Causes of Unintentional Weight Loss

Unexplained or unintentional weight loss may seem a welcome change for some people, but asking about the potential causes is important. Unintentional weight loss may be a sign of a medical condition, and these potentially serious causes can range from thyroid problems to cancer.

With medical evaluation, an underlying condition is found in at least 72% of people who lose weight unexpectedly. It's why unexplained weight loss should always be a reason to talk to your healthcare provider.

This article looks at weight loss you don't expect to see, some reasons for why people experience it, and what happens as you and your healthcare provider work together to find and treat the cause.

common causes of unexplained weight loss

Verywell / Ellen Lindner

Unintentional Weight Loss Definition

Unexplained weight loss is defined as the unintentional loss of at least 5% of body weight over a period of six to 12 months. This would mean a 10-pound loss in a 200-pound man, or losing between 6 and 7 pounds for a 130-pound woman.

The weight loss occurs without any attempt to lose weight, such as cutting the calories you eat or starting to exercise.

When to See Your Healthcare Provider

Many conditions that lead to unintentional weight loss are difficult to diagnose in the early stages, and sometimes a number of blood tests or imaging studies (such as X-rays) are needed to find the cause.

It is important to see your healthcare provider if you are losing 5% to 10% of your weight without trying, even if you think there is an explanation for your weight loss. Continue to ask the question "why" until you feel confident you have the answer, and don't be afraid to ask for a second opinion if needed.


There are many reasons for unexplained weight loss, some of which are serious. For adults not living in a nursing home or other care setting, the most common reasons are cancer, digestive tract disorders such as inflammatory bowel disease, and mental health-related causes like depression.

Around 40% of people with cancer said they had experienced weight loss at the time of diagnosis. A 2018 study found this weight loss was the second-strongest predictor of some types of cancer.


Weight loss may be the first sign of blood-related cancers such as leukemias and lymphomas, or solid tumors such as lung cancer (especially adenocarcinoma of the lung), colon cancer, ovarian cancer, and pancreatic cancer. Weight loss can also occur when an early-stage tumor (such as breast cancer) comes back.


People with diabetes usually fall into two categories: Type 1, which is an autoimmune disease, and Type 2, which often develops later in life when the body can't make or process insulin properly. (A third type, called gestational diabetes, is temporary and occurs only during pregnancy.)

Unexplained weight loss can occur with both types but is more common in Type 1 diabetes.


There are several conditions that cause hyperthyroidism, a condition in which the thyroid gland in the neck is overactive. They include autoimmune disorders such as Graves' disease, the most common cause of hyperthyroidism in the United States. Iodine exposure, medication error, and even pregnancy also may cause an overactive thyroid.

Hyperthyroidism speeds up your metabolism, which can lead to weight loss.

Muscle Loss

Weight loss may be linked to the loss of comparatively heavy muscle tissue, sometimes called muscle atrophy or muscle wasting. That's especially true in cancer and in people diagnosed with HIV/AIDS, and is known as cachexia in these groups. This muscle loss can prove fatal, and is the underlying cause in roughly 25% of cancer deaths.


Depression can cause changes in eating habits that can lead to weight loss or weight gain. Depression affects many people from all walks of life, and roughly one in every six people will experience depression at some point in their lives.

Addison’s Disease

Addison's disease is an endocrine disorder that is related to problems with the adrenal glands found atop each kidney. These glands produce key hormones, or chemical messengers, like cortisol. The lack of these hormones in Addison's disease may be the cause of weight loss, fatigue, and other symptoms.

Rheumatoid Arthritis

Rheumatoid arthritis (RA) is best known for causing joint pain and damage, but it also can bring on muscle wasting and weight loss known as rheumatoid cachexia. RA may be related to inflammation of the digestive system and gastrointestinal disease, which may contribute to unintentional and unexplained weight loss.

Other Causes

  • Hypothyroidism: This disorder is caused by an underactive thyroid and is the opposite of hyperthyroidism, although it also can sometimes contribute to weight loss.
  • Infections: Infections with viruses, bacteria, and parasites are not uncommon causes and include infections such as HIV/AIDS, tuberculosis, and endocarditis (infection of the heart valves).
  • Intestinal problems: These include peptic ulcer disease, celiac disease, Crohn's disease, ulcerative colitis, and pancreatitis.
  • Heart failure: This may be caused by a loss of muscle mass linked to weight loss.
  • Kidney failure: Poor appetite and nausea may contribute to weight loss, but so does a change in fluid retention in a person whose kidneys aren't working properly.
  • Chronic obstructive pulmonary disease (COPD): COPD includes conditions such as emphysema, bronchiectasis, and chronic bronchitis.
  • Oral concerns: These include gum disease, tooth decay, mouth sores, or braces.
  • Smoking: Weight loss in smokers is often related to changes in metabolism, or the way your body processes and absorbs what you eat and drink.
  • Eating disorders: Both anorexia nervosa and bulimia can cause weight loss, and people who are coping with these conditions may not realize the significance of their weight loss.
  • Poor nutrition: This may be due to poor food choices or not being able to afford enough food.
  • Medications: Nearly any medication may have weight loss as a consideration or side effect. Medications may cause weight loss directly, or cause nausea and loss of appetite leading to weight loss.
  • Drug abuse: Not only street drugs such as methamphetamine, but prescription medications like Adderall and over-the-counter drugs like laxatives may be abused.
  • Neurological conditions: These include Parkinson’s disease and Alzheimer's disease.

