient energy to function while protecting you from starvation.  Your metabolism works like a thermostat (remember the pituitary?) to maintain your body fat percentage – slowing down or speeding up to maintain a certain set point range.

When your body senses you are in a state of “famine”; for example, if you consistently eat too few calories, it adjusts by decreasing your metabolic set point. Similarly, hypothyroidism leads to chronically slower metabolism, and as you take in more calories than you burn, the body establishes a new, lower metabolic set point.  This means fewer calories are needed to maintain body weight, making weight loss more difficult.


  • Other Thyroid Hormones


The treatment most commonly used for hypothyroidism is synthetic T4 hormone, called levothyroxine; however, T4 is not the only thyroid hormone that affects your metabolism.

Triiodothyronine (T3) works at the cellular level delivering oxygen and energy.  T3 is produced by the thyroid as well as through conversion of T4 to T3.  Lower T3 levels are associated with lowered resting metabolic rates.  A lower metabolism requires less caloric intake and more physical activity to maintain current body weight or to lose fat.  Some people, due to genetics, have an increased need for T3.  These people may benefit from a T4/T3 combination therapy,  such as levothyroxine plus liothyronine (synthetic T3).

Thyroid Binding Globulin (TBG) is a transportation hormone that carries T3 and T4 through your bloodstream to your cells.  If you have too little or too much TBG, your thyroid hormones cannot get to your cells adequately or efficiently.


  • Insulin Resistance


Insulin, another hormone released by your pancreas, increases after you eat sugar or carbohydrates. Insulin stimulates your cells to absorb the excess sugar in the blood, storing it for energy and protecting your body from high glucose levels.

When insulin levels remain chronically elevated, your body becomes resistant to insulin, which means the cells are less responsive, and more insulin is required to maintain normal blood sugar levels. Research has found that people with hypothyroidism are more likely to be insulin resistant.

Elevated levels of insulin not only increase your risk of developing Type 2 diabetes, it causes weight gain, even if you eat fewer calories, by making your cells better at storing fat and increasing cravings for carbohydrate-rich foods.

  • Leptin Resistance

Leptin, a hormone secreted by your fat cells, acts on the hypothalamus in your brain to regulate metabolism and appetite.  As you accumulate more fat cells, leptin levels increase and signal to the brain there is adequate energy storage.  In response, your pituitary gland increases TSH to stimulate thyroid production and your body burns fat rather than storing it.

Leptin resistance occurs much like insulin resistance.  The hypothalamus becomes unresponsive to chronically high levels of leptin, which causes your brain to act as if the body is in a state of starvation.  Metabolism slows, appetite increases and you gain weight, which further increases leptin levels. Recent research has shown that leptin resistance contributes to a reduced metabolic set point.

Not only is leptin resistance linked to obesity, recent studies have discovered a link to hypothyroidism as well.  Leptin resistance makes you chronically hungry and prevents your body from using stored fat, which creates weight gain and can makes weight loss more difficult.


Steps to attaining your ideal body composition

Hope is not lost!  Your motivation may be lagging because the weight is not melting off even while taking thyroid hormone replacement.  There are proactive steps you can take to address issues keeping you from meeting your goals.

Get your thyroid tested – Discuss the results with your doctor to see if your TSH levels are in the higher end of the reference range, or if your T3 or TBG is low.  You may need to adjust your current medication or supplement with T3 in order to find your optimal thyroid levels.

Optimize your thyroid medication – Take levothyroxine on an empty stomach either a half hour before breakfast or before bedtime.  Wait at least three to four hours after taking your medication before taking supplements or drinks that contain calcium or iron.  Also, discuss any changes in your medications with your doctor.

Get tested for insulin and leptin resistance – If you have these conditions, discuss treatment options with your doctor.

Exercise regularly – Lifestyle changes, such as physical activity, which improve body composition (even without a change on the scale), improve thyroid function.  Regular exercise raises your metabolism, curbs your appetite, lowers blood sugar levels, and reduces insulin and leptin resistance.

Change your diet – Work with your doctor to find a diet plan that will provide optimal thyroid health and control your weight while helping to manage or prevent conditions associated with hypothyroidism.

Change your eating patterns – Larger, less frequent (2-3) meals each day with few or no between-meal snacks may be more effective at controlling insulin and leptin levels, which will optimize fat usage.  Avoid excess calorie restriction as that may further lower your metabolic set point.

Get your 8 hours of sleep – Getting enough sleep controls insulin and leptin as well as stress hormone levels.


Jennifer Boidy, RN is a freelance healthcare content writer who is always on the lookout for innovative technologies that improve health and the delivery of healthcare.  Jennifer resides in Manchester, MD with her husband, two teenagers, dog, cat, and plenty of wildlife.

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