Why We Get Sick

Foreword by Dr. Jason Fung

Overview

The foreword frames a critical shift in modern medicine: while infectious diseases were the primary killers a century ago, today's greatest health threats are chronic metabolic conditions like heart disease, cancer, and diabetes. Dr. Jason Fung introduces the core argument of the book—that insulin resistance and hyperinsulinemia (high insulin levels) are the central, often overlooked, root cause behind this alarming rise in chronic illness.

The New Paradigm of Disease

He illustrates this by contrasting historical and contemporary leading causes of death, underscoring that five of the top seven killers today are metabolic in nature. This sets the stage for the book's central premise: to understand why we get sick now, we must look beyond germs and focus on the hormone insulin.

Insulin Resistance: The Unifying Culprit

Dr. Fung clarifies that insulin resistance and hyperinsulinemia are two sides of the same coin—a state where the body's cells become less responsive to insulin, prompting the pancreas to produce ever-greater amounts. He draws from his clinical experience as a nephrologist, noting the devastating and widespread complications of type 2 diabetes, which is the "prototypical state" of this condition. He stresses that the medical system fails by only diagnosing diabetes when blood glucose is already high, missing the long-developing precursor of insulin resistance.

Bridging the Clinic and the Lab

The foreword highlights Dr. Benjamin Bikman’s unique qualifications, noting how his rigorous scientific research into insulin's molecular mechanisms perfectly complements Dr. Fung's own clinical observations. He praises Bikman’s rare ability to translate complex science into accessible knowledge for a general audience, ensuring the book is both authoritative and understandable.

A Hopeful, Empowering Solution

Crucially, Dr. Fung emphasizes that the book is not just a warning but a guide to empowerment. While insulin resistance is shockingly prevalent—potentially affecting up to 85% of American adults—it is reversible. The solution is not more medication or surgery, but purposeful diet and lifestyle changes. He notes that Bikman moves beyond the simplistic "eat less, move more" model to a more effective physiological approach focused on managing insulin.

Key Takeaways

• The primary cause of sickness and death has shifted from infectious diseases to chronic metabolic disorders.
• Insulin resistance and the resulting hyperinsulinemia are the fundamental, unifying root causes of most modern chronic diseases.
• This condition develops long before a formal diagnosis of type 2 diabetes and is implicated in a vast array of health issues.
• Despite its prevalence and severity, insulin resistance can be reversed through targeted diet and lifestyle interventions, not merely managed with medication.

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Chapter 1: What Is Insulin Resistance?

Overview

Here’s a pervasive and often invisible condition affecting a staggering number of people worldwide, with estimates suggesting nearly 90% of adults in some populations could be impacted. It’s emerging in younger ages than ever before, and most who have it don’t even know. This condition is insulin resistance. To understand it, you first need to meet insulin itself—a master hormone that does far more than manage blood sugar. It acts as a cellular key, directing energy storage, growth, and function in nearly every tissue, from your liver and muscles to your fat and brain.

Yet, for over a century, medicine has been looking in the wrong place. Our diagnostic focus has been locked on blood glucose, a legacy of how diabetes was first identified. This created a critical blind spot because insulin resistance can simmer for decades, with rising insulin levels trying to compensate, long before blood glucose finally spikes and leads to a diagnosis of type 2 diabetes. In reality, type 2 diabetes is just the late, hyperglycemic stage of this deeper, more widespread problem.

Leaving insulin resistance unchecked is where the true danger lies. While not directly fatal, it acts as a powerful and reliable vehicle for a host of life-threatening diseases. It is a common root cause for disorders of the brain, like Alzheimer’s disease, the heart and blood vessels—the leading cause of death for those with the condition—and even cancers of reproductive organs. This makes tackling it one of the most important steps you can take for long-term health. The journey ahead explores exactly how this single hormonal dysfunction wreaks such havoc throughout the body. Buckle up—it’s a bumpy ride.

