Unexplained Weight Loss: When to Worry

The practical threshold doctors use is this: losing more than five per cent of your body weight over six to twelve months, without trying, deserves assessment. For a 70 kg adult that is around 3.5 kg; for a 90 kg adult, about 4.5 kg. Below that, with no other symptoms, it is usually explained by ordinary changes in appetite, stress or activity.

Above it, the right response is an appointment within weeks rather than months. Not because the cause is usually sinister, but because most of the causes that are found are considerably easier to treat when caught early.

Why weight falls without you trying#

Body weight is a balance between what you take in and what you burn. Unintentional loss means one of three things has shifted: you are eating less than you realize, you are absorbing less of what you eat, or your body is burning more than usual.

That framing is useful because it maps directly onto the causes. Depression, pain, nausea and poorly fitting dentures reduce intake. Celiac disease, inflammatory bowel disease and pancreatic problems reduce absorption. Thyroid overactivity, uncontrolled diabetes, chronic infection and cancer raise consumption.

The causes in rough order of frequency#

An overactive thyroid, with tremor, heat intolerance, palpitations and anxiety. Diabetes that is new or poorly controlled, with thirst, frequent urination and fatigue. Depression and anxiety, which reliably suppress appetite and are among the most common causes of all. Celiac disease and other gut conditions, with bloating, diarrhea or iron deficiency.

Chronic infection matters greatly depending on where you live: tuberculosis remains a leading global cause of weight loss with night sweats and cough, and HIV should be considered. Chronic heart, lung, kidney and liver disease all cause weight loss at later stages. Medicines, and alcohol, are frequently overlooked.

Cancer is on the list and is the reason the threshold exists. It is not the most likely explanation, but it is the reason not to wait and watch for a year.

What makes it more urgent#

Weight loss traveling with difficulty swallowing, persistent vomiting, blood in stool or black stools, a new lump anywhere, jaundice, drenching night sweats, or a cough lasting more than two or three weeks. Any of these combinations should prompt an appointment within days.

What to bring to the appointment#

Two numbers and a list: your current weight, a previous documented weight with its date, and a list of every medicine and supplement you take. Add a note of appetite, mood, bowel habit, and any symptom you have dismissed as unrelated. That short preparation usually determines whether the right tests are ordered at the first visit rather than the second.

The wider picture#

Weight change is one of the clearest signals that a routine check is overdue, and the fuller guide to health checkups by age sets out what is worth screening for, and when.