Losing 5% or more of body weight over 6–12 months without intentional dieting is clinically significant and warrants a full medical evaluation.
Unintentional weight loss — losing weight without deliberately trying — is one of medicine's most important red-flag symptoms. While gradual weight loss over months can be missed by patients, losing more than 5% of body weight within 6–12 months is clinically significant and should always trigger investigation. In Korea, where access to diagnostic tests and specialist care is excellent, early investigation of unexplained weight loss leads to earlier diagnosis and better outcomes.
The causes fall into several categories. Malignancy (cancer) is one of the most feared causes — cancers of the stomach (notably common in Korea), oesophagus, pancreas, lung, lymphoma, and leukaemia frequently present with weight loss as an early symptom. Endocrine causes include hyperthyroidism (overactive thyroid accelerating metabolism) and poorly controlled diabetes (glucose wasting in urine). Gastrointestinal causes include coeliac disease, inflammatory bowel disease, and chronic pancreatitis. Psychiatric causes — particularly depression, anxiety, and eating disorders — are common. Infections including HIV and tuberculosis (TB) are also important to exclude.
Investigation begins with a thorough history and examination, followed by targeted blood tests: full blood count, inflammatory markers (ESR, CRP), thyroid function, liver and renal function, HIV test, and tumour markers if indicated. Chest X-ray, abdominal ultrasound, and — given Korea's high stomach cancer rate — upper endoscopy are common initial investigations. Korea's community health centres and private GPs provide excellent initial work-up, with prompt referral to oncology, endocrinology, or gastroenterology as needed.
Key Points
- 5% body weight loss without trying over 6–12 months = red flag
- Always investigate — cancer, diabetes, thyroid disease must be excluded
- Blood tests, chest X-ray, and endoscopy/ultrasound are standard first-line investigations
- Psychiatric causes (depression, eating disorders) are also common
- Korea's National Cancer Center provides oncology investigation and treatment
- Early diagnosis dramatically improves cancer outcomes
Causes & Risk Factors
- Malignancy — cancer is a key diagnosis to exclude, including stomach cancer
- Hyperthyroidism — excess thyroid hormone accelerates metabolism
- Poorly controlled diabetes — glucose lost in urine
- Depression — reduced appetite and motivation
- Coeliac disease — malabsorption from gluten-triggered gut damage
- HIV, tuberculosis — chronic infection with metabolic drain
When to See a Doctor
- Lost more than 3–5 kg without trying over 2–3 months
- Weight loss with night sweats, fever, or fatigue
- Weight loss with change in bowel habits, blood in stool, or indigestion
- Weight loss with persistent cough, haemoptysis (coughing blood)
- Any unintentional weight loss should be discussed with a doctor
For emergencies in Korea, call 119
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This content is published for educational purposes only. For accurate diagnosis and personalised treatment, consult a licensed KMA physician in Korea.
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Medical Disclaimer
This article is published by DoctorsInKorea.com for educational and informational purposes only. It does not replace a professional clinical evaluation by a licensed healthcare provider. For accurate medical diagnosis and personalised treatment paths, please book an appointment with a licensed KMA physician. For immediate life-threatening medical emergencies in Korea, please call 119.
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Last reviewed: March 1, 2025