The Alarming Scale of a Hidden Epidemic

Insulin resistance is presented not as a rare condition, but as a pervasive and often silent global epidemic. The statistics are staggering: while official estimates suggest half of all US adults have it, the true prevalence may be as high as 88%. This is not a Western problem alone; 80% of affected individuals live in developing countries, with half the adult populations in China and India being insulin resistant. The trend is accelerating, with global cases having doubled in the past thirty years and projected to double again. Most alarmingly, the condition is appearing in younger populations, including four-year-olds, and the overwhelming majority of those who have it are completely unaware.

Understanding the Hormone at the Center of It All

To grasp insulin resistance, one must first understand insulin. It is a hormone, produced by the pancreas, with a famously known role in regulating blood glucose. After a meal, insulin acts like a key, unlocking cells to allow glucose to move from the bloodstream into tissues like the brain, heart, muscle, and fat for use or storage.

However, its influence is far more extensive. Insulin is a master anabolic hormone, affecting every cell in the body. Its specific action depends on the cell type: in the liver, it promotes fat production; in muscle, it stimulates protein synthesis; in fat tissue, it encourages fat storage. It influences energy use, cell growth, hormone production, and even cell survival from head to toe.

The Flawed Historical Focus on Glucose

The modern medical system’s focus on blood glucose as the primary marker for metabolic disease is a historical artifact with significant consequences. For millennia, diabetes was identified by its obvious symptom: sweet, glucose-laden urine. This observation linked the disease inextricably to glucose. While types 1 and 2 diabetes share this symptom, their root causes are opposites: type 1 is a lack of insulin, while type 2 is driven by too much insulin due to insulin resistance.

This critical distinction was obscured. Scientifically, glucose was far easier and cheaper to measure than insulin for most of medical history. As a result, clinical diagnostic standards were built entirely around glucose levels. This creates a major blind spot: a person can be insulin resistant for years or even decades, with elevated insulin levels, while their pancreas works overtime to keep blood glucose within the normal range. The problem only becomes officially recognized as "type 2 diabetes" when insulin resistance progresses to the point where the pancreas can no longer compensate, and blood glucose finally rises.

Thus, insulin resistance is the true underlying disease, and type 2 diabetes is its advanced, hyperglycemic stage. The book argues that by focusing on glucose, we are diagnosing the problem far too late, often missing a critical window for intervention. Insulin levels themselves are a much earlier and more predictive marker of metabolic dysfunction.

The Dire Consequences of Untreated Insulin Resistance

While insulin resistance itself is not the direct cause of death, the text powerfully frames it as a "reliable vehicle" that accelerates the development of life-threatening conditions. This is the central danger: it acts as a common, often hidden, root cause for a diverse array of serious health problems. The passage stresses that this is far from a minor metabolic hiccup—it is a serious pathological state with grave implications for long-term health and mortality.

The chapter outlines a sobering list of organs and systems harmed by this condition. Insulin resistance is implicated in disorders of:

• The Head: Notably, Alzheimer's disease is highlighted as a potential consequence.
• The Heart and Blood Vessels: Cardiovascular complications are identified as the leading cause of death for most people with insulin resistance.
• Reproductive Organs: The text links it to cancers such as breast and prostate cancer.

By connecting one underlying mechanism to so many different diseases, the author underscores a critical point for the reader: many seemingly separate health issues may share a single, addressable origin. This sets the stage for the entire premise of the book—that managing insulin resistance could have wide-ranging, protective benefits.

The final sentences serve as a direct bridge to the rest of the book. They state that understanding how insulin resistance causes these disorders is essential to appreciating insulin's vital role in health. This declarative purpose—to explore the mechanics of insulin throughout the body and its dysfunctional state—prepares the reader for the detailed science to come, ending with a note of warning and anticipation: "Buckle up—it's a bumpy ride."

Key Takeaways

• Insulin resistance is not directly fatal but is a primary driver of numerous lethal chronic diseases.
• It functions as a common root cause for diverse health problems affecting the brain, heart, blood vessels, and reproductive systems.
• The most likely outcomes of untreated insulin resistance are death from heart disease or the development of conditions like Alzheimer's and specific cancers.
• Understanding the mechanistic link between insulin resistance and these diseases is crucial, which is the focus of the upcoming chapters.

