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What Is the Connection Between Thyroid and Weight Gain?

Plus, the Best Lab Tests for Identifying a Thyroid Condition
April 26, 2023
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Unintentional weight gain is one of the most common signs of aging.

According to the Agency for Healthcare Research and Quality, people between the ages of 40-65 tend to gain between 1-2 pounds yearly.

However, unexplained weight gain is also one of the most common signs of a thyroid disorder.

If you’re frustrated by unintentional weight gain you can’t seem to lose, it could be more than just the typical signs of aging. It could be an undiagnosed thyroid disorder.

When your thyroid isn’t functioning well, you’re more likely to store fat instead of burning it for energy.

An underactive thyroid, or hypothyroidism, leads to weight gain in about half of people with this condition. It typically affects people over 60 and is more prevalent in women than men. However, it can affect anyone, including children.

Today we share the connection between an underactive thyroid and weight gain as well as expert guidance on exactly which lab tests you need to confirm your diagnosis.

What Is the Thyroid and What Does It Do?

The thyroid is a small, wing-shaped gland located at the base of the throat, just above the collarbone. It is one of your endocrine glands, which make hormones that control things like mood, growth, and development.

Thyroid hormones also control how fast or slow several activities in your body function, like metabolism, heart rate, and digestion.

What Is the Relationship Between Thyroid and Weight?

Does hypothyroidism cause weight gain? Yes, but it’s complicated.

The medical community doesn’t precisely know the connection between underactive thyroid and weight gain, but there several contributing factors. Thyroid hormones heavily influence metabolism, appetite regulation, and digestion, which could impact your weight.

When you have hypothyroidism, your metabolism slows down, which means you burn less energy—even while at rest. Weight gain and weight loss depend on how many calories we consume versus how many we burn for energy.

What Is the Relationship Between Hypo/Hyperthyroidism and Weight Gain?

You have hypothyroidism when your thyroid gland underproduces the T3 (triiodothyronine) and T4 (thyroxine) hormones. This condition causes your body to use energy slower than it should, leading to frustrating weight gain.

Untreated hypothyroidism also makes it difficult to lose weight despite healthy lifestyle changes (e.g., diet and exercise).

If you have an overactive thyroid, however, your body burns more calories than normal, often resulting in weight loss. This condition is called hyperthyroidism.

Untreated hyperthyroidism can lead to blood clots, stroke, or other heart problems.

What Is the Relationship Between BMR and Weight?

We need to talk about your metabolism to understand the relationship between your basal metabolic rate (BMR), thyroid, and weight gain. Metabolism involves a series of processes that work to break down food and convert it into energy for the body. It also determines how quickly—or slowly—your body uses calories.

Your body uses energy when resting, performing daily activities, or engaging in physical activity. The efficiency at which your body uses energy is called your BMR.

When you have excess energy from consuming more food than your body can use effectively—this energy gets stored in fat cells resulting in weight gain.

Can the Thyroid Be Used to Help Me Lose Weight?

Yes, it is possible to use synthetic thyroid hormone treatments to support weight loss. However, restoring thyroid hormones to a normal range will not lead to significant weight loss.

Most people regain the weight once the treatment stops.

Moreover, using thyroid hormones to help with weight loss increases the risk of adverse consequences like muscle loss, bone loss, and heart problems. 

How Does Hypothyroidism Affect Weight?

Put simply, an underactive thyroid often leads to weight gain because your body stops using calories efficiently. Hypothyroidism also contributes to reduced renal function, leading to excess salt and water accumulation in the blood.

Significant weight gain is rarely associated with hypothyroidism. People with hypothyroidism generally gain between 5-10 pounds, depending on its severity.

Losing Weight With Hypothyroidism

To recap, hypothyroidism can

  • slow body functions, like metabolism,
  • lead to water and salt retention,
  • cause modest weight gain of 5-10 pounds,
  • and make it more challenging to lose weight.

Once you’ve been diagnosed and treated for hypothyroidism and your thyroid hormone levels are restored, your ability to gain or lose weight will improve.

However, it is important to note several factors can lead to weight gain (e.g., lifestyle, genetics, stress, insufficient sleep, and certain health conditions). After hypothyroidism treatment, those with more than ten pounds of excess weight may not experience much weight loss.

Symptoms of an Underactive Thyroid

The symptoms of hypothyroidism typically develop slowly; for some, it can be years before they’re noticeable. They can include:

  • Unintentional weight gain
  • Fatigue
  • Muscle weakness
  • Numbness or tingling in the hands
  • High cholesterol
  • Cold intolerance
  • Dry skin, nails, and hair
  • Low libido
  • Heavy menstruation
  • Brain fog

If you think there is a connection between your thyroid and weight gain, get the insights you need to make informed decisions about your health.

We recommend a comprehensive selection of tests to give you the most accurate picture of your thyroid health and help you identify whether it contributes to your weight gain.

Take the first step toward restoring your thyroid hormone levels and controlling your weight when you order these key lab tests:

Our physician-approved thyroid lab tests are convenient, affordable, and confidential. Results are typically available within 1-2 business days.

Doctor's orders are never required. Quest Diagnostics conducts all tests.

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