What is insulin resistance?

Let’s start here: What does insulin do? And what does insulin resistance mean?

Insulin sensitivity is how efficiently your cells respond to insulin, a hormone produced by the pancreas that is responsible for regulating blood sugar levels. When you’re insulin sensitive, your body efficiently uses glucose as an energy source. But when that response weakens, it leads to insulin resistance—a condition where your cells no longer respond properly, causing blood sugar and insulin levels to rise. This, in turn, increases your risk for chronic health conditions: type 2 diabetes, cardiovascular disease, or Alzheimer’s disease.

Insulin resistance is a ‘silent warning’ that’s often overlooked. 

Many live with early signs of insulin resistance without realizing the long-term impact it can have on their health. Understand the symptoms. Consistently test and track key biomarkers and take actionable steps to improve insulin sensitivity. This is taking control of your health.

Underlying Causes

Insulin resistance is a complex metabolic condition with multiple contributing factors. And to know how to reverse insulin resistance is to understand the root causes:

1. Poor Diet

A diet high in refined carbohydrates and sugars causes frequent blood sugar spikes and an increase in insulin. It’s a major driver of insulin resistance.

2. Sedentary Lifestyle

Without regular physical activity, your body’s ability to use insulin effectively is impacted–particularly by your muscles. Over time, this can lead to higher insulin levels.

3. Poor Gut Health

An imbalance in your gut microbiota can cause systemic inflammation–eventually leading to insulin resistance.

4. Excess Body Fat

Specifically, abdominal fat is associated with insulin resistance. The accumulation of adipose tissue (body fat), particularly around the abdominal organs,  leads to increased levels of fatty acids and lipid accumulation, which impacts insulin signaling and glucose uptake into the cells.

5. Chronic Inflammation

Persistent inflammation, associated with an increase in high-sensitivity C-reactive protein (hs-CRP), interferes with insulin signaling pathways in the liver, skeletal muscle, and fat tissue.

6. Genetics

Genetics can play a part. Certain gene mutations can affect your ability to regulate insulin, or metabolize glucose and lipids. This contributes to your risk for type 2 diabetes.

7. Sleep Deprivation

Sufficient, quality sleep is non-negotiable. Chronic sleep deprivation and conditions that disrupt sleep, like sleep apnea, have been closely linked to insulin resistance.

8. Stress

Both chronic and acute stress can contribute to insulin resistance. Stress activates the HPA axis and increases secretion of certain hormones that counter-regulate insulin levels.

Signs to Watch

The symptoms of insulin resistance often present in a range of subtle and seemingly common ways. But, just because it’s common, doesn’t mean it’s normal:

• Frequent headaches
• Difficulty waking up in the morning
• Increased hunger, thirst and frequent urination
• Cravings for sugar and carbohydrates
• Irritability and mood swings
• Fatigue, particularly after meals
• Nightmares
• Difficulty falling asleep
• Weight gain, particularly around the belly
• Darkened skin patches, especially around the neck and armpits 

Many of these symptoms stem from the body's inability to properly regulate glucose levels, which affects your energy levels, mood, and metabolism. If ignored, insulin resistance can progress to prediabetes and eventually type 2 diabetes.

Chronic Disease

Insulin resistance doesn’t just impact blood sugar—it plays a crucial role in your long-term health. It is linked to a range of chronic health conditions, such as:

1. Type 2 Diabetes

As insulin resistance progresses, the pancreas compensates by producing more insulin. It’s an attempt to maintain normal (and stable) blood sugar levels. Over time, the increased demand for insulin can lead to cellular dysfunction–and type 2 diabetes.

2. Cardiovascular Disease

Insulin resistance is strongly associated with high cholesterol, high blood pressure, and systemic inflammation—all of which increase your risk of heart disease and stroke.

3. Neurodegenerative Disorders

Insulin resistance also contributes to cognitive decline and may be a significant factor in developing Alzheimer’s disease. Some even refer to Alzheimer’s as "type 3 diabetes" because of its connection to impaired glucose regulation in the brain.