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Why We Get Sick

Chapter 2: Heart Health

Overview

At the heart of many cardiovascular issues lies insulin resistance, a condition that orchestrates a cascade of effects threatening heart health. It starts by ramping up blood pressure through several interconnected pathways. Chronically high insulin levels stimulate the release of aldosterone, prompting the kidneys to retain sodium and water, which increases blood volume. Simultaneously, excess insulin acts as a growth signal, thickening the walls of blood vessels and narrowing their passage. This structural change is compounded by a breakdown in function: insulin resistance blunts the production of nitric oxide, a compound that normally helps vessels relax and widen. To top it off, persistent hyperinsulinemia keeps the sympathetic nervous system subtly activated, constricting vessels and elevating heart rate. Together, these forces sustain hypertension.

Beyond blood pressure, insulin resistance profoundly disrupts blood lipids, leading to dyslipidemia. It shifts the body toward producing smaller, denser LDL particles (Pattern B), which are more likely to contribute to plaque formation than larger, buoyant ones. A key indicator of this risky shift is the Triglyceride-to-HDL ratio; when it climbs above 2.0, it signals a move toward more dangerous particles. While medications like statins are commonly used, they may inadvertently worsen this LDL pattern and increase the risk of type 2 diabetes, highlighting the complexity of cholesterol management.

The real danger isn't cholesterol itself but what happens to it. Cholesterol and fats become harmful only when oxidized, a process fueled by oxidative stress. Highly oxidizable polyunsaturated fats like linoleic acid from seed oils are often the primary culprits, hitching rides on cholesterol molecules. Insulin resistance exacerbates this by increasing those small, dense LDL carriers and raising oxidative stress. This oxidation triggers inflammation, a critical player in heart disease. Ironically, while insulin typically has anti-inflammatory effects, in an insulin-resistant state, it flips to promote inflammation, creating a perfect storm for atherosclerosis. Inflammation damages vessel walls, accelerates plaque formation, and is a better predictor of heart disease than cholesterol alone.

The impact even reaches the heart muscle itself. Insulin resistance is linked to cardiomyopathy, where the heart becomes weak or overly thickened. Heart muscle cells rely on glucose for energy, and insulin resistance impairs their ability to use it, leading to an energy deficit that compromises pumping efficiency. Ultimately, addressing heart disease requires confronting insulin resistance directly, as it sits at the center of blood pressure problems, lipid disorders, oxidative damage, inflammation, and heart muscle dysfunction.

Salt and Water Retention

One of the primary ways insulin resistance drives high blood pressure is through the hormone aldosterone. Insulin stimulates the adrenal glands to release aldosterone, which signals the kidneys to retain sodium. Where sodium goes, water follows. This increases overall blood volume, which in turn raises blood pressure. In an insulin-resistant state, chronically high insulin levels mean this sodium-retaining signal is constantly active, contributing to sustained hypertension. This mechanism also explains why some individuals are "salt-sensitive"—their insulin-resistant physiology prevents the proper excretion of salt, leading to fluid accumulation.

Thicker, Narrower Blood Vessels

Excess insulin acts as a potent growth signal for the cells lining blood vessels, known as endothelial cells. This is a normal anabolic function, but hyperinsulinemia causes an exaggerated response, leading to a thickening of the vessel walls. As these walls encroach inward, the passage for blood narrows. Think of a garden hose whose walls are getting thicker from the inside; the pressure inside the hose inevitably rises. This structural remodeling is a direct contributor to increased blood pressure.

Impaired Blood Vessel Dilation

Normally, insulin helps lower blood pressure by signaling endothelial cells to produce nitric oxide (NO), a powerful compound that relaxes and widens blood vessels. However, in insulin resistance, the endothelial cells become less responsive to this signal. The body's ability to produce NO in response to insulin is blunted. Consequently, blood vessels lose their capacity to dilate properly, causing blood pressure to remain elevated. This loss of vasodilation is a critical breakdown in cardiovascular regulation.

