I’m Gaining Weight: Is It My Thyroid?

Published May 2019

A Look at Hypothyroidism

It’s a small gland – but it makes a major impact on your body. See how an underactive thyroid can be one reason why you’re gaining weight.

The Link Between Thyroid and Your Weight

The thyroid gland is a butterfly-shaped gland located in the front of your neck. This gland is responsible for producing, storing and secreting thyroid hormone, an essential hormone for the function of virtually all parts of your body. Reduced production of thyroid hormone can be temporary, but when it is permanent, the result is called hypothyroidism.

Approximately 4.6 percent of people in the U.S. ages 12 and older have some degree of hypothyroidism, the vast majority falling into what is known as “subclinical” or mild hypothyroidism. Mild hypothyroidism is typically asymptomatic but can progress to overt hypothyroidism. “Hypothyroidism from any cause results in a decrease in energy metabolism, or the basal metabolic rate. Patients often experience a modest amount of weight gain prior to diagnosis because of this metabolic slowing,” explains Northwestern Medicine Endocrinologist Eve D. Bloomgarden, MD. Other symptoms depend on the severity of hypothyroidism but commonly include fatigue, constipation, muscle aches and feeling cold. And while this can lead to weight gain for some – that is only a small part of the big picture.

It’s such a common disorder, and I see a lot of misinformation about it, which can be very harmful.

— Eve D. Bloomgarden, MD

Dr. Bloomgarden cautions that the vast majority of weight gain is not thyroid-related, as the thyroid is only one small contributor to the regulation of body weight. “Weight is influenced by many contributors, and unfortunately it’s never as simple as ‘just the thyroid’,” she says. “Importantly, once the hypothyroidism is treated with thyroid hormone, the basal metabolic rate returns to normal, and the weight also returns to normal. If it does not, I work with my patients to address other causes of weight gain, in particular focusing on getting adequate sleep, making healthy food choices and exercising.”

Getting the Right Diagnosis

Hypothyroidism is more likely to develop in women, and a personal history or family history of thyroid issues can increase your risk. To accurately test for hypothyroidism, a blood test for thyroid stimulating hormone (TSH) is used. Even small changes in your thyroid hormone levels (T4 and T3) will cause very big changes in TSH secretion. “The TSH test is really accurate and is the appropriate test for 99 percent of cases. Other lab tests for thyroid function are supplemental, and may not be clinically relevant or appropriate,” adds Dr. Bloomgarden.

Once a diagnosis is confirmed, your physician will work with you to find the appropriate treatment. The most frequently used treatment for hypothyroidism is replacing the hormone with a substitute, known as levothyroxine (LT4). This is a precursor to the active hormone and seeks to replicate the hormones your body is failing to produce properly. “Your body does not care if you make or take thyroid hormone,” adds Dr Bloomgarden.

Causes of hypothyroidism can include:

Hashimoto’s thyroiditis. The most common cause of hypothyroidism, this is an autoimmune disorder that damages your thyroid function. Your body’s white blood cells and antibodies attack the thyroid gland. This leads to chronic inflammation, rendering the gland impaired.
Thyroid removal. Certain conditions may require surgery to remove all or part of the thyroid gland.
Radiation therapy. During radiation therapy for head and neck cancers, the beams may damage the thyroid gland and surrounding tissues. As a result, several types of thyroid problems may develop, including hypothyroidism.

Symptoms of an underactive thyroid can be nonspecific or reflect other issues. You may experience:

Fatigue
Muscle weakness
Thinning hair
Weight gain
Dry skin

Managing Thyroid Issues

There are plenty of other reasons why your thyroid can be easily misunderstood. “It’s such a common disorder, and I see a lot of misinformation about it, which can be very harmful,” says Dr. Bloomgarden. She suggests speaking with your physician to create a personalized plan that meets your own unique needs. She also recommends against taking any supplements or following any fad diets for your thyroid, as these are not backed up by science and have the potential for harm.

If you are gaining weight and experiencing additional symptoms, Dr. Bloomgarden suggests speaking with your primary care physician to see if a TSH blood test is appropriate. While weight gain may not always be explained by your thyroid, this test will help you eliminate it as the cause or, alternatively, start appropriate treatment to manage hypothyroidism.

If you have a thyroid disorder, it should be treated using evidence-based guidelines and prescription medication, says Dr. Bloomgarden. “I want my patients to feel well and not let thyroid disease define them. A lot of people feel terrible, and as soon as we get them on a monitored medication, they feel much better, and they are no longer victim to a swinging metabolism.”

Additionally you can modify lifestyle factors by reducing stress, incorporating physical activity into your routine and adopting a healthy diet.