Insulin resistance, weight and blood tests

Insulin resistance is one of the most searched health terms connected with weight, and one of the most loosely used. Here is what it means, how it connects to prediabetes and type 2 diabetes, which blood tests doctors use, and why one number on a lab report rarely settles anything.

What insulin resistance is, in plain words

Insulin is a hormone made by the pancreas. It helps the body use glucose, the sugar in your blood, for energy. In insulin resistance, cells in the muscles, fat and liver do not respond to insulin as well as they should. According to the US National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), over time the pancreas may then not make enough insulin to help the extra glucose into the cells, and blood glucose rises.

Insulin resistance is more a description of how the body is working than a diagnosis with its own standard blood test. NIDDK says health care professionals may not test for it, and the test is mainly used in research.

How it relates to weight

The link runs both ways. Overweight, obesity and a large waist make insulin resistance more likely, and NIDDK notes that insulin resistance itself can lead to higher blood glucose and weight gain. The American Diabetes Association (ADA) links prediabetes with obesity, especially abdominal obesity.

Weight is not the only factor. NIDDK also lists age 35 or older, diabetes in the family, inactivity, smoking, diabetes in a past pregnancy, conditions such as polycystic ovary syndrome or sleep apnoea, and long-term use of certain medicines. What causes insulin resistance is still not fully understood.

From insulin resistance to prediabetes and type 2 diabetes

Prediabetes means blood glucose higher than normal but not high enough for type 2 diabetes. If it keeps rising, type 2 diabetes can follow: NIDDK says people with prediabetes have a high chance of developing it within 5 to 10 years, though not everyone does.

Symptoms: usually none

This is why insulin resistance is easy to miss. NIDDK states that people with insulin resistance and prediabetes usually have no symptoms. The NHS says most people with type 2 diabetes itself do not have the typical symptoms, such as feeling very tired, peeing more or losing weight without trying.

One visible sign is sometimes mentioned: acanthosis nigricans, darker and velvety skin in body folds such as the neck or armpits. MedlinePlus lists the hormone changes of diabetes and obesity, often called insulin resistance, among its causes. It has other causes too: a reason to see a doctor, not a diagnosis.

Which blood tests doctors use

Fasting glucose shows your blood glucose at the moment of the test. HbA1c shows the average over roughly the past three months, and NIDDK adds that it may miss prediabetes in some health conditions. The oral glucose tolerance test measures glucose two hours after a sugary drink. It takes longer and costs more, so it is used less often. Because blood fats can also rise with insulin resistance, cholesterol and triglycerides are often checked too.

HOMA-IR: why there is no single "normal" number

HOMA-IR is not measured directly. It is calculated from fasting glucose and fasting insulin, using a model published in 1985 whose authors noted that the estimate's low precision limits its use. A 2004 review by the same Oxford group calls it valuable when used appropriately, for example in cohort and epidemiological studies, and only with careful interpretation.

There is also no universally agreed threshold. A 2013 study of 2,459 adults in Spain describes great variability in the HOMA-IR cut-offs in use; in its own data the cut-off shifted with the method used to set it, and with age in women without diabetes. Anyone who says a HOMA-IR above a certain number means insulin resistance is claiming something the research has not settled.

The official thresholds, and how doctors use them

Unlike insulin resistance, prediabetes and diabetes have formal diagnostic criteria, from the World Health Organization (WHO) and the ADA, and the two do not fully agree. They describe how doctors make a diagnosis. They are not a tool for diagnosing yourself.

Two points matter more than the numbers. The WHO notes that an HbA1c below 6.5% does not exclude diabetes found by glucose tests, and that fasting glucose alone misses about 30% of previously undiagnosed diabetes. And the ADA requires a diagnosis to be confirmed unless high blood glucose is unequivocal. One borderline result decides nothing.

What generally helps, at the level of the population

The WHO calls lifestyle changes the best way to prevent or delay type 2 diabetes: a healthy body weight, at least 150 minutes of moderate physical activity a week, a diet that limits sugar and saturated fat, and not smoking. NIDDK's list for insulin resistance and prediabetes is similar and adds enough sleep.

Why interpretation belongs with a doctor

The reasons are concrete: the two sets of criteria differ, a single result needs confirming, HbA1c can mislead in some conditions, and HOMA-IR has no agreed cut-off. None of these numbers knows your weight history, your waist, your other results or your medicines.

That is why on a.clinic your doctor reads your blood results, with your questionnaire, before the consultation. Blood glucose is among the tests they need anyway, and if they need more, they will tell you. Any laboratory or your GP can do them.

a.clinic is a technology platform. Healthcare is provided by a licensed doctor, who decides whether any treatment is appropriate for you. We do not decide about specific medicines and do not write about them.

What are the symptoms of insulin resistance?

Usually none, according to NIDDK. Darker, velvety skin in body folds (acanthosis nigricans) can be linked to it, but has other causes too. Blood tests and a doctor tell you more.

What HOMA-IR value is normal?

There is no universally agreed cut-off. Studies report different thresholds depending on population, age, sex and method. Your doctor reads the value alongside your other results.

Can I tell from my results whether I have prediabetes?

The WHO and ADA thresholds describe how doctors diagnose, they differ from each other, and a diagnosis needs confirmation. Treat your results as a reason to talk to a doctor, not as a diagnosis.

How is insulin resistance connected to losing weight?

NIDDK says insulin resistance can contribute to weight gain, and that managing weight, physical activity, healthy food and enough sleep may help prevent or reverse it. What suits you is for a doctor to judge.

Which tests should I have before a consultation on a.clinic?

A body composition scan and blood work, including blood sugar, kidney and liver markers and thyroid function. If your doctor needs anything else, they will tell you.

Sources

• WHO, Diabetes (fact sheet, 2024)
• WHO/IDF, Definition and diagnosis of diabetes mellitus and intermediate hyperglycaemia (2006)
• WHO, Use of glycated haemoglobin (HbA1c) in diagnosis of diabetes mellitus (2011)
• American Diabetes Association, 2. Diagnosis and Classification of Diabetes: Standards of Care in Diabetes 2026
• NIDDK, Insulin Resistance & Prediabetes
• NIDDK, Diabetes Prevention Program (DPP)
• NHS, Type 2 diabetes: symptoms and diagnosis
• MedlinePlus, Acanthosis nigricans
• Matthews et al., Homeostasis model assessment, Diabetologia 1985
• Wallace, Levy, Matthews, Use and abuse of HOMA modeling, Diabetes Care 2004
• Gayoso-Diz et al., Insulin resistance (HOMA-IR) cut-off values and the metabolic syndrome in a general adult population, BMC Endocrine Disorders 2013