Unexplained Weight Loss – 18 Common Medical Causes

Published on June 12, 2024
Unexplained Weight Loss - 18 Common Medical Causes

Losing weight without trying might sound awesome, huh? But, guess what? It’s not always as cool as it seems. Imagine ditching the workout and still getting slimmer – sounds like a win, right? But it could actually mean there’s something wrong. Yep, diseases can swipe pounds off you when you least expect it. Hang with me here, and I’ll spill the beans on why you might be shedding pounds without saying ‘go’. It’s one of those surprises nobody wants, and trust me, you’re gonna want to hear this.

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.

In this article, we’ll discuss more information about the basics and the potential causes of your unexplained weight loss. But remember, you may wish to not self-diagnose. Visit your doctor for a proper diagnosis.

What Is Unexplained Weight Loss?

Unexplained weight loss is a noticeable drop in body weight that occurs even if you are not trying to lose weight. Weight loss does not come about because of diet, exercise or lifestyle changes. Weight loss of 10 pounds or more, or 5% of body weight, over a period of 6 to 12 months should be a red flag.

As mentioned earlier, this can be due to a number of things. It might be a symptom of a serious condition or illness. For this reason, it is important to seek medical attention if you have weight loss that cannot be explained.

Who Is At Most Risk?

While unexplained weight loss can occur to anyone, it is most common and most serious in the elderly. Even an unexplained weight loss of < 5% of body weight can be a sign of a serious health condition in people who are 65 years old and older.

Top 18 Medical Causes of Unexplained Weight Loss

1. Poor Nutrition

As many as 50% of hospital patients worldwide have poor nutrition and are at risk of malnutrition (1). They are not getting the nutrients they need in the right amounts. If malnutrition goes on long enough, it can have a significant impact on your health, including unexplained weight loss.  While older adults are at risk because of medications, natural appetite loss or food insecurity, a nutritionally imbalanced diet can contribute to malnutrition in younger, presumably healthy people. The best way to prevent malnutrition is to eat well-balanced meals with the right mix of protein, fat, and carbohydrates.

2. Muscle Loss or Sarcopenia

People age 40 and above tend to experience muscle loss. It progresses more rapidly after the age of 75 (2). While hormonal changes can contribute to how your body builds and stores muscle as you age, most cases of sarcopenia are linked to poor nutrition as well as inactivity. One of the best ways to prevent and treat muscle loss is to add more protein and vitamin D to your diet. Older adults often require more protein to build the same amount of muscle, since the body becomes less efficient at processing proteins.

Diets that are heavy in acid-producing foods such as meat and low in fruits and vegetables have been shown to have deleterious effects on muscle mass. Adding weights to your workout routines also helps build muscle mass and strength.

3. Hyperthyroidism or Overactive Thyroid

Unexplained weight loss could be a sign of hyperthyroidism. The thyroid gland produces excessive amounts of the thyroid hormone, which controls many functions in the body, including metabolism. If your thyroid is overactive, you’ll quickly burn calories even if you have a good appetite. The result can be an unintentional weight loss.

Weight loss is just one of a constellation of symptoms of hyperthyroidism including heart palpitations, anxiety, fatigue, sleep problems, hand tremors, heat intolerance, hair loss, insomnia, and light periods in women.

Possible causes of hyperthyroidism include Graves’ disease, thyroiditis, eating too much iodine, and taking too much thyroid medicine. A simple blood test can detect hyperthyroidism. Also, these conditions are all treatable. Whatever the cause of your hyperthyroidism, there is a treatment that can help reverse the symptoms.

4. Peptic Ulcer Disease

Unexplained weight loss is one of 10 signs of an ulcer you should never ignore. Peptic ulcers are open sores that develop on the inside lining of the stomach as well as on the upper portion of the small intestine. Because the main symptom of peptic ulcers is stomach pain, they often cause loss of appetite (3).

Lifestyle modifications in combination with different medications are the best way to treat the condition and any weight loss associated with it.

5. Diabetes

Type 2 diabetes is often associated with weight gain or obesity, but weight loss may be a surprising diabetes symptom. When the body is not using the hormone insulin properly, glucose no longer makes its way into the bloodstream to be used as energy. When there is an insufficiency in insulin, the body starts burning fat and muscle for energy, causing a reduction in overall body weight.

Diabetes is diagnosed through simple blood testing. See your doctor if you are concerned. Preventing type 2 diabetes is still your best bet, and improving your eating habits can help you do just that!

6. Depression

Weight loss may be a side effect of depression, which is defined as feeling sad, lost, or empty for at least two weeks. These emotions interfere with daily activities, such as going to work or school.

The symptoms vary from person to person. One of the many side effects of this debilitating disease is a loss of appetite, which naturally causes a person to lose weight.

