Unexplained Weight Loss: When to Worry and What to Do

26 Sep 2025

Most people expect weight loss to follow changes in diet or exercise. But if the pounds are dropping off without you trying, it can be a cause for concern. Unexplained weight loss, generally defined as losing more than 5% of your body weight in six to twelve months without effort, may signal an underlying health issue.

Here’s what you need to know about possible causes, when to seek help, and the steps to take.

Common Non-Serious Reasons

Not all unintentional weight loss is linked to serious illness. Sometimes it’s due to:

• Increased physical activity without adjusting food intake
• Stress or anxiety affecting appetite
• Minor infections that temporarily reduce eating
• Age-related changes in appetite or muscle mass

However, persistent or significant weight loss should not be ignored.

Medical Causes to Be Aware of

A range of health conditions can contribute to unexplained weight loss, including:

• Thyroid disorders – An overactive thyroid can speed up metabolism and cause weight loss.
• Diabetes – Uncontrolled blood sugar may lead to sudden weight changes.
• Digestive conditions – Problems like coeliac disease, inflammatory bowel disease, or chronic infections can reduce nutrient absorption.
• Cancer – In some cases, unexplained weight loss can be an early warning sign.
• Depression or mental health conditions – Loss of appetite is a common symptom.

If you’re concerned, booking a Private GP Appointment is the safest first step.

When to See a Doctor

Seek medical advice promptly if your weight loss is:

• More than 5% of your body weight within six months
• Accompanied by fatigue, night sweats, or fever
• Linked to changes in bowel habits or abdominal pain
• Associated with loss of appetite or difficulty swallowing

What Tests Might be Recommended

To investigate unexplained weight loss, a GP may suggest:

• Blood tests – To check thyroid function, diabetes, infection, or vitamin levels
• Stool tests – To look for signs of inflammation or infection
• Imaging scans – If more detailed investigation is needed
• Specialist referrals – Depending on symptoms and test results

At South Kensington Medical & Dental, we offer Comprehensive Health Screening and targeted Blood Tests to help identify underlying causes.

Taking Action Early

The cause of unexplained weight loss is not always serious, but identifying the reason early can make a big difference. Even if tests show no major condition, having reassurance and guidance on improving nutrition and lifestyle is valuable.

Final Thoughts

Weight loss without trying can feel unsettling. While it sometimes results from stress or minor illness, it can also be the body’s way of signalling something more significant.

If you’ve noticed unintentional weight loss, don’t wait to see if it improves on its own — arranging a medical review can provide clarity and peace of mind.