Causes of Unexplained Weight Loss

Unexplained or unintentional weight loss may seem a welcome change for some people, but looking into the potential causes is important. Unintentional weight loss may be a sign of a medical condition, such as thyroid problems, lupus, diabetes, or cancer.

With medical evaluation, an underlying condition is found in at least 72% of people who lose weight unexpectedly. That'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 why people experience it, and how your healthcare provider will determine and treat the cause.

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.

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

Unexplained weight loss can happen to anyone, but it is most common in people over the age of 65. In older adults, the annual incidence of unintentional weight loss is around 13%.

Unintentional weight loss is important because it indicates there is a need to look for an underlying cause. It also has significance to overall health. Unexplained and unintentional weight loss can complicate treatment and recovery in other conditions, including coronary artery disease.

What Can Cause Unexplained Weight Loss?

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 main causes of unexplained weight loss are cancer, digestive tract disorders such as inflammatory bowel disease, and mental health-related causes like depression.

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.

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.

Gastrointestinal Conditions

Problems with your gastrointestinal (GI) system can cause weight loss, including conditions such as:

• Peptic ulcer disease
• Crohn's disease
• Ulcerative colitis
• Pancreatitis

Celiac disease is an example of a GI disease that can lead to weight loss. This autoimmune condition causes your body to attack the cells in your small intestine in the presence of gluten, a protein found in wheat and other grains. This can interfere with your body's ability to absorb nutrients.

Diabetes

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.

Hyperthyroidism

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 of roughly 25% of cancer deaths.

Depression

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.

Lupus

Lupus is an autoimmune condition that causes your body's immune system to mistakenly attack healthy cells. Lupus can cause problems with your digestive system and interfere with your body's ability to absorb nutrients.

Loss of appetite is also a common symptom of lupus. Between 17% and 15% of people with this condition experience unintentional weight loss. Most of the time, the weight loss will be noticed before diagnosis. 

Stress

Stressful life events such as divorce, the death of a family member, or financial difficulties can cause you to have a poor appetite, skip meals, or eat less than usual overall. This can lead to unintentional weight loss. If you find that stress is interfering with your quality of life, reach out to family or friends for support or speak to a mental healthcare provider.

Infections

Infections with viruses, bacteria, and parasites are not uncommon causes and include infections such as:

• Tuberculosis
• Endocarditis (infection of the heart valves)
  

Chronic Diarrhea

Chronic diarrhea can deprive your body of nutrients and lead to unintentional weight loss and malnutrition. Since chronic diarrhea is often caused by an underlying condition, you should always see a healthcare provider if you have diarrhea that persists for more than a few days.

Alcohol and Substance Use Disorder

The use of street drugs such as methamphetamine, prescription medications like Adderall, and over-the-counter drugs like laxatives can cause weight loss.

People with alcohol use disorder may have weight loss associated with reduced appetite, nausea, vomiting, or mental health and lifestyle factors.

People who have had alcohol use disorder for a long time may also experience malnutrition as a consequence of advanced liver disease. Chronic liver disease is associated with a number of nutritional problems such as nutrient malabsorption and decreased appetite.

Chronic Obstructive Pulmonary Disease (COPD)

People with COPD often have protein imbalances and other nutritional imbalances along with changes in the way the body turns nutrients into energy. This can cause unintentional weight loss and malnutrition.  

Chronic obstructive pulmonary disease includes conditions such as emphysema, bronchiectasis, and chronic bronchitis.

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.

Neurological conditions

Early weight loss is a common symptom of neurodegenerative disorders such as Parkinson's disease, Alzheimer's disease, and Huntington's disease. Some researchers believe that weight loss in these conditions may be related to changes in protein metabolism in the brain that lead to increased energy requirements.

Medication

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. Some of the most common include:

• Precose (acarbose)
  
• Wellbutrin (bupropion)
  
• Byetta (exenatide)
  
• Prozac (fluoxetine)
  
• Victoza (liraglutide)
  
• Glucophage (metformin)
  
• Glyset (miglitol)
  
• Symlin (pramlintide)
  
• Topamax (topiramate)
  
• Zonegran (zonisamide)

Less Common 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.
  
• Heart failure: This may be caused by a loss of muscle mass linked to weight loss.
  
• Dental problems: 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.
• Poor nutrition: This may be due to poor food choices or not being able to afford enough food.
  

Diagnosis

If you have unintentional weight loss, be ready to give your healthcare team a complete and careful medical history. Along with the physical exam, your healthcare provider will use this information to 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

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.

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.

Procedures

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.
  

Treatment

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 it may require several visits to determine a cause.

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.

Summary

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.