Insulin and insulin resistance: mechanisms, signs, and metabolic

Insulin and insulin resistance: what is really happening in the body

Insulin has become more of a cultural symbol than a hormone. On the one hand, it is demonized as the “hormone that makes you gain weight”; on the other, it is reduced to a simple regulator of blood glucose. Both readings are impoverished, because they take a coordination signal—refined, situational, deeply integrated with the liver, muscle, adipose tissue, and brain—and turn it into a moral switch: good/bad, on/off, controllable/uncontrollable.

Insulin resistance, in this context, is often described as “high sugar.” But physiologically, another formulation is more accurate: it is a change in how certain tissues interpret and translate the insulin signal. It can begin with perfectly normal blood glucose levels, sustained by pancreatic compensation. And it can evolve in different ways depending on where the main problem lies (liver, muscle, fat), the distribution of adipose tissue, sleep, circadian rhythms, stress, and chronic energy load.

This article is not meant to “optimize insulin.” It is meant to understand why the signal loses clarity, which biological trade-offs make that plausible (at first) and costly (over time), and how to read markers and symptoms without turning them into self-diagnosis or an ideological war against a macronutrient.

When insulin stops being “the key”: a signal that loses clarity

The “key-lock” metaphor became popular because it is intuitive: insulin would be the key that opens cells to glucose. But real physiology is not a single door with a faulty lock. It is a network of tissues with different priorities, partially independent signaling pathways, and different timing. That is why insulin resistance is often selective: some functions of insulin are blunted, others remain active, and still others become paradoxically overactive.

Under normal conditions, insulin is a hormone of postprandial energy coordination. After a meal, it helps to: - reduce hepatic glucose production (by suppressing gluconeogenesis and glycogenolysis); - facilitate glucose uptake in muscle and adipose tissue (mainly through GLUT4 translocation); - restrain lipolysis in adipose tissue (reducing the release of free fatty acids); - signal a state of “energy abundance,” also influencing circuits involved in appetite and behavior.

So when talking about insulin resistance, the useful question is not “is insulin there or not?”, but rather: how coherent is the signal with respect to the context, and how much response does it produce in different tissues? This is where a distinction that is often lost becomes important: - compensatory hyperinsulinemia: the pancreas increases secretion to keep blood glucose in range; - hyperglycemia: regulation can no longer keep up (because resistance increases, because beta-cell capacity declines, or both).

This difference explains why many people “look fine” on standard lab tests for years: glucose can remain normal while insulin is working harder. And this is where insulin resistance should be seen as a continuum, not a binary label: it is not a switch that flips one day, but a trajectory.

Another more mature framework is to consider it an adaptation that becomes costly. In a body exposed to chronic energy load, sedentary behavior, disrupted rhythms, and the accumulation of ectopic fat, reducing sensitivity in some tissues may be—initially—a form of protection against overload. But that trade-off reduces metabolic flexibility: the body becomes less able to nimbly manage the alternation between storing and using energy. And when flexibility declines, the “costs of regulation” increase: more insulin to achieve the same effect, more subjective fluctuations, more pressure on the liver and, over time, on the pancreas.

The architecture of insulin resistance: liver, muscle, and adipose tissue do not fail in the same way

Talking about insulin resistance “in general” is convenient, but often imprecise. The phenomenon takes different forms in three key organs: liver, muscle, adipose tissue. And the main site changes what we observe in markers and what we “feel” in daily life.

In the liver, insulin should reduce endogenous glucose production. When hepatic insulin resistance is present, the liver continues producing glucose even when it would not be necessary. The typical result is an increase in fasting blood glucose or a tendency for it to rise. But above all, the liver is also a central hub for lipids: when some pathways remain sensitive to insulin (for example lipogenic ones) while others do not (suppression of gluconeogenesis), a favorable setting is created for elevated triglycerides and hepatic steatosis.

