Insulin Resistance and Type 2 Diabetes Explained

Insulin resistance and type 2 diabetes are closely linked conditions affecting millions of people in the UK. Insulin resistance occurs when the body's cells stop responding properly to insulin, forcing the pancreas to produce ever-greater amounts to maintain normal blood glucose. Left unaddressed, this can progress through prediabetes to a full diagnosis of type 2 diabetes. Understanding the causes, how the NHS diagnoses and manages the condition, and what steps can reduce long-term risk empowers people to take meaningful action at every stage of the journey.

What is insulin resistance and how does it lead to type 2 diabetes?

Insulin resistance develops when cells in the muscles, liver and fat tissue respond poorly to insulin, prompting the pancreas to produce more until it eventually cannot compensate, causing blood glucose to rise and type 2 diabetes to develop.

Insulin resistance is a condition in which the body's cells respond poorly to insulin, the hormone produced by the pancreas that allows glucose to enter cells and be used for energy. When cells in the muscles, liver and fat tissue become less sensitive to insulin's signal, the pancreas compensates by producing more of it. Over time, this compensatory mechanism can fail, blood glucose levels rise persistently, and type 2 diabetes develops.

Insulin itself is released by beta cells in the pancreas in response to rising blood glucose after a meal. In a person with normal insulin sensitivity, a modest rise in insulin is sufficient to keep blood glucose within a healthy range. In insulin resistance, far greater amounts of insulin are needed to achieve the same effect. This state of hyperinsulinaemia places sustained demand on the pancreas.

Several factors contribute to insulin resistance, including:

• Excess body fat, particularly visceral fat stored around the abdomen

• Physical inactivity, which reduces the muscles' capacity to take up glucose

• Chronic low-grade inflammation, associated with obesity and poor diet

• Genetic predisposition, which can increase susceptibility regardless of lifestyle

• Hormonal conditions such as polycystic ovary syndrome (PCOS) and Cushing's syndrome

• Certain medicines, including systemic corticosteroids and some atypical antipsychotics, which can impair insulin sensitivity

• Obstructive sleep apnoea, which is independently associated with impaired glucose regulation

• A history of gestational diabetes, which significantly increases the lifetime risk of developing type 2 diabetes

Insulin resistance is also closely associated with metabolic dysfunction-associated steatotic liver disease (MASLD, formerly known as non-alcoholic fatty liver disease), a condition in which excess fat accumulates in the liver and further disrupts glucose and lipid metabolism.

The progression from insulin resistance to type 2 diabetes is not inevitable. There is a recognised intermediate stage, often called prediabetes, in which blood glucose is elevated but not yet at diabetic levels. Identifying and addressing insulin resistance at this stage offers the best opportunity to prevent or delay the onset of type 2 diabetes.

How do doctors in the UK diagnose insulin resistance?

UK clinicians use HbA1c, fasting plasma glucose and occasionally an oral glucose tolerance test; an HbA1c of 48 mmol/mol or above on two occasions confirms type 2 diabetes under NICE guidance.

UK clinicians diagnose insulin resistance and its consequences primarily through blood tests that measure blood glucose and related markers, rather than by directly measuring insulin sensitivity, which is not routinely done in clinical practice. The key diagnostic tests used in NHS settings are aligned with NICE guidance and include the HbA1c (glycated haemoglobin) test, fasting plasma glucose, and occasionally an oral glucose tolerance test (OGTT).

HbA1c reflects average blood glucose over the preceding two to three months. NICE guidance uses the following thresholds:

• Below 42 mmol/mol: normal

• 42 to 47 mmol/mol: non-diabetic hyperglycaemia (prediabetes), indicating high risk

• 48 mmol/mol or above: consistent with a diagnosis of type 2 diabetes (when confirmed on a second test in the absence of symptoms)

It is important to note that HbA1c is not reliable in certain circumstances, including pregnancy, haemoglobinopathies (such as sickle cell disease or thalassaemia), conditions that alter red cell lifespan, recent significant blood loss, or recent blood transfusion. In these situations, fasting plasma glucose or an OGTT should be used instead.

Fasting plasma glucose may also be measured. A level of 6.1 to 6.9 mmol/L indicates impaired fasting glucose, and 7.0 mmol/L or above on two occasions indicates diabetes.

Random plasma glucose of 11.1 mmol/L or above, in a person with classic symptoms of diabetes (such as thirst, frequent urination and unexplained weight loss), is sufficient to confirm a diagnosis without a second test.

OGTT involves measuring blood glucose two hours after a 75 g oral glucose load. A two-hour value of 7.8 to 11.0 mmol/L indicates impaired glucose tolerance, and 11.1 mmol/L or above indicates diabetes. The OGTT is particularly used in pregnancy and in cases where other tests give borderline or unreliable results.

Doctors will also assess clinical risk factors during a consultation. The NHS Health Check programme, offered to adults aged 40 to 74 in England, includes cardiovascular and diabetes risk assessment and can identify people at elevated risk before symptoms develop.^[8] Additional investigations may include a fasting lipid profile, liver function tests (as MASLD is closely associated with insulin resistance), and blood pressure measurement.

