Insulin Resistance Explained: Causes, Testing, and How to Reverse It

"Doctor, I've gained 8 kilograms since starting this medication. My blood work shows my sugar is creeping up. Is it the pills?" I hear some version of this question several times a month in my psychiatry clinic. The short answer: possibly. And the mechanism behind it has a name, insulin resistance.

Insulin resistance is not just an endocrinology problem. It is one of the earliest warning signals for type 2 diabetes, cardiovascular disease, and fatty liver disease ^[1][2]. It is also a silent metabolic risk that many psychiatric patients face during long-term medication use. This article will walk you through everything you need to know: what insulin resistance actually is, why it develops, how it connects to psychiatric medications, how to test for it, and most importantly, how to turn it around.

What Is Insulin Resistance?

Insulin is a hormone produced by your pancreas. Its primary job is to signal muscles, fat tissue, and the liver to absorb glucose from the bloodstream for energy or storage. Think of insulin as a key. The insulin receptors on your cells are locks. When the key fits, the door opens and glucose enters ^[1].

Insulin resistance is what happens when those locks start to rust. The key goes in, but the door barely budges. Your body responds the only way it knows how: by making more keys. The pancreas ramps up insulin production to force the doors open. For a while, blood sugar stays normal, but the workload on your pancreas keeps climbing ^[1].

This stage is called the compensatory phase. Blood glucose looks fine on paper, but insulin levels are already elevated. Most people feel perfectly normal. Standard health screenings may not even check fasting insulin. By the time the pancreas can no longer keep up and blood sugar starts rising, you have entered prediabetes or diabetes territory. That progression typically takes years, sometimes over a decade, which is exactly why this window matters so much for early intervention.

Why Does Insulin Resistance Develop? Ectopic Fat and Chronic Inflammation

Insulin resistance does not have a single cause. It results from multiple overlapping mechanisms, but current research points to two core drivers: ectopic lipid accumulation and chronic low-grade inflammation ^[1][3][5].

Table 1. Key Mechanisms Behind Insulin Resistance

In simpler terms: when you consistently consume more energy than your body can process, excess fat starts accumulating where it should not, specifically in the liver and muscles. The bioactive lipids produced by this ectopic fat jam the insulin signalling chain ^[3][4][7]. At the same time, the adipose tissue itself becomes inflamed, releasing a cascade of inflammatory mediators that further damage insulin receptors, creating a vicious cycle ^[5][6].

This is why reducing visceral fat, not simply watching the number on the scale, is the most effective strategy for reversing insulin resistance.

What Does Insulin Resistance Feel Like?

The trickiest thing about insulin resistance is that it is virtually invisible in the early stages. Most people discover it incidentally, through routine blood work or testing ordered for another concern entirely.

That said, if you look back carefully, some clues may have been there all along:

• Expanding waistline: Particularly if your waist circumference exceeds 90 cm for men or 80 cm for women. Abdominal fat has the strongest direct link to insulin resistance
• Crashing after meals: Feeling overwhelmingly sleepy after eating is more than just a "food coma." It can reflect dramatic swings in blood sugar and insulin
• Weight that refuses to budge: You are watching what you eat, but the scale will not move. Elevated insulin actively promotes fat storage and blocks fat breakdown
• Acanthosis nigricans: Darkened, velvety patches of skin on the back of the neck, armpits, or groin. This is hyperinsulinemia stimulating keratinocyte overgrowth, and it is practically insulin resistance's calling card
• Persistent fatigue and poor concentration: When cells cannot get enough glucose for fuel, energy and focus take a hit
• Frequent hunger spikes: Blood sugar rollercoasters (sharp rises followed by steep drops) trigger intense cravings at odd hours

In my clinic, some patients come in specifically because they have gained a lot of weight after starting psychiatric medication. When I dig deeper, many of these symptoms have been quietly present for months.

Psychiatric Medications and Metabolic Risk: Why Do These Drugs Cause Weight Gain?

This is the section I feel most compelled to write clearly, because it sits squarely in my domain as a psychiatrist.

