Unexplained Weight Gain – Is It Your Thyroid?

The regulation of metabolism and body weight is complex, with many hormones, proteins, and chemicals involved, including hormones produced by the thyroid gland. This small but powerful butterfly-shaped organ in the front of your neck produces thyroid hormones, which influence a number of vital functions such as growth and development, metabolism, and body temperature. As a result, thyroid disorders including hypothyroidism and hyperthyroidism can cause a wide range of symptoms, among them changes in body weight. But don’t assume a problem with your thyroid is causing your weight gain. Read on for a better understanding of the relationship between your thyroid and weight gain, as well as what to do about it. 

Hypothyroidism and Weight Gain

Hypothyroidism is a fairly common condition in which an underactive thyroid gland produces insufficient amounts of thyroid hormones. Hypothyroidism can be caused by autoimmune conditions, surgical removal of all or part of the thyroid gland, radiation therapy, and certain medications. Symptoms of hypothyroidism include fatigue, constipation, menstrual irregularities, and depressed mood. Because of the role of thyroid hormones in metabolism, hypothyroidism can lead to weight changes as well, specifically weight gain. But the amount of weight gain associated with hypothyroidism is typically mild to moderate, 5-10 pounds on average, and typically seen in people with severe hypothyroidism who therefore exhibit other symptoms as well. If you’ve experienced significant weight gain, especially if you otherwise feel well, it is more likely related to a combination of factors such as your genetics, nutrition, physical activity, or other medications, not your thyroid. 

Why Does Hypothyroidism Cause Weight Gain?

Of course it may be reasonable to consider hypothyroidism if you’ve gained weight without apparent reason and are experiencing other symptoms of thyroid disease. After all, hypothyroidism is associated with reduced energy expenditure, which is how many calories the body is burning at rest. With reduced energy expenditure comes an increased likelihood of eating more calories than you’re burning, which can lead to weight gain. But hypothyroidism also comes with a decrease in appetite, so affected people are also likely to be eating less, which is why their weight may not change much. 

Will taking thyroid hormone help me lose weight? 

Taking thyroid hormone has not been proven to help with weight loss unless you have hypothyroidism diagnosed by abnormal blood tests. For those with confirmed hypothyroidism, taking thyroid hormone is necessary and can help to improve symptoms, but research suggests that the weight change occurring after starting thyroid hormone is small and typically secondary to changes in water retention. So while treating hypothyroidism is very important for your overall health, it may not be the magic bullet for weight loss that you were hoping for. 

Additionally, there are risks associated with taking thyroid hormone when your body produces enough, or with taking more than what is needed to restore normal blood levels. 

Hyperthyroidism and Weight Gain

Hyperthyroidism is a less common condition characterized by elevated levels of thyroid hormones. When thyroid hormone levels are elevated, symptoms can include nervousness, irritability, increased heart rate, increased sweating, difficulty sleeping, and muscle weakness. Causes of hyperthyroidism include an autoimmune condition called Grave’s Disease (the most common cause), toxic nodular or multinodular goiter, and thyroiditis. You can also develop hyperthyroidism if you are taking too much thyroid hormone. Because of the association between thyroid hormones and metabolism, weight changes can occur with hyperthyroidism as well. This is typically weight loss which can occur despite an increase in appetite usually associated with hyperthyroidism. 

Can Hyperthyroidism Cause Weight Gain?  

While less common, weight gain can also happen in hyperthyroidism. Reasons for this include the following: 

  • Increased appetite – A common symptom of hyperthyroidism, increased appetite can lead to increased eating, which can cause weight gain. The associated increase in resting metabolic rate that occurs with elevated thyroid hormone levels usually offsets this, but sometimes weight does increase. 
  • Treatment – The most common reason for weight gain with hyperthyroidism is that once treatment has caused thyroid hormone levels to return to normal, weight will typically return to what it had been before the hyperthyroidism developed. Sometimes even more weight is gained after treatment as a person may continue to eat more calories as they had been doing when they were in a hyperthyroid state. 

Another consideration is the use of a class of medication called beta blockers to treat  the symptoms of hyperthyroidism. Some beta blockers have been associated with weight gain, so it’s possible that using these medications to treat hyperthyroidism could be the reason for some weight gain with treatment. 

If you’ve been diagnosed with a thyroid disorder and are gaining weight or having difficulty losing weight, the first thing to do is to make sure your thyroid condition is being appropriately treated. Check in with your healthcare provider to see if a blood test to check your thyroid hormone levels is warranted. For most people, this is a reliable way to determine if your thyroid treatment is adequate. 

Once thyroid disease is properly treated, there should not continue to be a significant impact on weight. Implementing a healthful, low-calorie diet and increasing physical activity are the next steps to managing thyroid-related weight gain. And don’t forget about stress and sleep! We often focus so much on food and physical activity that we forget about the importance of stress management and adequate sleep for losing and maintaining weight.  

If you’ve been doing these things and have not been successful, it may be time to consider seeking professional assistance, such as that of a Registered Dietitian and/or an Obesity Medicine Physician. These providers can use evidence-based tools, including prescription weight loss medication if appropriate, aimed at addressing biological factors that may be interfering with your success.

If you’re looking for a sustainable, realistic, and personalized program that fits your lifestyle, Form Health may be right for you. By using physical activity, mindset shifts, nutrition and FDA-approved medication, if appropriate, your clinical team  will help you achieve your weight loss goals. 

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About the Author: Brooke Marsico, PA-C, completed her physician assistant training at Midwestern University in 2011. She began her practice in the field of Obesity Medicine at Northwestern Memorial Hospital in Chicago where she practiced from 2016 to 2021. She went on to treat patients living with obesity at Cleveland Clinic from 2021 to 2022 prior to joining the team at Form Health. Brooke is passionate about helping patients living with obesity achieve meaningful weight loss and improve their health. Her practice focuses on individualized behavioral and pharmacological intervention to help patients reach their goals. She is also experienced in managing patients who have a history of bariatric surgery.

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