Sympathetic Nervous System Activation

Insulin also subtly activates the sympathetic nervous system—our "fight or flight" response. One effect of this activation is the constriction of blood vessels and an increase in heart rate, both of which raise blood pressure. While this is a mild, temporary effect under normal conditions, the persistent hyperinsulinemia of insulin resistance means this pressure-raising system is chronically and inappropriately "on," adding another steady push toward hypertension.

Dyslipidemia and Altered Cholesterol Profiles

Insulin resistance profoundly disrupts blood lipids, a condition known as dyslipidemia. It's not just about high "bad" cholesterol (LDL). A key insight is that the type of LDL particle matters greatly. Insulin drives the liver to produce smaller, denser LDL particles (known as Pattern B). These particles are more likely to penetrate blood vessel walls and contribute to plaque formation than the larger, buoyant LDL particles (Pattern A).

A practical way to gauge this risk is through the Triglyceride-to-HDL ratio (TG/HDL). A ratio below 2.0 suggests a healthier Pattern A profile, while a ratio above 2.0 indicates a dangerous shift toward the atherogenic Pattern B. Since insulin resistance typically elevates triglycerides and lowers HDL, it directly worsens this ratio, creating a lipid environment that aggressively promotes heart disease.

A Note on Statins

The chapter briefly addresses statins, common cholesterol-lowering drugs. It notes that while they may benefit those with specific genetic disorders, their benefit for others at risk based on conventional markers is surprisingly small. Importantly, statins may worsen the LDL pattern by increasing the proportion of small, dense Pattern B particles and have been linked to a significantly increased risk of developing type 2 diabetes, particularly in postmenopausal women.

The True Culprit: Oxidized Fats and Cholesterol

The chapter clarifies that cholesterol deposited in the blood vessel wall isn't inherently harmful; it only becomes problematic when oxidized. This oxidation occurs under conditions of high oxidative stress. Once oxidized, these lipids are engulfed by macrophages—white blood cells that digest debris. These lipid-filled macrophages become "foam cells," which recruit more immune cells, triggering an inflammatory response that forms the core of an atherosclerotic plaque.

Critically, the text shifts blame from cholesterol alone to include polyunsaturated fats, particularly linoleic acid from seed oils (like soybean oil). Linoleic acid oxidizes far more readily than cholesterol and is likely a primary culprit, often hitching a ride on cholesterol molecules. Insulin resistance fuels this process by increasing the small, dense LDL particles (Pattern B) that carry these oxidizable fats and by raising oxidative stress itself.

Inflammation: The Connecting Thread

The narrative establishes that markers of inflammation are better predictors of heart disease than cholesterol. Here, insulin resistance plays a paradoxical and damaging role. While insulin normally has anti-inflammatory effects, in insulin-resistant individuals with chronically high insulin levels, it instead activates inflammatory pathways. This places insulin resistance at the center of a perfect storm for atherosclerosis: it increases blood pressure (damaging vessel walls), promotes lipid deposition, and directly drives the inflammation that accelerates plaque formation.

Cardiomyopathy: A Failure of Fuel

The discussion extends to disorders of the heart muscle itself, known as cardiomyopathy. Insulin resistance is strongly linked to dilated cardiomyopathy (DCM), where the heart muscle becomes stretched and weak. Heart muscle cells primarily use glucose for fuel, and insulin resistance impairs their ability to take in glucose, leading to an energy deficit that compromises pumping ability. Evidence also suggests that chronically high insulin may contribute to hypertrophic cardiomyopathy by promoting excessive growth of the heart muscle.

Key Takeaways

• Atherosclerosis is driven by oxidation: Cholesterol and fats become harmful only when oxidized, a process heavily influenced by the highly oxidizable linoleic acid found in common seed oils.
• Insulin resistance is a master regulator: It promotes atherosclerosis by increasing problematic LDL particles, raising oxidative stress, and—critically—switching insulin's role from anti-inflammatory to pro-inflammatory.
• Heart disease is multifaceted: Insulin resistance contributes not only to blocked arteries but also to direct weakening of the heart muscle (cardiomyopathy) by disrupting the heart's primary energy source.
• The central cause must be addressed: The chapter concludes that successfully reducing heart disease risk requires confronting insulin resistance directly, moving beyond simply treating its symptoms.