A subset of psychiatric medications, second-generation (atypical) antipsychotics in particular, have been extensively documented to increase body weight, insulin resistance, and metabolic syndrome risk. This is not an isolated side effect or bad luck. It is a pharmacological reality built into how these drugs work.

These medications affect metabolism through at least three pathways:

• Appetite amplification: Blocking histamine H1 and serotonin 5-HT2C receptors increases hunger, especially cravings for carbohydrate-rich foods
• Altered lipid metabolism: Directly promoting fat storage, with a particular predilection for visceral fat
• Direct interference with insulin signalling: Some agents (notably olanzapine) have been shown to impair insulin sensitivity independently of weight gain

But not all psychiatric medications carry the same metabolic burden. Here is how the most commonly prescribed ones compare:

Table 2. Metabolic Risk Comparison of Common Psychiatric Medications

A critical reminder: seeing this table does not mean you should stop your medication on your own. Choosing a psychiatric medication always involves balancing efficacy against metabolic risk. Some high-risk drugs are irreplaceable for certain conditions (clozapine for treatment-resistant schizophrenia being the prime example). The right move is to discuss a metabolic monitoring plan with your psychiatrist, not to quietly reduce or discontinue your medication.

In my practice, patients on high metabolic-risk medications follow this monitoring protocol:

• Baseline measurements before starting: weight, waist circumference, fasting glucose, fasting insulin, lipid panel
• Weight and waist circumference checks at months 1, 2, and 3
• Fasting glucose and lipid panel every 3 to 6 months
• If weight gain exceeds 7% of baseline, seriously consider switching medications or adding metabolic protection strategies

What Diseases Are Linked to Insulin Resistance?

Insulin resistance is not a standalone diagnosis. It functions more like common soil from which many chronic diseases grow ^[8][9][10]:

• Type 2 diabetes: Insulin resistance is the core precursor. Once the pancreas burns out from years of overwork, blood sugar control collapses
• Metabolic syndrome: Large waist circumference, elevated blood pressure, high triglycerides, low HDL cholesterol, and high blood sugar. Meet three out of five criteria and you qualify. Insulin resistance is the shared driver behind all five
• Cardiovascular disease: Hyperinsulinemia promotes atherosclerosis and endothelial dysfunction, raising the risk of heart attack and stroke
• Non-alcoholic fatty liver disease (NAFLD): Insulin resistance keeps fat accumulating in the liver, potentially progressing from simple steatosis to steatohepatitis and even cirrhosis
• Polycystic ovary syndrome (PCOS): Insulin resistance drives the ovaries to overproduce androgens, leading to irregular ovulation, menstrual irregularity, acne, and excess body hair
• Hypertension: Elevated insulin promotes renal sodium retention and sympathetic nervous system activation, directly pushing blood pressure higher
• Alzheimer's disease: Emerging research shows that the brain can develop its own form of insulin resistance. Some researchers now refer to Alzheimer's as "type 3 diabetes"

The takeaway from this list is straightforward: insulin resistance is not just "a sugar problem." It is an early alarm for your entire metabolic system. The earlier you detect it, the more diseases you can prevent.

How Do You Know If You Have Insulin Resistance? HOMA-IR and Other Tests

Standard health screenings typically check fasting glucose and HbA1c (glycated haemoglobin). Both can look perfectly normal during the early compensatory stage of insulin resistance. To catch the phase where blood sugar is still fine but insulin is already running high, you need to add fasting insulin to the panel.

Table 3. Testing Methods for Insulin Resistance

HOMA-IR (Homeostatic Model Assessment of Insulin Resistance) is the most practical metric used in clinical practice ^[1][4]. The formula:

HOMA-IR = Fasting Insulin (μIU/mL) × Fasting Glucose (mmol/L) ÷ 22.5

If your glucose report uses mg/dL, divide by 18 to convert. For example: fasting insulin 15 μIU/mL, fasting glucose 100 mg/dL (= 5.56 mmol/L). HOMA-IR = 15 × 5.56 ÷ 22.5 = 3.7. That exceeds the 2.5 threshold, indicating insulin resistance.