Other symptoms of depression include constant sadness, loss of interest in hobbies, low energy, sleeping problems, thoughts of death or suicide, irritability, and poor concentration.

While there’s no one single cause of depression, many cases can be treated effectively with medication and therapy—although some antidepressants can also contribute to further weight loss.

7. Dementia

It makes sense that people in the advanced stages of Alzheimer’s disease and other forms of dementia often lose weight as they are unable to communicate their food needs. But other factors contribute too. Those with dementia can become socially isolated or simply forget to eat regularly. The breakdown of neurons in the brain dulls the senses of taste and smell, so food becomes less appealing. In fact, the evidence shows that older people who experience significant weight loss could be raising their risk of developing dementia (4). Check out these 16 hidden signs you’re not as healthy as you think.

8. Congestive Heart Failure

Approximately 5.7 million adults in the United States have heart failure (5). It occurs when the heart is unable to pump enough blood and oxygen to the heart and the rest of the body, and an important indicator of this condition can be rapid unexplained weight loss, known as cardiac cachexia (6). It’s a loss of at least 7.5% of normal weight within six months.

9. Inflammatory Bowel Disease

Unexpected weight loss may be a symptom of inflammatory bowel disease (IBD). IBD is a term that encompasses several chronic inflammatory disorders of the digestive tract. The two most common types are Crohn’s disease and ulcerative colitis. Severe intestinal inflammation such as active IBD is associated with decreased nutrient absorption and significant weight loss (7).

The chronic inflammation of IBD also puts your body in a catabolic state, which means that it’s constantly using up energy. It likewise disrupts ghrelin, the hunger hormone, and leptin, the satiety hormone, further contributing to weight loss by decreasing appetite.

Other symptoms of IBD include diarrhea, stomach pain, bloating, bloody stools, and fatigue. These symptoms are triggered by certain foods. If you have IBD, you might be hesitant to eat. Treatment of IBD usually consists of nutritional support, medication, and in some cases, surgery.

10. Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is a progressive lung disease. This includes emphysema and chronic bronchitis. Many people with COPD have both.

Emphysema slowly damages the air sacs in your lungs, making it hard to breathe. Chronic bronchitis causes inflammation of the airways that bring air to your lungs. This produces mucus, coughing, and breathing issues.

Early COPD is mild. Some people may not show symptoms but those that may appear include shortness of breath, wheezing, chest tightness, and mild coughing with or without mucus.

Cachexia and muscle wasting are frequent but partly reversible complications in patients with COPD and affect disease progression and prognosis. Weight loss in COPD is a consequence of increased energy requirements unbalanced by dietary intake (8). Also, labored breathing burns many calories. Patients with COPD may need 10 times more calories to breathe than a person without COPD (9). It can also feel uncomfortable to eat and breathe at the same time.

Other symptoms of severe COPD also include swelling of legs, ankles, or feet, low muscle endurance, and fatigue.

The main cause of COPD is cigarette smoking. Long-term exposure to irritants such as air pollution and dust can also lead to COPD. Treatment includes medications, such as bronchodilators, and lung therapies, like oxygen therapy.

11. Celiac Disease

Celiac disease is an autoimmune disorder aggravated by chronic exposure to gluten that causes damage to the small intestine. Gluten is a protein in wheat and other grains. When celiac is at its worst, it destroys the lining of the intestine, which causes people to stop absorbing nutrients and, over time, stop absorbing calories as well.

Also, aside from tetany, lightheadedness, and hypocalcemia, patients with celiac disease often present with diarrhea and vomiting, causing dehydration and weight loss (10).

12. Tuberculosis

Another cause of unexplained weight loss is tuberculosis (TB), a contagious condition that usually affects the lungs. It’s caused by Mycobacterium tuberculosis bacteria. A decreased appetite is one of the major symptoms of TB. There can be nutrient malabsorption, micronutrient malabsorption, and altered metabolism leading to wasting (11).

TB spreads through the air. You can catch TB without getting sick. If your immune system can fight it, the bacteria will become inactive. This is called latent TB. Over time, it can turn into active TB. If this happens, you’ll soon start to experience a bad cough that lasts 3 weeks or more, chest pain, coughing up blood or phlegm, fatigue, night sweats, chills, and fever.

Some people are at risk for active TB. This includes people with weak immune systems. TB is typically treated with a course of antibiotics for six to nine months.

13. Lupus

Similar to RA, lupus is also an autoimmune disease. Unfortunately, it wreaks havoc throughout the body, from kidney damage to GI disruption to rashes. Often, people with lupus experience weight loss due to loss of appetite, unhealthy dietary habits, or decreased energy and mobility (12).

