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Unexplained Weight Loss - Causes, Diagnosis, and Treatment

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5 min read


Unexplained weight loss is the decline in body weight when people are not aiming to lose weight. This article explores the reasons for unexplained weight loss.

Medically reviewed by

Dr. Muhammad Zubayer Alam

Published At January 24, 2023
Reviewed AtApril 1, 2024


Weight loss may be due to many reasons; it can be due to physiological reasons, dieting, exercise, starvation, loss of appetite, or decreased intake of nutrition. However, weight loss mostly happens in old age. Weight loss of more than five kg over six months is significant and may be due to an underlying disease. Hospital and general practice weight records may be valuable in confirming that weight loss has occurred, and if it happens, people should be concerned about the condition. Therefore, reweighing should be done at intervals as sometimes weight is regained or stabilized in those with no apparent cause. Weight loss can be due to several underlying diseases, such as gastrointestinal, systemic, psychiatric, or advanced diseases of many organ systems.

What Is Unexplained Weight Loss?

Unexplained weight loss means loss of four to five kilograms or losing five percent of body weight over six to twelve months unintentionally. Unexplained weight loss is the decline in a person's body weight when a person is not aiming to lose weight. It can occur in any age group, but older people (60 to 70year) are mostly affected. Many people lose weight for many reasons, but when people's weight decreases for an unknown reason (when people did not try to lose weight), it is something to be concerned about health. Therefore, people suffering from unexplained weight loss need medical help.

What Are the Causes of Unexplained Weight Loss?

The following are the causes of unexplained weight loss:

1) Physiological Causes - Weight loss can occur without a severe disease in a healthy individual with a social issue or a change in physical activity. If it occurs in older patients, it is challenging to make an accurate diagnosis, as older people can lose weight because of insufficient food. A patient with a poor dietary history can also lose weight. In such cases, professional help from a dietician is recommended.

2) Psychosocial Causes - Some social factors can affect a person's behavior which causes weight loss. They can be due to the following;

  1. Starvation.

  2. Eating disorders.

  3. Chronic pain due to underlying disease.

  4. Sleep deprivation.

  5. Alcoholism.

3) Psychiatric Illness - Some mental disorders can also affect weight. These include -

  1. Features of anorexia nervosa (an illness precipitated by weight loss due to dieting, increased exercise, or physical condition).

  2. Bulimia (a disorder of abnormal eating behavior).

  3. Mood disorders.

  4. Depression.

  5. Bipolar illness (a mental disorder that causes extreme mood swings).

  6. Grief (a state of being sad even without reason).

4) Systemic Disease - Weight loss can be due to underlying systemic diseases. Some of them are:

Chronic Infection - An infection characterized by prolonged duration, a delayed onset, and slow progression is called a chronic infection, such as tuberculosis (an infection affecting the lungs). It includes a range of parasitic and protozoan infections causing weight loss. A history of foreign travel, high-risk activities (workers in hospitals), and specific features, such as fever, night sweats, shivering, productive cough, and pain in urination, suggests underlying chronic infection.

Respiratory Diseases - Weight loss can be caused by a recurrent chest infection. Following are the respiratory diseases causing weight loss:

  • Tuberculosis (an infection affecting the lung).

  • Chronic obstructive pulmonary disease (a respiratory disease that obstructs airflow passage of lungs and causes breathing problems).

  • Empyema (collection of pus in the lung cavity).

  • Pneumonia (lung infection caused by bacteria or virus).

Renal Diseases - Weight loss can be caused by recurrent urinary infections. Following are the disease affecting the kidney which causes weight loss:

  • Chronic renal failure (a disease associated with deprivation of kidney function causing kidney failure).

  • Salt-losing nephropathy (a disease that causes kidney failure).

Cardiac Diseases - Heart disease may also cause weight loss, such as:

  • Congestive cardiac failure (a chronic heart disease in which heart muscles are weakened and unable to pump blood efficiently, causing heart failure).

  • Infective endocarditis (an infection that causes inflammation of the heart lining).

Endocrine Diseases - These are a group of diseases that affect endocrine glands (the glands that secrete hormones). Endocrine disorders alter the hormone level in the body. Weight loss is noted in a few endocrinal diseases, such as:

  • Type one diabetes (a disease that causes high sugar levels in the blood).

