Why insulin
Your blood test says you’re fine. Your insulin might disagree.
Glucose is the number everyone checks, and it is the last one to change. This is the story it does not tell you.
A familiar story
- 1
The check-up
“Your bloods look fine.”
You are in your late thirties. You feel mostly well. A bit flat after lunch, maybe. Your belt is a notch tighter than it was, but whose isn’t?
Your doctor runs the usual tests. Fasting glucose: 5.2 mmol/L. Normal. You go home reassured, and you have every reason to be. By the standard everyone uses, you are fine.
- 2
What nobody measured
Your pancreas is working overtime.
Insulin is the hormone that moves glucose out of your blood and into your cells. When your muscles, liver and fat cells start to respond to it less well, your body does not let glucose rise. It makes more insulin instead.
That is insulin resistance. Your glucose stays perfect because your insulin is working harder and harder to hold it there. The test you took measures the result of that effort, not the effort itself.
- 3
The quiet years
High insulin does not sit still.
Insulin is a storage signal. Kept high, it favours storing fat, especially around the middle and in the liver. Over the years the other markers start to drift: triglycerides creep up, HDL cholesterol slips down, blood pressure edges higher.
None of it hurts. Each number on its own might still look borderline. Together they are the pattern doctors call metabolic syndrome, and insulin resistance runs through all of it.
- 4
Ten, fifteen, twenty years on
Glucose finally moves.
Eventually the pancreas cannot keep up. Insulin output falls behind, and only then does glucose rise. In the Whitehall II study, fasting glucose climbed sharply only in the last two years or so before a diabetes diagnosis.
The World Health Organization notes that type 2 diabetes is often diagnosed several years after it begins, after complications have already arisen. The glucose test did not warn you. It reported the damage.
The years when change is easiest are exactly the years a glucose test cannot see. Insulin can.
Insulin moves first. Glucose moves last.
Illustration of the typical pattern, not individual data.
Think of glucose as the smoke alarm and insulin as the heat sensor. You want the warning before there is smoke.
What the experts say about insulin.
On measuring insulin once or twice a year:
“As an endocrinologist I couldn’t agree more… that’s the holy grail right there.”
Dr Robert Lustig
Paediatric endocrinologist, University of California, San Francisco
Source: “How to Avoid Insulin Resistance and Why it’s Important”, Levels, with Dr Dom D’Agostino
“Shocking to me in 2022 that not every single person gets this test… We’re checking people’s cholesterol. We’re checking their A1C. Nobody checks insulin.”
Dr Mark Hyman
Family physician and author
Source: “Why Insulin Tests Are Important”, TikTok
“These diseases, as I noted, that we once thought were totally unrelated to each other, do in fact share a common metabolic core, and that core is insulin resistance.”
Prof Ben Bikman
Metabolic scientist, Brigham Young University
Source: mindbodygreen podcast, “How to optimize your metabolism”
“As you move up that curve, you are becoming more and more insulin resistant. That means you need more and more insulin to do the same job.”
Dr Rangan Chatterjee
GP and author
Source: TEDx talk, “How to Make Diseases Disappear”
“The body produces enough insulin to overcome this resistance, so the blood glucose stays relatively normal… Even up to 14 years prior to the diagnosis of type 2 diabetes you get this rising insulin resistance.”
Dr Jason Fung
Nephrologist and author
Source: Low Carb Down Under, “A New Paradigm of Insulin Resistance”
“Insulin resistance related diseases are the number one killers. In the US, they kill every year more people than died of COVID.”
Nina Teicholz
Science journalist and author
Source: Family Health Lab podcast
Quotes are taken from public talks and interviews. None of these people is affiliated with IN5ULIN or endorses it. Photos via Wikimedia Commons: Lustig by Ancestry Foundation, CC BY 4.0; Hyman by Stephanie Williams, CC BY-SA 4.0; Bikman by Ben P L, CC BY-SA 2.0; Chatterjee by Mateusz Malta, CC BY-SA 4.0; Teicholz by Mathew Robinson, CC BY-SA 4.0.
Metabolic syndrome
Five warning signs. One common thread.
Metabolic syndrome is a cluster of risk factors for heart disease and type 2 diabetes that turn up together far more often than chance would explain. Under the harmonised definition agreed by the major international heart and diabetes bodies, having any three of the five markers opposite means you have it.
The thread running through them is insulin resistance. When the World Health Organization first set out a formal definition in 1998, evidence of insulin resistance or abnormal glucose handling was the one required component.
So what’s missing?
Look at the list again. Five markers, and not one of them measures insulin.
Any three of these five
- Waist
- Central obesity, measured by waist size (cut-offs vary by population)
- Triglycerides
- 1.7 mmol/L or higher
- HDL cholesterol
- Below 1.0 mmol/L in men, below 1.3 mmol/L in women
- Blood pressure
- 130/85 mmHg or higher
- Fasting glucose
- 5.6 mmol/L or higher
Or being treated for the condition. Harmonised definition, Alberti et al., Circulation 2009.
Insulin resistance
But are we missing something?
Insulin resistance means your body needs more insulin than it should to keep glucose in range. It is a statement about insulin. Checking for it without an insulin result means working backwards from the side effects.
Without insulin
What we know
Waist, triglycerides, HDL, blood pressure and glucose are downstream signs. They can take years to drift, and each one has other causes. A normal set tells you little. An abnormal set tells you late.
With insulin
What we NEED to know
Fasting insulin alongside fasting glucose gives HOMA-IR, the standard estimate of insulin resistance from one blood sample. Repeat it and you can see which way you are heading.
Where the road leads.
Metabolic syndrome and insulin resistance are linked with some of the most common chronic diseases in the world.
Type 2 diabetes
The best known end point. More than 95% of people with diabetes have type 2.
Heart attack and stroke
Metabolic syndrome is defined as a cluster of risk factors for cardiovascular disease, the world’s leading cause of death.
High blood pressure
One of the five markers, and one that 44% of people who have it do not know about.
Fatty liver disease
Fat building up in the liver (MASLD, formerly NAFLD) is closely tied to insulin resistance.
Polycystic ovary syndrome
Insulin resistance is common in PCOS and high insulin is linked with its hormonal effects.
Obesity
Especially fat carried around the waist, which is itself one of the five markers.
Chronic kidney disease
Diabetes and high blood pressure are leading causes of kidney damage.
Dementia
Research links insulin resistance and type 2 diabetes with a higher risk of cognitive decline.
The scale of the problem.
The World Health Organization’s latest figures.
830 million
people living with diabetes in 2022, up from 200 million in 1990. More than 95% have type 2.
1 in 7
people worldwide, 1.1 billion, were living with obesity in 2024. Adult obesity has more than doubled since 1990.
1.4 billion
adults aged 30–79 had high blood pressure in 2024. 44% of them did not know.
19.8 million
deaths from cardiovascular disease in 2022, about a third of all deaths. The world’s leading cause of death.
Source: World Health Organization fact sheets on diabetes, obesity, hypertension and cardiovascular diseases.
Glucose looks similar. Insulin does not.
Two foods, tested over 90 minutes. Glucose stayed in a similar range for both. Insulin did not: the sugar drove it more than three times higher than the banana did.
240 g banana
48 g table sugar
Illustration based on one person’s finger-prick tests, n=1.
Insulin goes up years before glucose does. Check it first.
IN5ULIN measures insulin from a small blood sample in minutes, so you can see the strain while there is still time to change it.
IN5ULIN is not a diagnostic tool. This page is general information, not medical advice. Sources are listed on the Learn page.