Lupus can also cause acid reflux. Patients will feel burning pain in the chest area, often after eating, which in turn causes some patients to avoid food. The gastrointestinal problems that often accompany lupus, including stomach cramps and diarrhea, further cause weight loss, as well as the medications used to treat it.

14. Addison’s Disease

Addison’s disease develops when the immune system attacks the adrenal glands. In turn, the adrenal glands can’t make enough hormones like cortisol and aldosterone. Cortisol regulates many functions, including metabolism and appetite (13). Low levels of cortisol may lead to poor appetite and weight loss.

Other symptoms of Addison’s disease include low blood pressure, chronic fatigue, muscle weakness, salt cravings, and hyperpigmentation.

Addison’s disease is rare, affecting roughly 1 in 100,000 people in the United States (14). Treatment includes medications that’ll regulate your adrenal gland.

15. Zinc Deficiency

Your body needs numerous vitamins and minerals, including zinc, to operate at its best. Many people in the US get enough zinc through food, but for those who don’t, a deficiency can cause a decrease in appetite and weight loss (15). Zinc deficiency causes a constant bad taste in your mouth, which leads to not eating and losing weight.

Zinc deficiency can occur as a result of taking certain medications, including some antibiotics, and certain diuretics prescribed for high blood pressure. Vegetarians are also at risk for zinc deficiency as meat is a good source of zinc. Other excellent sources of zinc include oysters, red meat, poultry, beans, and nuts.

16. Parasites

People pick up tapeworms, roundworms, hookworms, and other parasites usually after ingesting contaminated food or water. The parasites busy themselves absorbing nutrients in the body and reproducing. Parasites can take weeks and months, sometimes years, to reveal themselves. Eventually, nausea, vomiting, diarrhea, and loss of appetite set in, causing weight loss.

17. Cancer

Cancer is a general term for diseases that cause abnormal cells to quickly divide and spread. According to experts, one of the first signs may be an unexplained weight loss of 10 pounds or more (16). This is common with cancers of the pancreas, lung, stomach, and esophagus.

Cancer also increases inflammation. This promotes muscle wasting and disrupts appetite-regulating hormones. A growing tumor may also increase your resting energy expenditure (REE), or how much energy your body burns at rest.

Treatment depends on the type of cancer. Typical treatments include surgery, radiation therapy, chemotherapy, and immunotherapy.

18. Eating Disorders

Most eating disorders involve focusing too much on your weight, body shape, and food, leading to dangerous eating behaviors. These behaviors can significantly impact your body’s ability to get appropriate nutrition. Anorexia nervosa and bulimia nervosa are two of the most common eating disorders. 

Anorexia is a potentially life-threatening eating disorder characterized by an abnormally low body weight, intense fear of gaining weight, and a distorted perception of weight or shape. You excessively limit calories or use other methods to lose weight, such as excessive exercise, using laxatives or diet aids, or vomiting after eating. 

Efforts to reduce your weight, even when underweight, can cause severe health problems, sometimes to the point of deadly self-starvation. Starvation affects the brain and influences mood changes, rigidity in thinking, anxiety, and a reduction in appetite.

With Bulimia nervosa, you typically eat a large amount of food in a short time and then try to rid yourself of the extra calories in an unhealthy way. Because of guilt, shame and an intense fear of weight gain from overeating, you may force vomiting or you may exercise too much or use other methods, such as laxatives, to get rid of the calories.

Key Takeaway

While it is normal for your body weight to fluctuate, losing weight without changing your habits should give you a sign that something else might be going on.

If you experience a 5% weight loss in 6 to 12 months, or if you notice any of the above symptoms, see your doctor immediately. 


  1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4596423/
  2. https://www.iofbonehealth.org/whos-risk-0
  3. https://www.ncbi.nlm.nih.gov/pubmed/17956071
  4. https://bmjopen.bmj.com/content/9/5/e021739
  5. https://www.cdc.gov/heartdisease/heart_failure.htm?CDC_AA_refVal=https%3A%2F%2Fwww.cdc.gov%2Fdhdsp%2Fdata_statistics%2Ffact_sheets%2Ffs_heart_failure.htm
  6. https://www.mountsinai.org/health-library/report/heart-failure
  7. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5256970/
  8. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4936454/
  9. https://my.clevelandclinic.org/health/articles/9451-nutritional-guidelines-for-people-with-copd
  10. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4978208/
  11. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2813110/
  12. https://www.hopkinslupus.org/lupus-info/lifestyle-additional-information/lupus-diet/
  13. https://www.todaysdietitian.com/newarchives/111609p38.shtml
  14. https://rarediseases.org/rare-diseases/addisons-disease/
  15. https://ods.od.nih.gov/factsheets/Zinc-Consumer/
  16. https://www.cancer.org/cancer/cancer-basics/signs-and-symptoms-of-cancer.html
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