What is insulin resistance, and what are the signs?
Insulin resistance usually causes no symptoms you can feel, which is why it is found through blood tests rather than how you seem. The visible clues are subtle — and it rarely travels alone.
Insulin is a hormone made by the pancreas, and insulin resistance means the cells in the muscle, fat and liver do not respond to it well and cannot easily take up glucose from the blood [s1]. To keep blood sugar in range, the pancreas makes more insulin; insulin resistance can lead to raised blood glucose levels and weight gain [s1]. So the first and most important answer to "what are the signs" is deflating: people who have insulin resistance and prediabetes usually have no symptoms at all [s1]. It is largely a silent state, which is why it is usually caught on a blood test rather than noticed in a mirror.
The signs that do sometimes show
When there is anything visible, it tends to be on the skin. Some people with prediabetes have darkened skin in the armpit or on the back and sides of the neck, and they may also have many small skin growths in those same areas [s2]. Those patches — clinicians call the darkening acanthosis nigricans — are among the few outward hints that insulin has been running high, but their absence proves nothing, because most people with the condition have no sign at all [s1].
The symptoms people often attribute to insulin resistance — fatigue, cravings, brain fog — are not part of any established sign list for it [s1]. That does not mean nothing is happening; it means those feelings are not a reliable way to tell whether insulin resistance is present.
How it is actually measured
Because you cannot feel it, insulin resistance is defined by numbers. In everyday care the relevant tests are the ones used to catch prediabetes: an A1C result between 5.7 and 6.4 percent, or a fasting plasma glucose between 100 and 125 mg/dL, puts a person in the prediabetes range [s1]. Those tests measure glucose, the downstream consequence, rather than resistance itself. They also mark a trajectory rather than a fixed state: if blood glucose levels keep going up, prediabetes can progress to type 2 diabetes [s1], which is part of why the silent, symptomless phase is the one worth catching.
Researchers estimate the resistance more directly. The homeostasis model assessment, or HOMA, introduced in 1985, calculates insulin resistance and beta-cell function from a single pair of fasting plasma glucose and insulin measurements [s4]. HOMA is a research and epidemiological tool, not a routine clinical verdict, but it is the reason so many studies can put a number on "insulin resistance" at all [s4].
It rarely travels alone
The clinically useful framing is that insulin resistance sits at the centre of a cluster. A group of risk factors for cardiovascular disease and type 2 diabetes occur together more often than chance allows, and are known as the metabolic syndrome: raised blood pressure, dyslipidaemia (raised triglycerides and lowered HDL cholesterol), raised fasting glucose, and central obesity [s3]. Under the 2009 harmonised definition agreed by several major organisations, three abnormal findings out of those five qualify a person for the metabolic syndrome, and waist measurement is kept as a useful preliminary screening tool [s3]. So the practical "sign" of insulin resistance is often not one thing but a pattern — a rising waist, blood pressure and glucose creeping up together.
Who is more likely to have it, and how common it is
The risk factors NIDDK lists are familiar: having overweight, obesity or a large waist size; being age 35 or older; and having a family history of diabetes [s1]. And the state is not rare. About 1 out of every 3 adults has prediabetes, the condition insulin resistance most often produces [s2].
What this means for a reader
Two things follow. First, you cannot rule insulin resistance in or out by how you feel, so waiting for a symptom is the wrong strategy — the darkened-skin sign appears in only some people, and most have none [s1][s2]. Second, if you have the risk factors, the way to know is a blood test, and the figures that matter are the glucose thresholds a clinician can order and interpret [s1]. This is information, not a diagnosis or a treatment plan: whether and how to test, and what to do about a result, is a conversation to have with a clinician who can see the whole picture.
Sources
- Insulin Resistance & Prediabetes — National Institute of Diabetes and Digestive and Kidney Diseases
- Prediabetes — MedlinePlus, National Library of Medicine
- Harmonizing the Metabolic Syndrome — Circulation, 2009
- Homeostasis model assessment: insulin resistance and beta-cell function from fasting plasma glucose and insulin concentrations in man — Diabetologia, 1985
Sources
- Insulin Resistance & Prediabetes — National Institute of Diabetes and Digestive and Kidney Diseases
- Prediabetes — MedlinePlus, National Library of Medicine
- Harmonizing the Metabolic Syndrome — Circulation , October 20, 2009
- Homeostasis model assessment: insulin resistance and beta-cell function from fasting plasma glucose and insulin concentrations in man — Diabetologia , July 1, 1985
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