What Causes Unexplained Weight Gain? What to Know

Medically Reviewed By Megan Soliman, MD

If your weight gain doesn’t seem to be explained by your diet or activity levels, it may indicate an underlying health condition. Possible causes include hormonal conditions, heart problems, and medication side effects. Weight increases are often linked to eating more calories than you burn through daily activity.

If your dietary patterns or activity levels haven’t changed, you may feel that your weight gain is unexplained. Alternatively, you may have changed your diet or activity levels but still feel that your weight gain could have another explanation.

Many other factors, such as certain health conditions and medications, can contribute to weight gain. Talk with a doctor if you have questions about weight changes.

This article discusses reasons for unexplained weight gain, including health conditions and solutions.

Hypothyroidism

A doctor uses a stethoscope to listen to someones breathing.
Photography by Eddie Pearson/Stocksy United

Hormonal imbalances can lead to Trusted Source PubMed Central Highly respected database from the National Institutes of Health Go to source weight gain.

For example, hypothyroidism — a condition in which the thyroid gland does not produce enough hormones — can slow metabolism. Metabolism turns food into energy, and a slow metabolism may lead to Trusted Source PubMed Central Highly respected database from the National Institutes of Health Go to source unexplained weight gain.

If you have hypothyroidism, you may also experience:

  • fatigue
  • sensitivity to the cold
  • dry skin
  • slow heart rate

Treatment

Doctors typically treat hypothyroidism with thyroid hormone replacement therapy. This replaces the lack of thyroid hormone to restore your body functions and reduce symptoms.

Learn more about hypothyroidism, including its symptoms, causes, and treatment.

Insulin resistance

Insulin is a hormone essential for regulating blood sugar levels.

Insulin resistance is when your cells do not respond effectively to the insulin hormone, so the body produces more insulin to compensate. These high insulin levels can lead to Trusted Source PubMed Central Highly respected database from the National Institutes of Health Go to source fat storage — particularly around the abdomen. 

Other symptoms of insulin resistance can include:

  • fatigue
  • darkened areas of skin, particularly where the skin folds, such as the neck or groin
  • frequent infections
  • excessive thirst or hunger
  • tingling in the hands or feet

Treatment

Treatment often focuses on diet and lifestyle approaches, including:

  • maintaining a moderate weight
  • increased physical activity
  • eating a diet as recommended by a doctor or a registered dietitian

Read more about the symptoms, causes, and treatment of insulin resistance.

Polycystic ovary syndrome (PCOS)

PCOS is when people assigned female at birth have a high level of androgen hormones. As a result, cysts develop on the ovaries.

PCOS can disrupt typical hormonal regulation and lead to Trusted Source PubMed Central Highly respected database from the National Institutes of Health Go to source insulin resistance and fat storage Trusted Source PubMed Central Highly respected database from the National Institutes of Health Go to source , causing weight gain. 

You may also experience other PCOS symptoms, such as:

  • excess hair growth on the face or body
  • acne
  • infertility
  • thinning hair on the scalp

Treatment

Treatment options for PCOS focus on symptom management, including:

  • following a diet as recommended by a doctor or a registered dietitian
  • getting regular physical activity
  • hormonal contraceptives and other medications

See more about PCOS symptoms, causes, and treatment.

Cushing syndrome

Cushing syndrome is caused by long-term exposure to high levels of the stress hormone cortisol. It can happen when the body produces too much cortisol on its own or when you take corticosteroid medication. 

Cushing syndrome may cause Trusted Source PubMed Central Highly respected database from the National Institutes of Health Go to source weight gain due to increased cortisol levels in the body, which affect metabolism and promote fat storage.

As well as weight gain, other symptoms of Cushing syndrome include:

Treatment

Treatment for Cushing syndrome involves reducing the amount of cortisol in the body. A doctor may recommend:

  • stopping medications that may be responsible
  • starting medications that can help control cortisol production
  • undergoing surgery to remove any tumors that may be responsible

Learn more about Cushing syndrome, including its symptoms, causes, and treatment.

Heart failure

Heart failure is when the heart cannot pump blood effectively enough to meet the body’s needs. Although it is not a common symptom, heart failure can cause Trusted Source American Heart Association Highly respected national organization Go to source unexplained weight gain. This is due to your body retaining more fluid than usual rather than due to higher levels of fat.

Other symptoms of heart failure include:

  • shortness of breath, even during mild activities
  • persistent coughing 
  • swelling in the legs, ankles, and feet
  • fatigue and weakness

Contact a doctor as soon as possible if you have any heart failure symptoms.

Treatment

Treatment options for heart failure can vary depending on how severe your condition is but may include:

  • following a diet as recommended by a doctor or a registered dietitian
  • getting regular physical activity
  • taking medications
  • undergoing surgery to repair the heart or implant heart devices

See more about heart failure, including its symptoms, treatment, and outlook.

Medications

Some medications alter your metabolism or appetite as a side effect. This can cause weight gain without a noticeable change in your diet or activity levels.

Examples of medications that may lead to weight gain include Trusted Source PubMed Central Highly respected database from the National Institutes of Health Go to source some:

  • antidepressants
  • mood-stabilizing or antipsychotic medications
  • antiseizure medications
  • antipsychotic medications
  • blood pressure medications
  • diabetes medications
  • corticosteroids
  • some types of hormonal birth control, such as those that use progestin hormones

Treatment

If your medical team believes your weight gain is due to a medication you take, they may recommend stopping its use or adjusting your dose.

They may also recommend lifestyle approaches, such as a specific diet and regular physical activity.

Do not stop taking a medication or change your dosage before talking with a doctor first.

Underestimating diet and activity

Sometimes, unexplained weight gain is due to unintentionally consuming more calories than your body can burn. This can happen due to:

  • eating larger portions
  • not counting some sources of calories, such as beverages
  • not getting enough physical activity

If you feel you have unexplained weight gain, talk with a doctor. They may ask about your lifestyle and habits and run diagnostic tests for medical conditions.

When to see a doctor

Talk with a doctor if you experience weight gain without a clear cause — especially if you have other symptoms.

Also contact a doctor if you have questions about your weight, diet, or general health.

Read more about health conditions that can cause weight gain.

FAQ

Megan Soliman, MD, has also reviewed the answers to the following frequently asked questions.

What is considered rapid weight gain?

Rapid weight gain is an increase of more than 5% of your body weight over a short period, often less than 6 months.

For example, a 2 to 5 pound Trusted Source PubMed Central Highly respected database from the National Institutes of Health Go to source increase over 3 days may be considered rapid weight gain.

What causes rapid weight gain in females?

Several factors may cause rapid weight gain in females, such as:

Learn about how periods can affect your weight.

Summary

Unexplained weight gain unrelated to diet or activity may indicate an underlying health condition.

Conditions that can cause weight gain include:

  • hypothyroidism
  • PCOS
  • Cushing syndrome
  • heart failure

Medications can sometimes also cause weight gain.

Talk with a doctor if you have questions about weight changes and other symptoms.

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Medical Reviewer: Megan Soliman, MD
Last Review Date: 2024 Jun 25
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