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Chapter 3: The Brain and Neurological Disorders

Overview

This chapter explores the profound connection between insulin and brain health, dismantling the old belief that the brain was immune to insulin's effects. It details how insulin is crucial for normal cognitive functions like learning, memory, and appetite regulation, and then investigates the damaging consequences when the brain becomes insulin resistant. The narrative establishes insulin resistance as a central, contributing factor in a spectrum of neurological disorders, from Alzheimer's disease and other dementias to Parkinson's disease, migraines, and neuropathy.

Insulin’s Crucial Role in the Brain

We now understand that brain cells are studded with insulin receptors. Insulin helps these cells take in glucose for fuel, supports their growth and survival, regulates appetite, and is vital for learning and memory formation. Studies, such as one involving diabetic rats struggling to learn a maze, underscore that normal brain function is dependent on proper insulin signaling. The central problem begins when the brain becomes resistant to insulin, a state that often develops concurrently with resistance in other tissues like muscle and liver.

The Consequences of Brain Insulin Resistance

When the brain stops responding properly to insulin, its structure and function are compromised. Research indicates that prolonged insulin resistance can age the brain prematurely, with every decade of resistance making the brain appear two years older. Functionally, this leads to impaired short-term learning, potential long-term memory damage, and disrupted appetite regulation that can contribute to overeating. This state of impaired fuel access sets the stage for serious neurological diseases.

Alzheimer’s Disease as "Type 3 Diabetes"

Alzheimer's disease, the most common form of dementia, is now strongly linked to insulin resistance in the brain—a connection so significant it has earned the moniker "type 3 diabetes." While older theories focused on the accumulation of amyloid-beta plaques and tau protein tangles, insulin resistance appears to play a key role in both processes. It can increase plaque formation and promote the hyperactive tau that creates tangles. Perhaps more fundamentally, brain insulin resistance leads to "glucose hypometabolism," where the brain’s high-energy engine is starved of its primary fuel (glucose), directly impairing function. Notably, in population studies, markers of insulin resistance (like fasting insulin levels) show a stronger statistical association with Alzheimer's risk than many traditional factors like hypertension.

Other Forms of Dementia and Parkinson’s Disease

The impact of insulin resistance extends to other brain disorders. Vascular dementia, often related to impaired blood flow in the brain, is twice as likely in individuals with insulin resistance, linking back to the cardiovascular damage caused by metabolic dysfunction. Parkinson’s disease, characterized by the loss of dopamine-producing neurons, is also closely associated with insulin resistance. The relationship appears bidirectional: insulin affects dopamine signaling in the brain, and altering dopamine (e.g., via certain medications) can induce insulin resistance. A high percentage of Parkinson’s patients also have insulin resistance or type 2 diabetes.

Migraines, Neuropathy, and Other Conditions

The chapter notes associations between insulin resistance and other common neurological issues. For instance, individuals with insulin resistance are more likely to suffer from migraine headaches, possibly due to the same brain energy deficit seen in Alzheimer’s. Furthermore, neuropathy—the nerve damage often felt as tingling or burning in the extremities—can begin before the high blood sugar of full-blown diabetes appears, suggesting that insulin resistance itself is an early culprit in damaging nerve function throughout the body.

Key Takeaways

• The brain is highly responsive to insulin, which is essential for cognitive function, memory, and metabolism.
• Insulin resistance in the brain disrupts its energy supply and contributes to structural aging and functional decline.
• Alzheimer’s disease has such a strong metabolic component that it is often called "type 3 diabetes," with brain insulin resistance being a key driver of its pathology.
• The detrimental effects of insulin resistance are not limited to Alzheimer’s but are also significant risk factors for vascular dementia, Parkinson’s disease, migraines, and peripheral neuropathy.
• This new understanding reframes many neurological disorders through a metabolic lens, opening potential avenues for prevention and intervention focused on improving insulin sensitivity.

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