Causes of Unintentional Weight Loss

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Unexplained or unintentional weight loss might be welcomed by some people, but asking about the potential causes is extremely important. Unintentional weight loss can have underlying causes ranging from thyroid problems to infections to cancer, and always warrants an investigation.

With medical evaluation, an underlying condition is found in as many as 74% of people who lose weight unexpectedly. What exactly defines this type of weight loss, what are the potential causes. and what can you expect as you and your doctor seek to determine the cause?

common causes of unexplained weight loss

Ellen Lindner / Verywell

Unintentional Weight Loss Definition

Unexplained weight loss is defined as the unintentional loss of at least 10 pounds or 5% of body weight over a period of 6 to 12 months. This would be equivalent to a 200-pound man losing 10 pounds or a 130-pound woman losing 6 to 7 pounds.

The weight loss occurs without an intention to lose weight, such as a conscious change in the calories you consume or beginning an exercise program.

Weight loss may occur because you are eating less, or because your body is using nutrients differently due to a change in your metabolism or the growth of a tumor.

When to See Your Doctor

If you are losing weight without trying it is important to make an appointment to see your doctor, even if you think there is an explanation for your weight loss. It's important to be your own advocate and continue to ask the question "why" if you don't feel you have an adequate explanation. Ask for a second opinion if needed.

Many of the conditions which can lead to unintentional weight loss are difficult to diagnose in the early stages, and sometimes a number of blood tests or imaging studies are needed to define the cause.


There are many reasons for unexplained weight loss, some serious, and some more of a nuisance. In older adults (over the age of 65) the most common cause is cancer, followed by gastrointestinal and psychiatric conditions.

Around 40% of people with cancer state that they had experienced weight loss at the time of diagnosis. A 2018 study found that unintentional weight loss was the second-highest predictor for some types of cancer.

An overview of some causes include:

  • Endocrine conditions: Conditions such as hyperthyroidism (overactive thyroid), hypothyroidism (underactive thyroid), diabetes, and Addison’s disease.
  • 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).
  • 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) recurs.
  • Intestinal problems: These include peptic ulcer disease, celiac disease, Crohn's disease, ulcerative colitis, and pancreatitis.
  • Heart failure
  • Kidney failure
  • 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
  • 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 finances that limit the purchase of food (starvation).
  • Psychological conditions: These include as depression and anxiety.
  • 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.


If you have unintentional weight loss, your doctor will first take a careful history, looking for risk factors for many medical conditions, and then will perform a physical exam. Depending on her findings, she may recommend further tests and radiology studies. 

Questions Your Doctor May Ask

Be prepared to answer these questions:

  • When did you first notice that you were losing weight?
  • How fast have you been losing weight?
  • Have you made any changes to your diet or exercise schedule?
  • Have you ever had weight loss like this before?
  • How upsetting is the weight loss to you?
  • Are you having any other symptoms such as palpitations, shortness of breath, jaundice (a yellowish discoloration of the skin), a persistent cough, hoarseness, thirst, or sensitivity to cold or heat?
  • How would you describe your general health compared to, say, a year ago?
  • Have you had screening tests recommended for someone your age such as a mammogram or colonoscopy, and what were the results?
  • Have you had any nausea or vomiting? Do you ever make yourself vomit?
  • Have you been constipated or had diarrhea?
  • 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

Blood tests your doctor orders will depend on many factors, including any symptoms you are having. Tests that are commonly done include:

  • Complete blood count (CBC): A CBC can reveal evidence of infections, anemia (that can be caused by many conditions that result in unintentional weight loss), 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: A sodium, potassium, 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 can be thought of as an ultrasound of the heart, and 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 regards to health. Cancer cachexia is a condition of unintentional weight loss combined with a few other concerns and is directly responsible for around 20% of cancer deaths.

Even with coronary artery disease, it has been found that outcomes were 62% worse for people who experience unintentional weight loss.

Unintentional weight loss is linked with higher morbidity (development of illnesses), a higher mortality (higher death rate), and a lower quality of life for people suffering from many diseases.


The treatment of weight loss that isn’t intentional will depend upon the underlying cause or causes. Given the high likelihood of an underlying cause of the weight loss, anyone who has experienced weight loss without trying should have a thorough history and physical performed, in addition to other needed studies.

Some of the causes of unintentional weight loss are fairly uncommon, and this may require several visits to determine a cause.

Regardless of the cause, measures should be taken to treat the weight loss as well. When a cause is determined, the weight loss itself is sometimes pushed to the back burner. If this is you, make sure to talk to your doctor about how you should treat this symptom.

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.

Treatment of weight loss can, in turn, help people tolerate treatments for whatever the condition is that has caused weight loss.

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Article Sources
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