Weight Loss Causes in Men and Women

Both men and women may have unintended or unexplained weight loss. Some autoimmune disorders, like RA and Graves' disease, occur more often in women. Eating disorders and depression happen more frequently in women, as does pregnancy-related weight loss. Men face risks due to cancer cachexia, digestive problems, and infections like endocarditis.


If you have unintentional weight loss, be ready to give your healthcare team a complete and careful medical history. Along with the physical exam, it's how a healthcare provider will determine your risk factors and narrow the possibilities for underlying medical conditions.

Questions Your Healthcare Provider May Ask

Be prepared to answer questions including:

  • When did you first notice that you were losing weight?
  • Have you made any changes to your diet or exercise schedule?
  • Are you having any other symptoms such as shortness of breath or excessive thirst?
  • Have you had a colonoscopy or other screening tests, and what were the results?
  • Have you felt depressed or stressed lately?
  • Do you have any dental problems that pose difficulties with eating?
  • Are there any illnesses that run in your family?

Tests and Labs

The blood tests that your healthcare provider orders will depend on many factors, including any symptoms. Tests that are commonly done include:

  • Complete blood count (CBC): A CBC can show evidence of infections, anemia (a lack of red blood cells that can be caused by many conditions), and more.
  • Thyroid panel
  • Liver function tests
  • Kidney function tests
  • Blood sugar (glucose)
  • Urinalysis
  • Tests for inflammation: Non-specific tests may include a sed rate and/or C-reactive protein.
  • Electrolytes: Levels of sodium, potassium, and calcium may give clues to an underlying problem.


Endoscopy procedures such as an upper GI endoscopy or colonoscopy can look for evidence of gastrointestinal causes of weight loss.

An echocardiogram is an ultrasound of the heart, and it is helpful in diagnosing many conditions, including infections present on the heart valves (infectious endocarditis).

Imaging Studies

Imaging tests that may be helpful include:

  • Chest X-ray (it's important to note that a plain chest X-ray can miss conditions such as lung cancer)
  • Computerized tomography (CT) scan of the chest or abdomen.
  • Magnetic resonance imaging (MRI)
  • Positron emission tomography (PET) scan can look for evidence of metastases from cancer.


Unintentional weight loss is important not only in looking for an underlying cause but because of what it means in overall health. Unexplained and unintentional weight loss also can complicate treatment and recovery in other conditions, including coronary artery disease.

Some of the underlying causes that contribute to unintentional weight loss are serious conditions in their own right. Seeing a healthcare provider and having the necessary tests will help determine the best course of action and hopefully better outcomes. That's because the weight loss itself is linked with higher mortality (death rate) and a lower quality of life for people who have these illnesses.


The treatment of unintentional weight loss will depend upon the underlying cause or causes, and it's highly likely there is one. Some of the causes of unintentional weight loss are fairly uncommon, and this may require several visits to determine a cause.

What's important is that the weight loss be treated, too. When the exam, blood tests, and other procedures lead to a specific cause, it's easy to focus on that treatment while the weight loss itself is set aside. Make sure to talk to your healthcare provider about how you should treat the weight loss.

For those who are diagnosed with cancer, a palliative care consultation should be considered. Palliative care teams do an excellent job of addressing concerns not directly related to cancer (for example, chemotherapy or radiation therapy) such as unintentional weight loss.


Unexplained weight loss may not seem a cause for concern, and it's easy to ignore. But this kind of weight loss likely is a clue to an illness that needs to be diagnosed and treated. Your healthcare provider can help find the cause, and treat both the underlying condition and the weight loss.

Frequently Asked Questions

  • What is the most common reason for unintentional weight loss?

    It appears to depend in part on age. For example, in a study of 2,677 people with unexplained weight loss whose average age was 64, cancer was most often responsible. A similar study of people 65 and older homed in on nonmalignant causes, including diminished sense of taste and appetite due to medication.Still other research has found up to a quarter of cases of unintentional weight loss can't be explained.

  • When should you worry if you start losing weight without trying?

    Any number of pounds lost is a potential concern. However, unintentional weight loss is defined as a loss of 10 pounds or 5% of total body weight within six to 12 months—especially among people 65 and older, for whom the condition is most common.

  • What types of cancer most often cause weight loss?

    The type of weight loss typical among cancer patients—cachexia, in which both muscle mass and fat are lost—is most often associated with cancer of the pancreas, stomach (gastric cancer), lung, esophagus, colon, and head or neck.

13 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Additional Reading

By Lynne Eldridge, MD
 Lynne Eldrige, MD, is a lung cancer physician, patient advocate, and award-winning author of "Avoiding Cancer One Day at a Time."