At your next health screening, consider asking your doctor to add fasting insulin. Most facilities can run this test. It is inexpensive and provides metabolic early warning that fasting glucose alone simply cannot offer.

Can Insulin Resistance Be Reversed? Diet, Exercise, and Weight Management

The good news: before diabetes sets in, insulin resistance is reversible. And the most effective tools are not medications. They are lifestyle changes.

Dietary Strategies

The point is not simply to eat less. It is to keep blood sugar fluctuations small:

• Cut refined carbohydrates: White rice, white bread, sugary drinks, sweets. These spike blood sugar rapidly, forcing the pancreas to flood the system with insulin
• Increase dietary fibre: Vegetables, whole grains, legumes. Fibre slows glucose absorption, flattening the blood sugar curve
• Prioritise protein and healthy fats: Include adequate protein (eggs, fish, tofu) and healthy fats (olive oil, nuts, avocado) at every meal. They prolong satiety and reduce insulin spikes
• Meal sequencing: Eat vegetables and protein first, carbohydrates last. Research shows this simple reordering can reduce post-meal glucose swings by roughly 30 to 40 percent

You do not need an extreme ketogenic diet or aggressive fasting protocol. For most people, a stable, sustainable eating pattern delivers better long-term outcomes than short bursts of radical restriction.

Exercise Strategies

Exercise improves insulin sensitivity with remarkable speed. A single session of moderate-intensity aerobic exercise (a 30-minute brisk walk) enhances insulin sensitivity for the next 24 to 48 hours.

• Aerobic exercise: At least 150 minutes per week of moderate intensity (brisk walking, swimming, cycling), or 75 minutes of vigorous intensity (running, HIIT)
• Resistance training: Two to three sessions per week. Skeletal muscle is the body's largest glucose consumer. The more muscle mass you carry, the better your insulin sensitivity
• Reduce prolonged sitting: Even if you exercise regularly, sitting for more than 8 hours a day independently reduces insulin sensitivity. Stand up and move for 5 minutes every hour

Weight Management

Weight loss is the most direct route to improving insulin resistance. Research consistently shows that losing 5 to 10 percent of body weight significantly improves HOMA-IR values. For someone weighing 80 kg, that translates to just 4 to 8 kg of clinically meaningful reduction.

For psychiatric patients whose weight gain is clearly medication-related, discussing a switch with your psychiatrist (for instance, from olanzapine to aripiprazole) may be one of the most effective strategies available. However, any medication change must happen only when psychiatric symptoms are stable. You cannot sacrifice mental health stability for the sake of metabolic improvement.

Frequently Asked Questions

Q1: Can insulin resistance actually be reversed?

Yes, and the earlier you act, the better the results. Before diabetes develops, dietary changes, regular exercise, and a 5 to 10 percent weight reduction can meaningfully restore insulin sensitivity for most people. Once diabetes has set in, reversal becomes harder and may require medication support such as metformin.

Q2: At what HOMA-IR level should I be concerned?

The normal upper limit is generally 2.0 to 2.5. Values above 2.5 suggest insulin resistance, and above 3.0 the picture becomes more definitive ^[1][4]. A single number is never the whole story, though. Your doctor should evaluate HOMA-IR alongside waist circumference, lipid levels, and blood pressure for a complete picture.

Q3: Does a normal fasting blood sugar mean I am free of insulin resistance?

Not necessarily. This is one of the most common misconceptions. During the compensatory phase, the pancreas works overtime to keep blood sugar in the normal range. So fasting glucose can look perfectly fine while fasting insulin is already elevated. The only way to catch this stage is to test fasting insulin and calculate HOMA-IR.

Q4: Will taking psychiatric medication inevitably lead to metabolic syndrome?

No. Metabolic risk varies widely across medications (see the table above) and is also influenced by individual constitution, diet, and exercise habits. Many patients on high-risk medications maintain normal metabolic markers through regular monitoring, consistent physical activity, and mindful eating. The point is awareness and active management, not resignation.

Q5: I take low-dose quetiapine for sleep. Should I worry about insulin resistance?

