Understanding Insulin Resistance: Why Being Fit Isn’t Enough and How to Detect It Early

By Dr. Harris Masket, MD, Internal + Sports Medicine

Key Points:

• Insulin resistance occurs when your body stops responding properly to the hormone insulin, leading to elevated blood sugar levels.
• Insulin resistance is a precursor to type 2 diabetes and is linked to weight gain, dementia, stroke and heart disease.
• This condition can even impact people who are fit and eat well, highlighting the importance of regular testing and monitoring.
• Key biomarkers, such as fasting and post-meal insulin and glucose levels, can help detect insulin resistance early.
• Jyzen offers personalized protocols using biometrics, continuous glucose monitoring, and integrative therapies to combat insulin resistance.

Insulin resistance is one of the most pervasive yet misunderstood health issues today. Often referred to as a silent killer, it can quietly wreak havoc on your body for years—without you even realizing it. And here’s the kicker: just because you’re fit, eat clean, or hit the gym regularly doesn’t mean you’re in the clear. Insulin resistance can affect anyone, regardless of how healthy or active you seem on the outside. 

While it’s widely known as a precursor to type 2 diabetes, insulin resistance can lead to elevated glucose and insulin levels, triggering a cascade of health problems long before diabetes becomes a reality. 

In this article, we’ll break down what insulin resistance really is, how it impacts more than just your blood sugar, and, most importantly, how you can detect and reverse it to restore health and vitality before serious damage is done. We’ll also explore advanced tools like continuous glucose monitors (CGMs) and cutting-edge testing methods that give you a deeper understanding of this hidden threat.

What is Insulin Resistance and Why it Happens

First, what is insulin? Insulin is a hormone made inside your body and it plays a crucial role in managing our blood sugar (glucose).  It is like a key that opens the door to your cells and lets glucose in to create energy.  Under normal conditions, like after a meal, during vigorous exercise, or when your “fight or flight” mechanism is triggered, the insulin level rises to keep your blood glucose levels normal and to help you generate the energy you need. 

Insulin resistance occurs when your body becomes less responsive to insulin. But how does that happen?  

Your body is designed to prevent elevated blood glucose levels, which can be dangerous. To avoid this, it compensates by producing more insulin, pumping out higher and higher levels until glucose stabilizes. While this elevated insulin keeps glucose within a normal range, it comes at the cost of chronically high insulin levels (we’ll discuss why that's a problem later).  

If this process continues unchecked, your body will eventually reach its insulin-production limit, and when it can't produce enough, glucose levels start to rise. These elevated glucose levels are the definition of ‘prediabetes’ and if the process continues it reaches a dangerous threshold called type 2 diabetes. To make things more complicated, some of us experience a gradual decline in insulin production over time, which can further aggravate the situation.

Causes of Insulin Resistance

There is no single cause of insulin resistance; instead, it results from a combination of genetic, lifestyle, and environmental factors.  The key contributors are:

1. Physical activity: Regular movement and exercise help keep the body sensitive to insulin.  Exercise promotes glucose entry into your muscles independent of insulin, improving insulin sensitivity and lowering levels of circulating insulin (double win!) (see these two studies for more details, 1 and 2).  Even hours after you exercise, your body is still chewing up glucose in the blood as it recovers from the exertion.  Conversely, a sedentary lifestyle leads to decreased muscle mass and poor glucose utilization, both of which contribute to insulin resistance.  Choosing the right kind of exercise is important and is what I love to work on with my patients. 
2. Fat accumulation: Fat is created as the necessary and healthy storage of energy for future use, but excess fatty tissue is strongly associated with insulin resistance.  Some types of fatty tissue are particularly notorious for producing pro-inflammatory hormones and other chemical mediators that interfere with the action of insulin, and make it harder for the body to regulate glucose.  These concerning types of fat are called visceral fat and hepatic fat, the latter of which can lead to NAFLD, a very concerning inflammatory condition of the liver.
3. Highly processed foods:  Eating a lot of highly-processed foods contributes to the development of insulin resistance in a few interesting ways.  Foods that have highly processed sugars or artificial sweeteners can cause sudden spikes in our glucose levels leading to big surges of insulin.  These highly processed foods have been shown to cause us to overeat and consume more calories in less time, contributing strongly to insulin resistance.
4. Genetics: Family history has a significant role here as well. People with a family history of type 2 diabetes and insulin resistance are at a higher risk.  If you had gestational diabetes during a previous pregnancy, then you will carry an elevated risk of developing this issue later in life.
5. Age:  Because this is a process that gradually increases over time, older adults are more susceptible to insulin resistance.  There is also a gradual decline in insulin secretion as we age, which, combined with insulin resistance, can lead to type 2 diabetes even more quickly.

Why Elevated Blood Glucose is a Problem

As we discussed earlier, insulin resistance leads to higher levels of insulin being produced to keep glucose stable. However, as insulin resistance progresses and your body’s ability to manage glucose declines, blood sugar levels start to rise. While this may begin subtly, chronically elevated glucose levels become a serious problem over time.