In muscle, the issue is different: it is the largest “reservoir” for disposing of postprandial glucose. Muscle uptake depends heavily on GLUT4 translocation and on the muscle’s ability to use or store energy (glycogen). If the muscle is underused (sedentary lifestyle, low mass, or low contractile activity), it can become less responsive. Here the typical consequence is poorer blood glucose handling after meals rather than in the fasting state. This is not a minor detail: many people have acceptable fasting values but high peaks and slow declines after meals.

In adipose tissue, insulin acts as a brake on lipolysis. If that brake weakens, free fatty acids (NEFA) increase in circulation. These NEFAs fuel resistance in other organs and promote ectopic deposition: liver and muscle become “filled” with lipids and intermediates that disrupt insulin signaling. It is a systemic dynamic: fat is not just “weight,” it is an endocrine and immunological organ.

Finally, distribution matters more than the number on the scale. Visceral fat and ectopic fat (in the liver, in muscle) are more closely linked to dysmetabolism than subcutaneous fat. That is why two people with the same BMI can have different metabolic profiles: one with visceral accumulation may show higher triglycerides, lower HDL, fatty liver, and earlier signs of resistance.

This architecture also helps avoid a common mistake: looking for “the single cause.” Often, it is a convergence of sites and signals that, taken together, makes the system less responsive.

What happens at the cellular level: insulin signaling, intracellular lipids, and low-grade inflammation

At the cellular level, insulin resistance does not mean that insulin “doesn’t get in.” It means that the signal is translated less effectively into specific actions. The classic pathway, simplified but faithful, is:

insulin receptor → IRS (insulin receptor substrate) → PI3K/AKT → metabolic effects, including: - translocation of GLUT4 to the membrane (muscle and adipose tissue); - increased glycogen synthesis; - modulation of lipolytic and lipogenic processes.

In many contexts, the problem is not glucose itself but the intracellular lipid load. When the energy available (especially in the form of lipids) exceeds the tissue’s capacity to oxidize it or store it in a “safe” way, intermediates such as diacylglycerols (DAG) and ceramides increase. These molecules can interfere with signaling nodes (for example by promoting the “wrong” phosphorylation of IRS or altering AKT), reducing the effectiveness of the insulin signal. This is one reason why resistance can be observed even without “high sugars” in the early phases: the cell is under energy and lipid load.

Then there is the issue of mitochondrial oxidative capacity. Mitochondria are not a talisman, but they represent the ability to use energy substrates efficiently. If the chronic arrival of energy exceeds demand (little muscle contraction, many dense meals, irregular rhythms), stress signals accumulate: reactive species, redox alterations, metabolic congestion. Again, this is not the “fault” of a single choice, but of repeated systemic pressure.

Inflammation often enters the picture as low-grade metabolic inflammation: not the acute picture that can be “felt,” but a chronic activation of immune signals and cellular stress (endoplasmic reticulum stress, cytokines such as TNF-α and IL-6 in specific contexts, macrophage infiltration in adipose tissue). Visceral adipose tissue in particular tends to be more pro-inflammatory. This environment further alters insulin signaling and facilitates a vicious cycle: more load → more stress → less sensitivity → more insulin required → more pressure on the system.

One often-overlooked point is selective resistance. In the liver, for example, some pathways leading to lipogenesis may remain relatively sensitive to insulin while suppression of glucose production is blunted. The result is a paradox: simultaneously more glucose produced and more lipids synthesized/accumulated. Clinically, this is reflected in elevated triglycerides, steatosis, and worsening of the cardiometabolic profile.

If you want a psychologically mature framework: insulin resistance is not weakness, nor a “lack of discipline.” It is physiology under load, with trade-offs that make sense in the short term and carry costs in the long term.

Hyperinsulinemia: useful compensation or an independent problem?

