Managing hypothyroidism or obesity can be challenging — and having both at the same time can be even more complicated. Hypothyroidism (an underactive thyroid gland) has long been linked to obesity, but researchers now think the connection may be more complex than once believed.

Some research suggests that the relationship between obesity and hypothyroidism goes both ways. Obesity can raise inflammation, which may affect how the thyroid gland works. The good news is that weight loss — especially when it focuses on reducing excess body fat and building muscle — may help improve thyroid function.

If you’re living with both hypothyroidism and obesity, it’s not always clear which came first. Still, addressing both conditions is a smart move for your health.

How Do Thyroid Hormones Affect Metabolism?

Thyroid hormones help regulate your metabolism — the process by which your body turns food into energy. If your thyroid gland is underactive and doesn’t make enough of these hormones, your metabolism can slow down.

This slowdown can be caused by an autoimmune condition, inflammation, certain medications, or other health issues that affect thyroid function. With a lower metabolic rate, your body burns fewer calories than usual. A slower metabolism may lead to weight gain, which may improve once thyroid levels are properly treated.

Thyroid hormones also raise your body temperature, which helps burn more calories, even at rest. People with hypothyroidism tend to feel cold, whereas people with hyperthyroidism (an overactive thyroid gland) may feel hot and sweaty. If you have hypothyroidism, your resting metabolic rate — the number of calories your body uses when not active — tends to be lower.

Can Hypothyroidism Cause Obesity?

Hypothyroidism has been linked to weight gain, but it usually causes only a modest increase — about 5 to 10 pounds. Part of this weight gain comes from extra salt and water in the body.

Thyroid changes alone seldom cause severe obesity (formerly called morbid obesity). Many factors, including genetics, lifestyle habits, and other hormone systems that regulate hunger, stress, and glucose (blood sugar) — also play a role.

Hypothyroidism can cause the following symptoms:

• Constipation
• Depression
• Heavy periods
• Muscle weakness
• Puffy face

These symptoms may affect your energy levels and motivation to stay active and eat well. They can also lead to bloating and water retention, which can make it feel like you’re gaining weight. Getting support from friends, family, or a healthcare provider can make managing hypothyroidism and obesity feel less overwhelming.

Does Obesity Cause Hypothyroidism?

Hypothyroidism can affect anyone, including those who don’t have obesity — a medical condition defined as having a body mass index (a measure of weight relative to height) of 30 or higher. About 5 percent of people in the U.S. over age 12 have hypothyroidism. Many cases go undiagnosed because the symptoms are mild or easy to miss.

According to the National Institute of Diabetes and Digestive and Kidney Diseases, you may have an increased risk of hypothyroidism if you:

• Are over 60
• Are a woman
• Have had thyroid surgery or radiation (for example, to treat thyroid cancer)
• Have certain genetic conditions in your family
• Were recently pregnant

Insulin resistance, type 2 diabetes, and other autoimmune diseases can also increase your chances of developing hypothyroidism.

Obesity is considered a risk factor for overt hypothyroidism, which shows up clearly on lab tests and may cause noticeable symptoms. Obesity is also linked to a milder type known as subclinical hypothyroidism. In this form, thyroid-stimulating hormone levels are abnormal, but thyroid hormone levels remain normal. Treatment decisions for subclinical hypothyroidism depend on your symptoms and overall health — not everyone needs medication.

How Inflammation and Hormones May Link Obesity and Thyroid Function

Scientists are still learning how obesity and hypothyroidism influence each other. One possible link involves cytokines — proteins involved in inflammation — which are often higher in people with obesity. These molecules may interfere with how the body uses iodine, a nutrient that plays an important role in thyroid hormone production.

Another key player is leptin, a hormone that helps regulate appetite, body weight, and body composition. Leptin is produced by fat tissue, so levels tend to be higher in people with obesity. Leptin also interacts with the thyroid, possibly affecting hormone production and the body’s response. It’s possible that leptin is involved in both obesity and thyroid diseases.

What MyObesityTeam Members Say About Hypothyroidism

Members of MyObesityTeam have described their challenges with weight and thyroid disorders. “I am hypothyroid, and that plays a part in my weight also,” one member said. “I try very hard to lose weight, but my willpower is poor. I try not to keep junk food in my house. I do have Diet Pepsi in my fridge, but I have cut down on that to maybe a couple of times a week.”

“I am pretty frustrated. I’ve been increasing my exercise and decreasing my calories, but the scale is stagnating (staying the same) at best,” another member shared. “I have difficulty regulating my thyroid. I’m hypothyroid. My medication may need to be adjusted. I feel like just saying the heck with it. On the positive side, I can see the difference exercise is making in my overall well-being and keeping my joints (bad knees) as flexible as possible.”

How To Manage Obesity in Hypothyroidism

Treating hypothyroidism can help get your metabolism back on track but, on its own, may not lead to significant weight loss. To manage obesity, lifestyle changes — including a healthy diet and regular physical activity — remain essential.

Along with recommending lifestyle changes, your healthcare provider may suggest medications or surgery to support weight loss. The U.S. Food and Drug Administration (FDA) has approved several prescription medications to treat obesity. Your doctor can help choose the right option based on your current medications and overall health.

Bariatric (weight loss) surgery may also be an option. It’s important to understand the potential risks and benefits, as well as the ways surgery could affect your daily life. Research shows that weight loss — whether from low-calorie diets or bariatric surgery — can improve hypothyroidism in people with obesity. That’s encouraging news if you wonder whether losing weight is worth the effort. It is.

Managing Hypothyroidism With Medication

Hypothyroidism can feel like a setback when you’re already trying to manage obesity, but it doesn’t have to be. Most people with hypothyroidism can achieve normal thyroid levels with hormone replacement therapy.

Doctors typically prescribe levothyroxine, a synthetic version of the hormone your thyroid should make naturally. Finding the right dose may take time, and regular follow-up visits are important. Your doctor will monitor your thyroid hormone levels and adjust your medication as needed.

The good news: Treating either hypothyroidism or obesity often helps improve the other. And both steps can improve your overall health.

Talk With Others Who Understand

MyObesityTeam is the social network for people with obesity and their loved ones. On MyObesityTeam, members come together to ask questions, give advice, and share their stories with others who understand life with obesity.

Do you think thyroid dysfunction could be affecting your weight gain or ability to lose weight? Have you considered asking your doctor about a thyroid function test to find out where you stand? Share your thoughts in the comments below or on your Activities page.