4. Polycystic Ovary Syndrome (PCOS)

For women, insulin resistance is a key driver of PCOS, a hormonal disorder that can cause irregular menstrual cycles, weight gain, and infertility–amongst other symptoms.

5. Metabolic Syndrome

When your body struggles to use insulin effectively, it leads to high blood sugar, increased fat storage, and chronic inflammation. Over time, this imbalance contributes to high blood pressure, abnormal cholesterol levels, and excess belly fat—hallmarks of metabolic syndrome.

6. Obesity

Excess insulin in the body promotes fat storage, particularly around the abdomen, while also making it harder for the body to burn fat for energy. Over time, this cycle contributes to weight gain and makes losing weight more difficult–further increasing your risk of metabolic disorders.

7. Metabolic-Associated Fatty Liver Disease (MAFLD)

MAFLD is a condition where excess fat builds up in the liver. When insulin isn't working properly, your body stores more fat in the liver instead of using it for energy. Over time, this can lead to liver inflammation, scarring (fibrosis), and even more severe liver diseases like cirrhosis. MAFLD is also strongly linked to obesity, type 2 diabetes, and other metabolic disorders, making insulin sensitivity crucial for liver health.

So, knowing how to control insulin levels is the key to knowing how to reduce insulin resistance–or avoid it altogether. And that means monitoring more than just the obvious biomarkers: glucose and insulin.

Biomarkers to Track

Tracking specific biomarkers can provide valuable insight into your insulin sensitivity and overall metabolic health. Your testing playbook for insulin sensitivity includes:

Metabolic

• Fasting Glucose - HbA1c complements fasting blood glucose in diagnosing diabetes. Persistently elevated glucose levels damage the cells in the pancreas that release insulin, worsening insulin resistance.

• Insulin - Elevated fasting insulin levels indicate hyperinsulinemia, a hallmark of insulin resistance. On the contrary, low insulin levels may indicate hypoglycemia.

• HbA1c - This shows your average blood glucose levels over the past 2–3 months, with a strong correlation to insulin resistance. Elevated HbA1c levels can predict diabetes complications and cardiovascular risks.

• Leptin - Produced by adipose tissue, Leptin plays a key role in energy balance, food intake, and glucose regulation. It positively impacts glucose-insulin metabolism, and acts both centrally in the hypothalamus and peripherally in the pancreas, muscles, and liver to influence insulin sensitivity.

• Adiponectin* - This enhances insulin sensitivity by activating a compound (called AMP-activated protein kinase (AMPK)) that stimulates glucose uptake and fatty acid oxidation.

Heart

• Cholesterol/HDL Ratio - An elevated cholesterol-to-HDL ratio can signal poor metabolic health and an increased risk of heart disease.

• HDL Large - Higher levels of large HDL particles are associated with better insulin sensitivity and overall metabolic health. These particles help remove excess cholesterol from the bloodstream, reducing inflammation and cardiovascular risk.

• LDL Cholesterol - Insulin resistance can impair lipid metabolism, leading to higher LDL levels and promoting plaque buildup in your arteries. LDL on its own isn’t always harmful—its impact depends on particle size and overall lipid profile.

• LDL Small - Small, dense LDL particles are strongly associated with insulin resistance and an increased risk of cardiovascular disease. These particles are more likely to penetrate artery walls and contribute to plaque formation, leading to a higher risk of atherosclerosis.

• LDL Medium - While not as harmful as small LDL, an increased number of medium LDL can still indicate worsening insulin resistance and a higher likelihood of cardiovascular disease.

• LDL Pattern - Assesses the risk of cardiovascular disease based on cholesterol health, either Pattern A or Pattern B.

• LDL Particle Number -  LDL-P measures the total number of LDL particles in the blood. Even if LDL cholesterol levels appear normal, a high LDL-P count is often linked to insulin resistance, metabolic syndrome, and an increased risk of cardiovascular disease.

• LDL Peak Size - Refers to the most common or average size of LDL particles in your blood. This is important because smaller LDL particles are more likely to contribute to plaque buildup in arteries, increasing the risk of cardiovascular disease.

• HDL Cholesterol - There are two types of cholesterol: high-density lipoprotein (HDL) and low-density lipoprotein (LDL). Think of the H as healthy, helpful, heart-supporting cholesterol that helps reduce plaque buildup.