Even moderate, persistent increases in blood glucose can quietly damage your body. Vision loss, kidney disease, nerve dysfunction, and increased risks of heart attack, stroke, and peripheral artery disease are all linked to long-term elevated glucose. Additionally, when glucose spikes sharply and then drops quickly, it can cause significant harm to blood vessels, leading to a range of complications. Chronic high glucose also weakens the immune system, impairs brain function, and slows wound healing.

Ok, glucose is a problem, but why do we care about insulin?

While elevated glucose has clear health consequences, the high levels of insulin that accompany insulin resistance (hyperinsulinemia) also have serious implications. Chronically elevated insulin levels can drive a range of dangerous conditions beyond just blood sugar control, affecting nearly every system in the body.

Here are some of the key health impacts of hyperinsulinemia:

1. Promotion of Tumors and Cancer: Hyperinsulinemia stimulates the production of Insulin-like Growth Factor 1 (IGF-1), which promotes cell proliferation and inhibits apoptosis (programmed cell death). Over time, this can accelerate the growth of tumor cells and cancers. Hyperinsulinemia is also linked to inflammation, which fosters tumor initiation and progression.

2. Atherosclerotic Cardiovascular Disease (ASCVD)

• Hyperinsulinemia contributes to the development of atherosclerosis and cardiovascular disease through several mechanisms:
• Endothelial dysfunction leading to reduced nitric oxide production, vasoconstriction, and high blood pressure.
• Dyslipidemia, which promotes plaque buildup in arteries, contributing to atherosclerosis.
• Pro-inflammatory and pro-thrombotic states, promoting thrombosis and increasing the risk of coronary artery disease and stroke.
• Smooth muscle cell proliferation, which worsens atherosclerosis by developing plaques.

3. Early-Onset Dementia and Cognitive Decline

• Hyperinsulinemia is linked to cognitive decline, early-onset dementia, and Alzheimer’s disease through:
• Impaired amyloid clearance
• Neuroinflammation
• Vascular dementia is caused by mechanisms similar to those in cardiovascular disease, compromising blood flow to the brain.
• Oxidative stress, which damages neural tissues and contributes to neurodegeneration.

4. Weight Gain and Fat Storage: Hyperinsulinemia increases fat storage, particularly inflammatory visceral fat, which worsens insulin resistance and creates a vicious cycle of weight gain and metabolic dysfunction.

Diagnosing the Problem

Many medical practices overlook the early stages of insulin resistance and elevated glucose until a patient’s blood test hits a specific threshold—often defining them as having "Borderline Diabetes" or "Prediabetes" (with a hemoglobin A1c between 5.7% and 6.4%). There are two significant issues with this approach:

Limitations of the Hemoglobin A1c Test
While the hemoglobin A1c test is useful for assessing blood glucose levels across large populations, it’s not as reliable for individuals. Variations in red blood cell counts can cause your HbA1c to be falsely low or high, making it an unreliable indicator for personal metabolic health.

If your HbA1c result is extreme (either very high or very low), you can be more confident in its accuracy. But for most people, the number hovers near the borderline, which means relying on HbA1c alone is insufficient for catching early signs of insulin resistance or hyperinsulinemia.

Missed Early Warning Signs
The complications from insulin resistance, including glucose spikes and dips, start developing well before reaching the “borderline diabetes” range. This gradual process worsens over time, causing silent damage. By the time your glucose levels are high enough to elevate HbA1c, significant harm may already be done, and reversing the problem becomes much harder.

To truly understand your metabolic health and identify any issues early, I advocate for a comprehensive set of tests:

1. Glucose Testing in Response to Carbohydrates
This can be assessed using either the Oral Glucose Tolerance Test (OGTT) or a Continuous Glucose Monitor (CGM)—or ideally, both.

• OGTT: This test measures blood glucose at fasting and then after consuming a 75-gram carbohydrate-rich drink. While your fasting level is important, your body's response to carbs is even more telling. A sharp rise in glucose levels post-carb indicates you’re well on your way to insulin resistance and possibly type 2 diabetes. This test is common in pregnancy to screen for gestational diabetes but is equally valuable outside pregnancy.
• CGM: Continuous Glucose Monitors are wearable devices that track glucose levels in real-time over 1-2 weeks. They allow us to see how your glucose responds to meals, exercise, sleep, stress, and other daily factors, giving a clear picture of how your body manages glucose in real-world conditions.

 2. Insulin Testing

It's equally important to measure insulin levels to understand your body’s insulin response. I use a combination of fasting insulin tests and post-carbohydrate insulin tests to determine how well your body is managing blood glucose.

Many people maintain normal glucose levels by producing excess insulin, but this compensation can hide insulin resistance. Testing insulin levels helps uncover where you are on the spectrum of insulin resistance and type 2 diabetes risk. In some cases, such as with certain athletes, insulin levels may be surprisingly low due to insulin insufficiency. This combination of insulin resistance and insulin insufficiency can be particularly challenging to manage, so careful testing is crucial.

