Wellness . Symptoms guide
Unexplained Weight Gain: Hormone and Metabolic Testing
Quick answer
Persistent unexplained weight gain without a change in diet or activity deserves a metabolic and hormonal review. Thyroid dysfunction, insulin resistance, PCOS in women and falling testosterone in men are among the common medical drivers. Bloodwork is a useful first step to identify them. Note: UK clinical guidelines (NICE NG12) define a clinically significant unexplained weight CHANGE threshold (5 percent in 6 to 12 months) for unintentional weight LOSS, not gain; for weight gain, the trigger for investigation is the absence of a behavioural explanation rather than a fixed percentage.
This patient information is being clinically reviewed by our team. The factual content aligns with UK diagnostic frameworks, drawing on NHS primary care pathways, NICE guidelines on type 2 diabetes and thyroid dysfunction, and clinical guidance from the Society for Endocrinology.
What this might be
- Hypothyroidism. Slows metabolism; often the first thing to test.
- Insulin resistance and pre-diabetes. HbA1c is the NICE-endorsed first-line marker for dysglycaemia; fasting insulin and HOMA-IR add specificity for insulin resistance itself.
- PMOS (formerly PCOS). Polyendocrine Metabolic Ovarian Syndrome is a major hormonal driver of unexplained weight gain in women. While frequently accompanied by elevated male hormones, it is the underlying insulin resistance that primarily disrupts glucose disposal and alters fat storage, occurring even in non-androgenic phenotypes.
- Cushing's syndrome (rare). Characterised by a severe, sustained overproduction of cortisol. Because cortisol levels naturally peak and drop throughout the day, a standard random blood test cannot diagnose or rule this out; definitive screening requires specialised investigations, such as a low-dose dexamethasone suppression test or a 24-hour urinary free cortisol collection, arranged under specialist guidance.
- Medication effects. Antidepressants, antipsychotics, steroids, beta blockers.
Common features that suggest this
- Unexplained weight gain occurring over weeks or months despite a completely stable nutritional and physical activity baseline.
- Changes in fat redistribution, such as an isolated increase in central abdominal tissue or a rounded fullness appearing around the face and neck.
- Concurrent physiological changes, including severe fatigue, pronounced cold intolerance, proximal muscle weakness, or new skin tags and dark skin patches.
Recommended tests
Same-day appointments at our Harley Street clinic, results clinician-reviewed.
Need a marker not in these panels? Build a custom panel and a GMC-registered clinician will design one for you.
Markers your clinician will commonly look at
These are the individual blood markers in the recommended panels above. Click any to read what it measures, its UK reference range, and what high or low values mean.
Testing advice
Fasting is recommended for the General Wellness panel (glucose, HbA1c, cholesterol). Morning slot helpful if hormones included.
Common questions
Will testing diagnose the cause?
It rules out key medical barriers like thyroid dysfunction or insulin resistance. If your results are normal, that's highly valuable clarity: it eliminates these conditions so you and your doctor can focus on lifestyle, sleep, stress, or medications.