• Lipoprotein (a) - About 50% of people who suffer heart attacks have a normal cholesterol level. Considering this, many cardiologists believe Lp(a) to be a major driver of cardiac events. Lp(a) is a genetic marker that determines risk, particularly for those with symptoms or a family history of cardiovascular disease.

• Total Cholesterol - Cholesterol is a fatty substance produced by the liver to help with thousands of bodily functions, such as building cells, promoting hormone and brain function, and synthesizing vitamin D. Too much cholesterol in the blood can damage arteries and blood vessels and elevate the risk for stroke, heart attack, and heart disease.

• ApoB - ApoB helps transport lipids throughout the bloodstream, which is vital to your cardiovascular function. This test measures the total amount of harmful cholesterol-carrying particles in your system. Along with other lipid tests, ApoB is a powerful risk marker for cardiovascular disease.

• Non-HDL Cholesterol - Captures all types of cholesterol, minus HDL cholesterol–and is particularly relevant to those who are insulin resistant. Having high non-HDL cholesterol levels is associated with insulin resistance and an increased risk of cardiovascular disease.

• hs-CRP - hs-CRP is a marker of systemic inflammation, inflammation is strongly linked to insulin resistance. Higher hs-CRP correlates to higher fasting insulin levels.

The ratio of triglycerides to HDL also helps to measure your risk for heart disease. Triglycerides are the most common type of fat in the body that stores excess energy from your diet. An accumulation of triglycerides means there is too much fat in the blood and can indicate higher risk of a cardiac event.

Lipid abnormalities are a clear sign to take action. They can contribute to blood vessel damage, inflammation, and atherosclerosis–plaque build-up in the arteries–all of which significantly increases your risk for cardiovascular disease.

Stress

• Cortisol - Consistently high levels of cortisol makes insulin resistance worse. Cortisol works against insulin by reducing the amount the body releases and making it harder for muscles to absorb sugar from the blood.

By tracking these biomarkers, you’re able to monitor for early signs of disease and take control of your health.

Ways to Improve

The good news is that insulin sensitivity is very responsive to lifestyle changes, in that you have the power to reverse insulin resistance. With your health data in your hands, implementing science-backed strategies can make a significant impact:

1. Small Movements, More Often

Even small amounts of movement throughout the day can improve glycemic control–the ability to regulate and manage blood sugar levels. Breaking up prolonged sitting with just 2–3 minutes of movement every 45 minutes has been found to reduce post-meal blood sugar spikes.

2. Increase Soluble Fiber Intake

Consuming 15–34 grams of fiber per day, particularly soluble fiber, can slow carbohydrate absorption, reduce blood sugar spikes, and lower inflammation.

Soluble fiber is the type of fiber that dissolves in water and other bodily fluids, creating a gel-like material that feeds good gut bacteria as it passes through the GI tract. It helps to reduce your body’s ability to absorb fat, lowers blood sugar and cholesterol levels, can reduce cardiovascular disease risk, aids in digestion and lowering inflammation levels. Sources include steel-cut oats, flaxseeds, beans, and vegetables.

3. Prioritize Sleep

Getting at least one extra hour of sleep per night has been linked to improved insulin sensitivity, especially in women. Poor sleep disrupts hormonal balance, leading to increased insulin resistance and higher blood sugar levels.

How to take control

When it comes to health, a one-size-fits-all is not an effective approach. Comprehensive lab testing can help you understand your individual health status and take targeted action. Function Health offers access to over 100 advanced lab tests alongside in-depth insights from top doctors to provide individuals with the data needed to monitor early indicators of insulin resistance–and thousands of diseases–in order to make informed health decisions.

By proactively testing and addressing insulin sensitivity, you have the opportunity to not only reduce your risk of chronic diseases, but also optimize your energy levels, improve metabolic health, and feel your best on the day-to-day.

If you're experiencing any symptoms of insulin resistance, no matter how common they seem, consider monitoring your biomarkers and making small, consistent lifestyle changes. Your future health starts with the actions you take today.

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