At low doses (25 to 100 mg), the metabolic impact of quetiapine is relatively limited, but it is not zero. If you are taking it long-term, I recommend checking fasting glucose and lipids every 6 months. If you notice weight gain exceeding 5 kg, bring it up with your psychiatrist proactively.

Q6: Is there a connection between insulin resistance and PCOS?

A strong one. Roughly 50 to 70 percent of women with PCOS also have insulin resistance ^[10]. Excess insulin stimulates the ovaries to overproduce androgens, which disrupts ovulation and triggers a cascade of symptoms. Treating PCOS often centres on improving insulin resistance through exercise, dietary changes, or metformin.

Clinical Reminders from Dr. Tam

Insulin resistance is a quiet risk. It will not make you suddenly unwell, but it silently accumulates damage in your blood vessels, liver, and pancreas. By the time fasting blood sugar starts climbing, fatty liver shows up on imaging, or blood pressure creeps upward, the process has already been underway for a long time.

As a psychiatrist, there are a few things I particularly want to emphasise:

• If you are taking psychiatric medication: Ask your doctor proactively, "What is the metabolic risk of this drug? What should I be monitoring?" A good psychiatrist will integrate metabolic surveillance into your treatment plan
• Add fasting insulin to your next health screening: A modest test fee buys you years of early warning
• Waist circumference matters more than body weight: Someone with a normal BMI but a large waist carries the same metabolic risk as someone who is obese
• Do not stop your psychiatric medication because of metabolic side effects: A relapse of psychiatric symptoms carries far greater consequences than weight gain. The right approach is to discuss adjustments with your psychiatrist while keeping your mental health stable
• Exercise is the most underrated metabolic medicine: One hundred and fifty minutes of moderate-intensity exercise per week improves insulin resistance to a degree comparable to metformin

References

1. James DE, Stöckli J, Birnbaum MJ. The aetiology and molecular landscape of insulin resistance. Nat Rev Mol Cell Biol. 2021;22(11):751-771. DOI · PubMed
2. El Dib R, Gameiro OLF, Ogata MSP, et al. Zinc supplementation for the prevention of type 2 diabetes mellitus in adults with insulin resistance. Cochrane Database Syst Rev. 2015;(5):CD005525. DOI · PubMed
3. Samuel VT, Shulman GI. The pathogenesis of insulin resistance: integrating signaling pathways and substrate flux. J Clin Invest. 2016;126(1):12-22. DOI · PubMed
4. Petersen MC, Shulman GI. Mechanisms of insulin action and insulin resistance. Physiol Rev. 2018;98(4):2133-2223. DOI · PubMed
5. Saadati S, Godini R, Reddy A, Teede H, Mousa A. Metabolic crossroads in insulin resistance: exploring lipid dysregulation and inflammation. Front Immunol. 2025;16:1692742. DOI
6. Chen L, Chen R, Wang H, Liang F. Mechanisms linking inflammation to insulin resistance. Int J Endocrinol. 2015;2015:508409. DOI · PubMed
7. Calderón-DuPont D, Torre-Villalvazo I, Díaz-Villaseñor A. Is insulin resistance tissue-dependent and substrate-specific? The role of white adipose tissue and skeletal muscle. Biochimie. 2023;204:48-68. DOI · PubMed
8. Li M, Chi X, Wang Y, Setrerrahmane S, Xie W, Xu H. Trends in insulin resistance: insights into mechanisms and therapeutic strategy. Signal Transduct Target Ther. 2022;7(1):216. DOI · PubMed
9. Sperling LS, Mechanick JI, Neeland IJ, et al. The CardioMetabolic Health Alliance: working toward a new care model for the metabolic syndrome. J Am Coll Cardiol. 2015;66(9):1050-1067. DOI · PubMed
10. Mlinar B, Marc J, Janež A, Pfeifer M. Molecular mechanisms of insulin resistance and associated diseases. Clin Chim Acta. 2007;375(1-2):20-35. DOI · PubMed

Further reading:

• Weight Gain After Quitting Smoking
• How Long Should You Take Medication for Panic Disorder?
• Depression That Won't Get Better? It Might Actually Be Bipolar Disorder