Why insulin resistance can develop long before blood sugar becomes abnormal, and what your blood tests may be missing.
When we think about metabolic health, blood glucose is often the first measurement that comes to mind.
It's routinely checked in blood tests, monitored by people with diabetes and widely regarded as an indicator of how well the body is managing carbohydrates.
But there's an important distinction that's often overlooked.
A normal blood glucose result tells us how much glucose is circulating in your bloodstream. It doesn't necessarily tell us how much effort your body is making to keep it there.
And understanding that difference could change the way you think about your health.
Your body is remarkably good at compensating
Our bodies are designed to maintain blood glucose within a relatively narrow range.
When we eat, carbohydrates are broken down into glucose, which enters the bloodstream. The pancreas responds by releasing insulin, a hormone that helps our cells take up glucose and use or store it for energy.
In a metabolically healthy person, this process is efficient. Insulin rises appropriately after a meal, glucose is managed and insulin levels gradually return towards baseline.
But what happens when our cells become less responsive to insulin?
The pancreas may compensate by producing more.
Initially, this can be remarkably effective. Blood glucose remains within the normal range, even though the body is requiring greater amounts of insulin to achieve that result.
This is one reason insulin resistance can develop long before routine glucose testing reveals a problem.
It's not necessarily that the system has stopped working.
It's that the system is having to work harder.
Why elevated insulin matters
Insulin does far more than regulate blood glucose.
It also plays a central role in energy storage, fat metabolism and the regulation of fuel availability.
After eating, insulin helps direct nutrients into storage and suppresses the release of fatty acids from fat tissue. As insulin falls between meals, the body can increasingly access stored energy.
This is a normal and essential process.
However, when insulin resistance develops, fasting and post-meal insulin levels may become persistently elevated.
Higher insulin levels can make it more difficult to mobilise stored fat while insulin remains elevated. Insulin resistance is also closely associated with increased abdominal fat, fatty liver and disturbances in blood lipids.
Importantly, insulin isn't the sole cause of weight gain or visceral fat accumulation. Overall energy balance, genetics, physical activity, sleep, hormones and other metabolic factors all contribute.
But insulin sensitivity is a critical part of the picture.
The goal isn't to eliminate insulin or prevent its normal rise after meals.
It's to help your body respond efficiently so that it doesn't need to produce excessive amounts to do its job.
The metabolic changes that can precede type 2 diabetes
Type 2 diabetes generally develops over time, rather than appearing without warning.
For many people, the process involves a gradual deterioration in insulin sensitivity, followed by increasing demands on the pancreas.
During this period, other metabolic changes may also emerge:
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Increasing waist circumference and visceral fat
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Elevated fasting insulin
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Rising triglycerides
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Reduced HDL cholesterol
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Fat accumulation in the liver
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Increasing blood pressure
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Changes in body composition, including reduced muscle mass
Not everyone experiences these changes in the same order, and some people develop insulin resistance without obvious symptoms or excess body weight.
That's why relying on appearance, weight or one blood test can be misleading.
Five markers worth understanding
Rather than searching for one perfect measurement, I encourage people to consider several aspects of their metabolic health.
1. Fasting insulin
Fasting insulin measures the amount of insulin circulating after an overnight fast.
Higher levels can suggest that the body is compensating for reduced insulin sensitivity, particularly when interpreted alongside fasting glucose.
However, fasting insulin testing isn't routinely recommended for diagnosing insulin resistance, and there is no universally accepted diagnostic cut-off. Results can vary between laboratories and need clinical interpretation.
It can provide additional context in selected situations, but it shouldn't replace established diabetes screening tests.
2. HbA1c and fasting glucose
Fasting glucose provides a snapshot of blood glucose at the time of testing.
HbA1c reflects average glucose exposure over approximately the previous two to three months.
Both are valuable for screening and diagnosing diabetes and prediabetes.
However, neither directly measures insulin sensitivity. Glucose can remain within the reference range during earlier stages of insulin resistance.
This is why a normal result is reassuring, but doesn't necessarily provide a complete assessment of metabolic health.
3. Triglycerides and HDL cholesterol
These two blood lipid markers can offer useful clues about metabolic function.
Higher triglycerides and lower HDL cholesterol are commonly associated with insulin resistance and metabolic syndrome.
