Insulin Resistance: Understand the Root Cause

If you've been told your blood glucose (blood sugar) is "borderline" or that you're "pre-diabetic," you've probably also been given advice about cutting sugar and walking more. That advice isn't wrong. But it barely scratches the surface of what's actually happening in your body, and it rarely explains why your blood glucose is too high; what’s driving this to happen.

You may not have heard the term “insulin resistance”, yet this is the early dysfunction that contributes to blood glucose becoming increasingly elevated over time, above what would be considered optimal.

What Insulin Resistance Actually Is

Insulin is a hormone produced by the pancreas. Think of insulin as a key. Insulin’s key role (pardon the pun) is to “unlock” cells and support glucose to move from the bloodstream into the cells where it can be used for energy, or stored for later (in the liver, muscles or fat tissues). Storing glucose protects the blood vessels and nerve cells from damage.

Insulin’s role includes:

• Regulating blood sugar

• Supporting energy production

• Influencing appetite

• Directing fat storage

• Interacting with reproductive hormones

• Influencing inflammation

Insulin resistance happens when your cells stop responding effectively to insulin's signal. Glucose has a harder time getting into the cells, so it lingers in the blood. Your pancreas responds to the elevated blood sugar by producing even more insulin, trying to force the lock.

For a while, this works, blood sugar remains in a "normal" range because insulin levels are quietly climbing higher and higher in the background trying to regulate the blood glucose. This is why standard fasting glucose tests can look fine for years even while insulin resistance is already well underway.

HbA1c is a blood test that Doctors carry out to see how elevated your blood glucose has been over the preceding three months. This can also be “in-range” despite insulin resistance. Left unaddressed, this cycle can progress toward pre- diabetes, type 2 diabetes, weight gain (particularly around the midsection), fatty liver, hormonal imbalances, and increased cardiovascular risk.

As a Registered Nutritional Therapist, I don't look at insulin resistance as a standalone diagnosis to manage. I look at it as a clue; your body's telling me that something upstream needs attention. Let's look at what that really means.

Why Functional Nutrition Looks Beyond "Eat Less Sugar"

Conventional approaches often treat insulin resistance as a simple math problem: too much sugar in, not enough movement out. Reduce the sugar, increase the exercise, done. In practice, insulin resistance is rarely that one-dimensional. From a functional lens, several interconnected systems typically play a role:

Chronic stress and cortisol. Elevated cortisol, from work stress, poor sleep, overtraining, or unresolved emotional stress, signals the liver to release more glucose into the bloodstream, even when you haven't eaten. Over time, this stress related glucose release asks more and more of your insulin response.

Sleep quality. Just a few nights of poor sleep can measurably reduce insulin sensitivity in otherwise healthy people. Sleep isn't a lifestyle nicety; it's a direct lever on blood sugar regulation. In addition, our food choices when tired can be suboptimal; we’re more likely to crave high sugar, carby, often ultra-processed foods which can exacerbate the problem.

Gut health and inflammation. An imbalanced gut microbiome and increased intestinal permeability can drive low-grade, chronic inflammation in the body. Inflammatory signalling molecules interfere with insulin receptor function, making cells less responsive to insulin's message.

Micronutrient status. Magnesium, chromium, zinc, and vitamin D all play important roles in glucose metabolism and insulin signalling. Deficiencies in these nutrients, more common than most people realise, can quietly undermine insulin sensitivity.

Meal timing and composition. It's not just what you eat, but how you eat it. Large, carbohydrate-laden meals eaten in isolation e.g. without protein, fat, or fibre, create sharper blood glucose spikes, which demand a bigger and longer insulin response. Insulin sensitivity is poorer in the evening and overnight.

Movement patterns. Muscle tissue is one of the primary sites where glucose gets stored and utilised. Sedentary lifestyles mean less glucose uptake by the muscles, which leaves more glucose circulating and more work for insulin to do.

Hormone patterns. Insulin resistance often increases as oestrogen levels fall in perimenopause and into menopause and this can be exacerbated by associated increased inflammation and reduced muscle mass, also associated with menopause.

Women with PMOS (Polyendocrine Metabolic Ovarian Syndrome (previously PCOS)) have increased incidence of insulin resistance due to altered hormone related insulin signalling in muscle, liver and fat cells, meaning glucose is not handled as efficiently.

These example explain why two people can eat similar diets and have very different insulin responses.

A Functional Approach to Supporting Insulin Sensitivity

The aim is to identify insulin resistance early. This allows us to identify and address the specific drivers at play for that person. There are however foundational strategies that tend to help most people move in the right direction.

1. Build Meals Around Protein, Fat, and Fibre First

Anchoring meals with protein and healthy fats slows gastric emptying and blunts the glucose spike that would otherwise come from eating carbohydrates alone. Adding fibre-rich vegetables can also slow glucose absorption. A practical approach is to fill half your plate with above ground, non-starchy vegetables, a quarter with a protein source, and the remaining quarter with a smart carbohydrate choice. Avoiding highly refined, processed carbohydrates including cakes and biscuits really helps reduce insulin secretion.

2. Mind the Order and Pairing of Foods

Research on meal sequencing suggests that eating low carb vegetables (grown above ground and salads) and protein before carbohydrates (rather than starting with bread, starchy carbs like potatoes or rice) can meaningfully reduce the resulting blood sugar spike, even when the same meal but different sequence is eaten.

3. Move After Eating

A short walk, even 10 minutes, after a meal helps working muscles pull glucose out of the bloodstream, easing the burden on insulin. This is a small habit with a big benefit. If you can’t get out, using big muscles like the thighs and buttocks can do the same thing e.g. walking upstairs, squats or lunges.

4. Prioritise Sleep as a Metabolic Intervention

Aiming for consistent, quality sleep isn't just about feeling rested. It's one of the more direct ways to support next-day insulin sensitivity and support better food choices.

5. Address Stress Directly

Since cortisol and insulin are so closely linked, chronic stress management is key. Life is stressful so find ways to notice when you feel stressed so you can take action to bring some calm back. Breathwork, time in nature, relaxation techniques or mindfulness, or simply protecting downtime, is a legitimate part of a metabolic health plan, not an afterthought.

6. Support Gut Health

Eating a range of colourful fibre-rich plant foods and fermented foods (like yoghurt, kefir, kombucha and cheese) can support a more balanced microbiome, which in turn may help reduce the inflammatory load that interferes with insulin signalling. Aiming for 30g of fibre a day is ideal but rarely achieved by the majority of adults. Generically therefore, over 90% of people would benefit from eating more fibre rich foods, but go slow if increasing and drink extra fluids to support gut transit.

7. Check Key Nutrient Levels

Working with a practitioner to assess magnesium, vitamin D, and other relevant markers can uncover deficiencies that are quietly working against insulin sensitivity. Diet alone may not fully correct for a while so testing can also support targeted supplementation to create a nutritional bridge until dietary changes are in place.

The Bigger Picture

Insulin resistance isn't a failing or simply the result of "too much sugar." It's a downstream expression of multiple systems like sleep, stress, gut health, nutrient status, daily movement and genes, all interacting together.

That's actually good news; it means there are many different options for improvement, and progress in one area (better sleep, for example) often supports the others e.g. stress or better food choices, or more energy in order to move or exercise more.

If you're navigating insulin resistance, the goal isn't perfection, it's identifying which of these levers matters most for your body and building sustainable habits around them. Personalised functional nutritional therapy can guide effective and sustainable health plans that can support insulin sensitivity at it's root cause.