  • Thyrotoxicosis (a disease that causes increased thyroid hormone in the blood)

  • Addison disease (an endocrine disorder characterized by low production of certain hormones).

Neurodegenerative Diseases - The degeneration in the structure and function of neurons is called neurodegenerative disease, which causes weight loss. A few examples of such diseases include the following -

  • Parkinson's disease (a disorder that affects the nervous system and damages nerve cells in the brain).

  • Dementia (memory loss).

  • Motor neuron disease (a disorder that affects motor neurons, causing muscle weakness).

Rheumatological Diseases - Chronic inflammatory diseases affecting joints are often associated with weight loss, such as:

  • Rheumatoid arthritis (An inflammatory disease of joints).

  • Polymyalgia rheumatic (An inflammatory disease that causes stiffness of muscles).

  • Connective tissue disease (a disease that affects that part of the body that connects another part).

  • Systemic sclerosis (a disease that affects the skin and alters the function of internal organs).

  • Systemic lupus erythematosus (a disease that causes harm to its tissues or body).

Gastrointestinal Disease - Most gastrointestinal diseases can cause weight loss. It causes weight loss due to an obstruction in the food passage, which affects food intake. A few examples of such diseases include the following -

  • Dysphagia - A condition in which a person experiences pain in swallowing food.

  • Malabsorption - Improper absorption of food due to abnormal digestive system function, leading to profound weight loss with specific nutritional deficiency.

  • Inflammatory Bowel Disease - Inflammatory disease of the intestine causes anorexia, fear of eating, and loss of protein, blood, and nutrient from the gut, such as Crohn's disease (inflammation of the small intestine) and ulcerative colitis (inflammation of the large intestine).

  • Chronic Infection - Infections, such as diarrhea, a conditions in which the body's solid waste is more liquid than usual and comes out more often.

5) Sexual Diseases - Sex with multiple partners increases the risk of transmission of sexually transmitted diseases (STDs), and drug misuse suggests HIV-related (human immunodeficiency viruses) illness. Acquired immunodeficiency syndrome (AIDS) can cause weight loss of 10 % of total body weight within a month.

6) Metabolic Disorders - Weight loss is associated with metabolic disorders. This disorder alters the body's normal functioning, such as diabetes and hemochromatosis (a condition that limits iron absorption in the body).

7) Malignancy - Weight loss is a late feature of cancer, but it is noticed when patients present other features of cancer. Occult cancer (cancer in which the primary site is unknown) may be responsible for weight loss, especially in the case of small cell carcinoma.

What Are the Tests for Unexplained Weight Loss?

If the cause of weight loss is not identified after taking a thorough history of the patient and after a physical examination, the following investigations are indicated:

  • Blood Tests- Complete blood count will show levels of inflammation which may be raised in unsuspected infections such as tuberculosis, connective tissue disorders, and cancer. Random blood sugar tests may be indicative of diabetes.

  • Fecal Calprotectin- This test will identify gastrointestinal diseases.

  • Urine Test - The findings, such as high glucose level or protein in the urine, indicate diabetes or urinary tract infection, respectively.

  • Computed Tomography (CT- Scan) - Abdominal and pelvic imaging by CT scan is rarely required. The patient's history is mandatory before suggesting an invasive and costly investigation.

How is Unexplained Weight Loss Treated?

Mostly weight loss is noticed in old age due to underlying systemic disease. Once the underlying cause is identified, patients are treated as per the primary cause. If no other cause is identified despite extensive tests, the person should consult their dietician for proper diet. A high-protein diet along with nutritional supplements are suggested in such cases. Social or emotional factors should not be ignored, and individuals should be provided adequate counseling by their counselors.


Depression may cause unexplained weight loss. Sometimes a hectic schedule or lifestyle can also affect our eating habits which cause poor dietary intake and unexplained weight loss. Misuse of alcohol and drug can also lead to unexplained weight loss, as alcoholic patients lose weight due to self-neglect. Therefore, excessive alcohol use should always be avoided. Loss of more than 5 % of body weight mandates consultation with your physician. In the event of a lack of medical causes, minor stresses and setbacks may cause weight loss, which can easily be remedied through self-love.

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Dr. Muhammad Zubayer Alam
Dr. Muhammad Zubayer Alam

Pulmonology (Asthma Doctors)


weight loss
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