Insulin Resistance Is Rising and We Still Don't Fully Understand Why

Insulin Resistance Is Rising and We Still Don't Fully Understand Why

In 1921, insulin was a miracle. Before its discovery, a Type 1 diabetes diagnosis was a death sentence. Children withered, starved despite eating, and died within months. Insulin changed that. It turned a fatal metabolic catastrophe into a condition people could manage for decades.

But a century later, we face a stranger problem. Not too little insulin, but too much of it doing too little. The body churns out the hormone, cells barely respond. The pancreas works harder, pumps more insulin, and eventually burns out. This is insulin resistance, and it is now the metabolic condition of our time. It is linked to obesity, fatty liver disease, heart attacks, polycystic ovary syndrome, and a dozen other disorders that quietly drain years off lives (Li et al., 2022).

The strange thing is this: we still do not fully understand why it happens. We know pieces. We know fat cells release inflammatory signals. We know genetics plays a role. We know that sitting on a couch eating processed food is probably not helping. But the mechanism, the actual molecular chain of events that makes a muscle cell stop listening to insulin, remains surprisingly murky. A 2022 review in Signal Transduction and Targeted Therapy by Mengwei Li, Xiaowei Chi, Ying Wang, and Sarra Setrerrahmane took stock of what we know and what we do not. Their conclusion is both sobering and hopeful: we have identified the players, but we are still mapping the game (Li et al., 2022).

This is what they found, and why it matters more than you think.

The Paradox at the Heart of Insulin Resistance

Insulin is a key. It unlocks cells so glucose can enter. That is the simple version. The real story is more interesting. Insulin does not just open doors. It tells cells to store fat, build protein, and stop producing glucose. It is a master regulator, a hormone that coordinates the body's energy economy across multiple tissues at once.

Insulin resistance is when that system breaks. The key still fits the lock, but the lock does not turn properly. The cell stops responding to insulin's signal. Glucose builds up in the blood. The pancreas, sensing high blood sugar, releases more insulin. The cells resist even more. It is a feedback loop that spirals toward diabetes, cardiovascular disease, and metabolic dysfunction (Li et al., 2022).

Here is the paradox: not everyone who is obese develops insulin resistance. Some people carry significant body fat and remain metabolically healthy. And some thin people develop severe insulin resistance. Something else is going on.

Li and colleagues reviewed hundreds of studies to map what that something might be. They found that insulin resistance is not one thing. It is a convergence of failures across multiple tissues, each contributing in different ways.

What Fat Cells Are Actually Doing to You

For years, we thought fat was just storage. A passive warehouse for excess calories. We now know that is wrong. Adipose tissue, the scientific name for body fat, is an active endocrine organ. It secretes hormones, inflammatory signals, and metabolites that travel through the bloodstream and influence every other tissue in the body (Li et al., 2022).

When fat cells become overloaded, they start sending distress signals. They release cytokines, small proteins that trigger inflammation. They release adipokines, hormone-like molecules that directly interfere with insulin signaling. They release free fatty acids, which accumulate in the liver and muscle and poison the insulin response from the inside.

Li and colleagues describe this process as a cascade. The adipose tissue becomes dysfunctional, not just full. It stops storing fat properly. Fat begins to spill into the bloodstream and deposit in places it does not belong: the liver, the pancreas, the muscles. This ectopic fat deposition is one of the strongest drivers of insulin resistance (Li et al., 2022).

The authors point out that not all fat is created equal. Visceral fat, the kind that wraps around your organs, is far more dangerous than subcutaneous fat, the kind under your skin. Visceral fat releases more inflammatory signals and is more prone to dysfunction. This is why waist circumference is often a better predictor of insulin resistance than body mass index.

The Liver Is Not Just a Bystander

The liver plays a central role in glucose metabolism. It stores glucose as glycogen and releases it when blood sugar drops. It also produces new glucose from scratch, a process called gluconeogenesis. Insulin normally tells the liver to stop producing glucose. In insulin resistant states, that signal fails. The liver keeps churning out glucose even when blood sugar is already high (Li et al., 2022).

This is one of the earliest signs of trouble. Fasting blood glucose rises, not because the pancreas is failing, but because the liver is ignoring insulin's command to stop.

Li and colleagues highlight a related condition: metabolic dysfunction associated fatty liver disease, or MAFLD. This is essentially fat accumulation in the liver that is not caused by alcohol. It affects roughly one in four adults worldwide. And it is tightly linked to insulin resistance. The liver becomes inflamed, scarred, and progressively less responsive to insulin. The relationship is bidirectional: insulin resistance promotes fat accumulation in the liver, and liver fat worsens insulin resistance (Li et al., 2022).

The authors note that MAFLD is now the most common chronic liver disease globally, and its rise parallels the rise in insulin resistance. They argue that the liver is not just a victim of insulin resistance but an active driver of it.

Muscle Cells Stop Listening

Skeletal muscle is the largest insulin sensitive tissue in the body. It accounts for the majority of glucose disposal after a meal. When muscle becomes insulin resistant, the body has nowhere to put the glucose. It stays in the bloodstream, driving up blood sugar and forcing the pancreas to work harder (Li et al., 2022).

Li and colleagues describe the molecular breakdown inside muscle cells. Insulin normally activates a signaling cascade that ends with glucose transporters moving to the cell surface to pull glucose inside. In insulin resistant muscle, that cascade is disrupted at multiple points. The insulin receptor itself may be downregulated. The downstream signaling proteins may be less active. The glucose transporters may fail to translocate properly.