There is no single routine blood test that directly quantifies insulin resistance in NHS practice. Surrogate markers such as fasting insulin or the HOMA-IR calculation are used in research settings but are not standard clinical tools. If you are concerned about your risk, speak to your GP, who can arrange appropriate testing.

Lifestyle changes that can improve insulin sensitivity

Reducing refined carbohydrates, increasing physical activity to at least 150 minutes of moderate-intensity exercise per week, and achieving modest weight loss are the most effective lifestyle measures for improving insulin sensitivity.

Sustained lifestyle modification is the most effective first-line intervention for improving insulin sensitivity and reducing the risk of progression to type 2 diabetes. NICE guidance recommends structured lifestyle programmes for people identified with non-diabetic hyperglycaemia, and evidence consistently shows that even modest improvements in diet and physical activity can produce meaningful reductions in blood glucose.^[1][3]

Dietary changes that support insulin sensitivity include:

• Reducing intake of refined carbohydrates and added sugars, which cause rapid rises in blood glucose

• Increasing dietary fibre through vegetables, legumes, wholegrains and fruit

• Choosing unsaturated fats over saturated fats

• Reducing overall calorie intake where weight loss is appropriate

• Limiting ultra-processed foods and alcohol

Physical activity is particularly important because skeletal muscle is the primary site of glucose uptake. Both aerobic exercise (such as brisk walking, cycling or swimming) and resistance training (such as weight-bearing exercises) improve insulin sensitivity through different but complementary mechanisms. The UK Chief Medical Officers' Physical Activity Guidelines recommend at least 150 minutes of moderate-intensity activity per week (or 75 minutes of vigorous-intensity activity), plus muscle-strengthening activities on two or more days per week. Reducing prolonged periods of sedentary time is also beneficial.

Weight loss has a dose-dependent effect on insulin sensitivity. The NHS Diabetes Prevention Programme, available in England, offers a structured behavioural intervention for people at high risk, combining dietary advice, physical activity support and psychological strategies. Referral is typically made by a GP or through the NHS Health Check.

Sleep and stress also influence insulin sensitivity. Chronic sleep deprivation and elevated cortisol from psychological stress can worsen glucose regulation. Addressing these factors, through sleep hygiene measures and stress management techniques, forms a useful adjunct to dietary and exercise changes.

Bolt Pharmacy is a GPhC-registered UK online pharmacy offering online weight-management consultations, with prescriber review and pharmacist support, which may be relevant for people exploring structured support alongside lifestyle changes. Any prescription medicine would only be considered following a clinical consultation and where judged appropriate by a prescriber.

What medicines does the NHS prescribe for insulin resistance?

Metformin is the NICE-recommended first-line medicine for type 2 diabetes; additional options include GLP-1 receptor agonists, SGLT-2 inhibitors, sulfonylureas and insulin, chosen according to individual clinical circumstances.

The NHS prescribes several medicines to manage insulin resistance and type 2 diabetes, with the choice depending on individual clinical circumstances, comorbidities and NICE recommendations. Medicines do not replace lifestyle changes but are used alongside them when blood glucose targets are not met through diet and exercise alone, or when the clinical picture warrants earlier pharmacological intervention.

Metformin remains the first-line medicine recommended by NICE for most people with type 2 diabetes. It works primarily by reducing hepatic glucose production and improving peripheral insulin sensitivity. It is generally well tolerated, has a long safety record, and is associated with a low risk of hypoglycaemia when used alone. Common side effects include gastrointestinal symptoms such as nausea and diarrhoea, which are often reduced by taking it with food or using a modified-release formulation.

Sulfonylureas (such as gliclazide) stimulate insulin secretion from the pancreas and are used when metformin alone is insufficient or not tolerated. They carry a risk of hypoglycaemia and weight gain, and NICE guidance recommends individualised assessment when considering them.

Pioglitazone is a thiazolidinedione that improves insulin sensitivity in peripheral tissues. It is an option in certain clinical situations per NICE, though it is associated with fluid retention, weight gain and an increased risk of fractures, and is not suitable for everyone.^[6]

GLP-1 receptor agonists, such as semaglutide (available as Ozempic for type 2 diabetes and Wegovy for chronic weight management, including doses up to 7.2 mg by injection) and liraglutide (Saxenda for weight management), stimulate insulin secretion in a glucose-dependent manner, reduce glucagon release and slow gastric emptying. Dulaglutide is another GLP-1 receptor agonist available in the UK for type 2 diabetes. Tirzepatide (Mounjaro) is authorised in the UK both for type 2 diabetes and for chronic weight management, and acts on both GLP-1 and GIP receptors.^[10][11] An oral formulation of semaglutide for weight management (Wegovy 25 mg tablets) has also received UK authorisation; this is a distinct product from Rybelsus, which is licensed for type 2 diabetes.^[12][7]

SGLT-2 inhibitors (such as dapagliflozin and empagliflozin) reduce blood glucose by promoting urinary glucose excretion and have demonstrated cardiovascular and renal protective benefits in clinical trials.^[17][18]

DPP-4 inhibitors (such as sitagliptin) enhance the body's own incretin response and are generally well tolerated, though less potent than GLP-1 receptor agonists.