The relationship between the two can be informative, although their ratio isn't a standalone diagnostic test.
It's also important to assess LDL cholesterol and, where appropriate, ApoB and other cardiovascular risk factors rather than focusing exclusively on triglycerides and HDL. (see our Comprehenisve Cardiovasular Pathology test)
4. Waist circumference and visceral fat
The location of body fat matters.
Visceral fat is stored deep within the abdomen, surrounding internal organs. Excess visceral fat is associated with insulin resistance, inflammation, fatty liver and increased cardiometabolic risk.
A practical screening tool is your waist-to-height ratio.
As a general guide, aim to keep your waist circumference below half your height.
For someone who is 170cm tall, that means a waist measurement below approximately 85cm.
This isn't a direct measurement of visceral fat, but it can help identify abdominal fat-related risk.
5. Muscle mass and body composition
Muscle is one of our most important metabolic tissues.
It plays a major role in glucose disposal, particularly after meals, and regular muscle contraction can stimulate glucose uptake through mechanisms that don't rely entirely on insulin.
From around the age of 30, muscle mass and strength can gradually decline, particularly if we become less active.
Maintaining muscle through progressive strength training and adequate protein intake helps support insulin sensitivity, metabolic function and healthy ageing.
This is why two people with identical body weights may have very different metabolic profiles.
What can you do to improve insulin sensitivity?
The encouraging news is that insulin sensitivity is influenced by several modifiable lifestyle factors.
And you don't necessarily need to make dramatic changes to see benefits.
Build muscle. Aim for progressive strength training three times each week. Muscle provides an important site for glucose uptake and storage.
Move after meals. A 10 to 20-minute walk after dinner can help reduce the post-meal glucose rise by encouraging working muscles to use circulating glucose.
Prioritise protein and fibre. Build meals around quality protein, colourful vegetables, healthy fats and fibre-rich whole foods. These support satiety, muscle maintenance and better overall metabolic health.
Consider your eating pattern. If you're constantly grazing, consider whether your meals are sufficiently satisfying. Allowing comfortable breaks between meals may help reduce unnecessary eating occasions, although meal frequency alone doesn't determine fat loss or insulin resistance.
Be strategic with sweet foods. If you're enjoying something sweet, having it immediately after a balanced meal rather than on an empty stomach may moderate the glucose response. Portion size and total dietary intake still matter.
Protect your sleep. Inadequate or disrupted sleep can reduce insulin sensitivity, increase hunger and make appetite regulation more difficult.
Address abdominal fat where appropriate. Reducing excess visceral fat can improve insulin sensitivity and several other metabolic risk markers, even when overall weight loss is relatively modest.
These strategies work together. There isn't one supplement, food or exercise that can replace the benefits of consistently improving your overall lifestyle.
Why prevention needs to begin earlier
One of the challenges with metabolic dysfunction is that it can remain largely silent.
You may feel reasonably well. Your weight might be stable. Your fasting glucose could be normal.
Yet other aspects of metabolic health may already be changing.
This doesn't mean everyone needs extensive pathology testing or should be worried about every result.
It means we should be more curious about the broader picture, particularly if there's a family history of type 2 diabetes, increasing abdominal fat, high blood pressure, abnormal lipids or other metabolic risk factors.
Discussing appropriate screening with your healthcare professional can help identify which measurements are relevant to you.
At Inside Health, our philosophy is built around understanding what's happening beneath the surface, rather than focusing exclusively on body weight or symptoms.
Because the earlier we recognise changes in metabolic health, the more opportunity we have to address them through nutrition, movement, strength training, sleep and other sustainable lifestyle strategies.
The bigger picture
A normal blood glucose result is good news.
But it isn't the complete story.
Metabolic health involves how efficiently we process and store nutrients, respond to insulin, maintain muscle, regulate blood lipids and manage energy.
These systems are interconnected, and meaningful improvements often begin well before we see dramatic changes in body weight or blood glucose.
The real question isn't simply whether your blood glucose is normal. It's whether your metabolism is functioning efficiently enough to keep you healthy for years to come.
And that's why looking beyond a single number matters.
Inside Health provides evidence-informed nutrition, metabolic health education, body composition support and pathology insights to help you better understand your health from the inside out.
This article is general educational information and is not a substitute for individual medical advice.