The authors emphasize that this is not a simple on off switch. It is a gradual loss of sensitivity, influenced by lipid accumulation, inflammation, and mitochondrial dysfunction. Fat metabolites called diacylglycerols and ceramides accumulate inside muscle cells and directly interfere with insulin signaling (Li et al., 2022). This is why exercise is so effective at improving insulin sensitivity. Exercise forces muscles to burn fat, clearing out those toxic metabolites and restoring the signaling pathway.

The Inflammation Connection

One of the most consistent findings in insulin resistance research is the presence of chronic low grade inflammation. Not the kind that makes you feel sick, but a persistent smoldering immune response throughout the body. Li and colleagues found that inflammatory cytokines like tumor necrosis factor alpha and interleukin 6 are elevated in people with insulin resistance and directly impair insulin action (Li et al., 2022).

The source of this inflammation is often the adipose tissue itself. As fat cells expand, they attract immune cells called macrophages. These macrophages cluster around dying fat cells and release inflammatory signals. The inflammation spreads to the liver, muscle, and pancreas, creating a systemic environment that disrupts insulin signaling everywhere.

The authors note that this is not just correlation. Blocking inflammation in animal models improves insulin sensitivity. But clinical trials with anti inflammatory drugs in humans have been mixed. The relationship is more complex than simply inflammation equals insulin resistance. The timing, the specific cytokines involved, and the tissue context all matter.

Genetics Loads the Gun, Environment Pulls the Trigger

Not everyone is equally susceptible to insulin resistance. Li and colleagues reviewed the genetic evidence and found dozens of gene variants associated with increased risk. Some affect insulin signaling directly. Others influence fat distribution, inflammation, or mitochondrial function. But no single gene explains more than a small fraction of the risk (Li et al., 2022).

The authors describe insulin resistance as a polygenic condition, meaning many small genetic effects add up. And those genetic effects only become apparent in the right environment. A person with high genetic risk may remain perfectly healthy if they are lean, active, and eat well. The same person in a calorie dense, sedentary environment may develop severe insulin resistance.

This is why the global rise in insulin resistance is not simply a genetic epidemic. Our genes have not changed much in the last fifty years. Our environment has changed dramatically. Li and colleagues argue that the interaction between genetics and environment is where the real story lies. We need to understand not just which genes matter, but how they interact with diet, exercise, sleep, stress, and the microbiome.

What We Still Do Not Know

For all that we have learned, the authors are honest about the gaps. Here are the major open questions they identify:

• ▸Why do some obese people remain insulin sensitive while some lean people become insulin resistant? The authors suggest that fat distribution, inflammation status, and mitochondrial health may be more important than total body fat. But the exact protective factors are not fully understood (Li et al., 2022).

• ▸What is the role of the gut microbiome? Recent research suggests that gut bacteria influence insulin sensitivity through metabolites they produce. But the mechanisms are still being worked out.

• ▸Can insulin resistance be reversed once it is established? Lifestyle interventions work, but the degree of reversibility varies widely between individuals. Some people normalize their insulin sensitivity with weight loss and exercise. Others improve but never fully recover.

• ▸Why do some tissues become resistant while others remain sensitive? In many people, muscle becomes resistant before the liver, and the liver before the pancreas. The authors note that the tissue specific nature of insulin resistance is poorly understood.

• ▸What is the exact molecular trigger? We know many things contribute, but we do not know which is the first domino to fall. Is it lipid accumulation in muscle? Inflammation from adipose tissue? Mitochondrial dysfunction? The answer may be different for different people.

What This Actually Means

The 2022 review by Li and colleagues does not offer a simple solution. But it clarifies what we are dealing with. Insulin resistance is not a single disease. It is a final common pathway for multiple failures across multiple tissues. Here is what that means in practical terms:

• ▸Weight loss helps, but not all weight loss is equal. Losing visceral fat, the kind around your organs, is far more important than losing subcutaneous fat. Exercise and dietary changes that specifically target visceral fat may be more effective than simple calorie restriction.

• ▸Inflammation matters more than we thought. Reducing chronic inflammation through diet, exercise, sleep, and stress management may improve insulin sensitivity even without significant weight loss.

• ▸The liver is a critical target. Fatty liver disease is both a consequence and a driver of insulin resistance. Interventions that reduce liver fat, such as low carbohydrate diets or certain medications, may break the cycle.

• ▸Muscle is the largest glucose sink. Exercise is not optional. It directly clears the toxic lipid metabolites that interfere with insulin signaling in muscle. No pill can replicate this effect.

• ▸There is no one size fits all treatment. Because insulin resistance arises from different combinations of genetic and environmental factors in different people, effective treatment will likely require personalized approaches. What works for one person may not work for another.

• ▸We still need better tools. No medication is currently approved specifically to treat insulin resistance (Li et al., 2022). Lifestyle changes remain the most effective intervention. But the authors argue that understanding the molecular mechanisms will eventually lead to targeted therapies that address the root causes rather than just managing the downstream consequences.

The centenary of insulin discovery is a reminder of how far we have come. But it is also a reminder of how much we still do not know. We turned diabetes from a death sentence into a chronic condition. The next challenge is to understand why so many bodies are now resisting the very hormone that saved them. We have the pieces. We are still putting the puzzle together.