Insulin therapy may be required when other medicines are insufficient to achieve glycaemic targets, or at diagnosis in people presenting with significant hyperglycaemia. There are several insulin types and regimens, and the choice is individualised in discussion with a diabetes team.

NICE technology appraisals guide which medicines are recommended for NHS use, and local Integrated Care Boards (ICBs) make commissioning decisions about availability within their areas. Your GP or diabetes team will advise on the most appropriate option for your individual circumstances.

Long-term health risks and how to reduce them

Cardiovascular disease, diabetic kidney disease, retinopathy and peripheral neuropathy are the main long-term risks; they can be substantially reduced by maintaining HbA1c within agreed targets, controlling blood pressure and cholesterol, and attending all recommended screening.

Unmanaged insulin resistance and type 2 diabetes significantly increase the risk of serious long-term complications affecting multiple organ systems, but many of these risks can be substantially reduced through sustained management of blood glucose, blood pressure and cholesterol. Understanding these risks helps people make informed decisions about their care.

Cardiovascular disease is the leading cause of death in people with type 2 diabetes. Insulin resistance is closely linked to dyslipidaemia (raised triglycerides and low HDL cholesterol), hypertension and endothelial dysfunction, all of which accelerate atherosclerosis. NICE recommends statin therapy for most people with type 2 diabetes to reduce cardiovascular risk, alongside blood pressure management.^[16] Statin therapy requires individualised assessment and is contraindicated in pregnancy; your GP or diabetes team will advise on what is appropriate for you.

Diabetic kidney disease (nephropathy) develops in a significant proportion of people with longstanding poorly controlled diabetes. Regular monitoring of kidney function (eGFR) and urinary albumin-to-creatinine ratio (ACR) is recommended by NICE to detect early changes. Lower blood pressure targets may apply in the presence of kidney disease.

Diabetic eye disease (retinopathy) can progress silently. It is worth noting that a period of rapid improvement in blood glucose control can transiently worsen retinopathy in some people, and those with pre-existing pre-proliferative or proliferative retinopathy should be monitored closely by an ophthalmologist during any such period.^[21] The NHS Diabetic Eye Screening Programme offers annual retinal photography to all people with diabetes.

Peripheral neuropathy and foot complications are also common, and NICE recommends annual foot checks for all people with diabetes. Any new foot ulcer, wound that is not healing, or signs of infection in the foot should be assessed promptly by a healthcare professional.

Reducing long-term risk involves:

• Maintaining HbA1c within individually agreed targets

• Controlling blood pressure (typically below 140/90 mmHg, or lower in the presence of kidney or eye disease, per NICE guidance)

• Managing cholesterol with lifestyle measures and, where indicated, statins

• Attending all recommended screening appointments

• Not smoking, and seeking support to stop if needed

If you experience symptoms such as chest pain, sudden vision changes, or signs of a serious infection affecting the feet, call 999 or go to A&E immediately. For urgent but non-emergency concerns, contact NHS 111, or speak to your GP for ongoing management queries. Suspected side effects from any medicine can be reported to the MHRA via the Yellow Card scheme at yellowcard.mhra.gov.uk.

Scientific References

1. Type 2 diabetes: prevention in people at high risk (PH38).
2. Type 2 diabetes in adults: choosing, reviewing and stopping medicines (NG28) – visual summary.
3. Type 2 diabetes in adults | Quality standards (QS209) – Preventing type 2 diabetes.
4. Diabetes | Treatment summaries – BNF.
5. Type 2 diabetes | Treatment summaries – BNF.
6. Pioglitazone | Drugs – BNF.
7. Semaglutide | Drugs – BNF.
8. NHS Health Check.
9. Diabetes – NHS.
10. Tirzepatide – NHS medicines.
11. MHRA authorises diabetes drug Mounjaro (tirzepatide) for weight management and weight loss.
12. First GLP-1 tablet for weight loss approved in the UK.
13. UK Chief Medical Officers' Physical Activity Guidelines.
14. Physical activity guidelines for adults aged 19 to 64 – NHS.
15. Diabetes in pregnancy: management from preconception to the postnatal period (NG3).
16. Cardiovascular disease: risk assessment and reduction, including lipid modification (NG238).
17. Empagliflozin for treating chronic heart failure with reduced ejection fraction (TA773).
18. Packer M et al. Cardiovascular and Renal Outcomes with Empagliflozin in Heart Failure. N Engl J Med. 2020..
19. Chronic kidney disease: assessment and management (NG203).
20. Summary report of inconsistent advice on blood pressure targets – NG17 update.
21. NG242 Diabetic retinopathy: management and monitoring – evidence review C (early worsening of retinopathy).

Frequently Asked Questions