Obesity

Obesity means having excess body fat that raises the risk of health problems. In adults it is usually screened for with body mass index (BMI): a BMI of 30 or more is classed as obesity, and lower thresholds are often used for some Asian populations. BMI doesn't measure body fat directly, so waist size and overall health are also considered. Obesity raises the risk of type 2 diabetes, high blood pressure, fatty liver disease, sleep apnea, joint problems, some cancers and heart disease. Genetics, environment, sleep, medicines and other medical conditions all play a part.

Lab tests linked to obesity:

• HOMA-IR: an estimate of insulin resistance, which is common with obesity.
• C-reactive protein (CRP): often mildly raised, reflecting low-grade inflammation.
• Estradiol (male) and estrogens, total (male): can be higher in men with obesity, because fat tissue converts testosterone to estrogen.
• Free testosterone, direct (male): often lower in men with obesity. It frequently improves with weight loss.
• Doctors may also order HbA1c or fasting glucose, a lipid panel, liver enzymes, TSH and kidney function.

How results are read:

• These tests look for complications and related conditions. No blood test diagnoses obesity.
• A mildly raised CRP is common with obesity, so a high CRP needs other causes ruled out before it is put down to weight.
• Low testosterone in men with obesity is often functional and can improve with weight loss. Other causes are still considered.
• An underactive thyroid is a less common cause of weight gain, so TSH is often checked.

When to see a doctor:

• See a doctor about support with weight, and about checks for diabetes, blood pressure, cholesterol and liver health.
• See a doctor about loud snoring with pauses in breathing or daytime sleepiness, which can signal sleep apnea.

Clinical takeaway: obesity is assessed with BMI and waist size, and blood tests look for the metabolic and hormonal changes that often come with it.