3. Comprehensive Metabolic Testing
The process of converting carbohydrates into energy is complex, and it requires a broad testing approach to fully understand. In our biometrics lab, we use advanced tests such as exercise testing, lactate testing, and resting metabolic profiles. These offer a more complete understanding of how your body manages glucose and insulin, especially as you age. Whether glucose rises in a fasting state or spikes after a high-carb meal, advanced metabolic tests give us the insights needed to effectively diagnose insulin resistance.

Solving the Problem

The best place to start is asking, “what problem are we trying to solve?” If your fasting insulin levels are low, your weight is average, and you exercise 6 hours a week but still have a fasting glucose of 115 mg/dL and an HbA1c of 5.6%, you may have borderline diabetes. The person in that situation might ask, "What else can I do?" So, let’s create some general guidelines and then get more 'diagnosis-specific' at the end.

Nutrition and Insulin Resistance

Addressing nutrition is one of the first and most impactful steps in managing insulin resistance and improving your metabolic health. A diet high in refined sugars, processed foods, and unhealthy fats contributes to poor insulin sensitivity. Eating more calories than you burn leads to fat storage, which worsens insulin resistance.

• Limit highly processed foods: Try to limit the intake of manufactured and highly processed carbohydrates. These processed carbs (like fast food or snacks in plastic wrappers) are less healthy than plant-based or whole-grain carbohydrates.
• Veggies! Eating plenty of vegetables, fruit, and some grains can be hugely beneficial. Aim for at least 7 servings of vegetables daily—ideally including the full rainbow of colors to optimize phytonutrient intake.
• Focus on Whole Grains: Whole grains such as brown rice, quinoa, and oats are rich in fiber, which slows the absorption of glucose into the bloodstream. This helps prevent spikes in blood sugar and reduces the demand for insulin.
• Protein plays a role in regulating blood sugar levels by slowing the digestion of carbohydrates. Lean protein sources, such as chicken, turkey, fish, and plant-based proteins like beans and lentils, help maintain steady blood sugar levels.
• Healthy Fats are essential for satiety and can improve insulin sensitivity when consumed in moderation. Focus on fats from sources like avocados, nuts, and olive oil.

 Large portions, particularly of high-calorie foods, can contribute to excess weight and insulin resistance. Many people use time-restricted eating, which has been shown to help decrease total caloric intake and improve metabolic health.

Exercise and Insulin Resistance

While nutrition lays the foundation for improving insulin sensitivity, exercise amplifies these benefits by training the body to use glucose more efficiently. Physical activity is one of the most effective ways to boost insulin sensitivity. Exercise helps muscle cells absorb glucose, reducing the need for insulin to regulate blood sugar.

• A balance of low-intensity endurance (like “Zone 2” training), high-intensity interval training (HIIT), and weight training is ideal for building muscle and training the body to manage glucose with less insulin.
• Recovery is equally important. Overexerting yourself can elevate cortisol levels, which leads to persistently high glucose levels. For fun, try wearing a continuous glucose monitor (CGM) during your recovery sessions and observe how your blood glucose drops as you relax.

• Weight loss, even as little as 5-10% of body weight, can significantly improve insulin sensitivity and reduce the risk of progressing from borderline diabetes to type 2 diabetes.

 If your particular challenge is having lower insulin levels—leading to energy surges and dips (like the “food coma” after a big meal)—you’ll want to combine carbohydrates with protein and fat and eat smaller portions more slowly.

For some people, managing competing demands and feeling like they’re running at full speed all day long can lead to elevated cortisol levels. In this case, exercise may feel like another stressor. A holistic yet targeted approach is needed to support both physical activity and stress management.

Conclusion

In conclusion, insulin resistance is a widespread health concern that affects many without showing early symptoms. Though it can lead to type 2 diabetes, the consequences extend far beyond, contributing to high glucose and insulin levels, cardiovascular disease, cognitive decline, and increased cancer risk.

Addressing insulin resistance requires an accurate diagnosis, so thorough testing is needed.  This must be followed by a multifaceted approach that includes improving diet, increasing physical activity, and observing our body’s response with tools such as continuous glucose monitors.

Combining these lifestyle changes with personalized diagnostic testing offers a more complete understanding of your metabolic health and enables more targeted interventions. By making these changes and seeking early diagnosis, individuals can reverse the harmful effects of insulin resistance and improve long-term health.

Action items

1. Get tested. See what your insulin and glucose levels are, both fasting and after meals and exercise. 
2. Meet with a healthcare provider who is experienced with these conditions to review your labs, family history and lifestyle. 
3. See where you can decrease your intake of highly processed foods.
4. See where you can add more activity to your day.  Adding a few 45-minute walks to your week is great for stress-relief and is one of the best treatments for insulin resistance.

If you're interested in working with Dr. Harris to assess your metabolic health and gain a clear understanding of where you stand, contact Jyzen’s Patient Care Concierge: 415-729-0449 X 123 or email Concierge@jyzen.com.