For years, the story can be this: sensitivity declines, the pancreas responds by increasing insulin, and blood glucose remains apparently “fine.” This is the phase that makes insulin resistance difficult to recognize and, above all, easy to trivialize. Beta-cell compensation is a remarkable capacity: it prevents hyperglycemia as long as it holds.

But compensation is not neutral. Chronically higher insulin, especially in an environment of energy abundance and disordered rhythms, can have perceived and biological costs. Subjectively, some people report: - greater hunger or difficulty feeling stably full; - fluctuations in energy and concentration after rich or irregular meals; - postprandial sleepiness, cravings, a need to “pick themselves back up” with coffee or sugar.

These signals, however, are non-specific. They can depend on poor sleep, stress, meal composition, timing, alcohol, sedentary behavior, and also expectations. The modern risk is overinterpretation: attributing every dip in energy to insulin, creating metabolic anxiety and obsessive control.

Biologically, compensation also means more work for the beta cells. In some people, because of genetics, age, body composition, or ectopic accumulation, this compensation lasts less long. When beta-cell capacity is no longer adequate for the degree of resistance, blood glucose rises: first postprandially (prediabetes), then also in the fasting state, up to criteria for type 2 diabetes. It is not an inevitable path, but it is a possible trajectory.

This structure is useful because it avoids two opposite errors: believing that “as long as glucose is normal, there is nothing there,” and believing that “if insulin is high, it is already diabetes.” In reality, the clinically sensible question is: how sustainable is compensation over time, and which system-level levers can reduce the load?

How to read markers without reductionism: glucose, insulin, HbA1c, and lipid clues

Markers are partial maps. Used well, they help orient us. Used badly, they become a tribunal. And insulin resistance is a typical case in which simplification produces confusion.

Fasting glucose: mainly reflects the balance between hepatic glucose production and basal use. It is useful, but it can remain normal even when the pancreas is compensating with more insulin. It is also sensitive to acute stress, infections, poor sleep, and the timing of the last meal.

Fasting insulin: it can provide a clue about compensation, but it is more variable: differences between laboratories, pulsatile secretion, influence of stress and sleep restriction. A single number, without context, says little.

HOMA-IR: this is an index derived from fasting glucose and insulin. It may suggest a trend, especially at the population level, but it is not an individual “verdict”: cutoffs differ across groups, sensitivity is limited in some conditions, and it does not clearly distinguish hepatic from peripheral involvement.

HbA1c: describes an average glycemic exposure over about 2–3 months. It is valuable for assessing trajectories, but it can mislead if red blood cell turnover is altered (anemias, hemoglobinopathies, some kidney conditions) or if blood glucose is highly variable: an “average” can hide spikes.

OGTT (oral glucose tolerance test) and, in some cases, insulin measurements during the test, can clarify the postprandial response. This is not a test to do out of curiosity: it makes sense if there is a clinical question (risk factors, borderline markers, family history, steatosis, etc.) and if interpreted with a physician.

On the lipid side, elevated triglycerides, low HDL, and an unfavorable TG/HDL ratio are frequent clues to dysmetabolism and associated insulin resistance, often in the presence of visceral fat or fatty liver. They are not diagnoses, but context. Transaminases (ALT/AST) and imaging findings compatible with steatosis can also be pieces of the puzzle.

The aim here is literacy, not self-diagnosis. If markers become a control project, the most important question is often lost: what in the life-body system is making such a “high” or frequent insulin signal necessary?

Why it arises and persists: energy balance, sleep, circadian rhythms, and stress as everyday biology

In most cases, insulin resistance does not arise from a single culprit. It arises from a convergence: high available energy, low demand, misaligned rhythms, chronic stress, with individual variability.

Chronic energy overload is not just “eating too much.” It is also eating in a way that brings energy in when demand is low, and repeating this pattern for years. If actual oxidation (what the body uses) remains lower than intake, some of that energy has to go somewhere: adipose storage, but also ectopic deposition. And ectopic deposition is what most often disrupts signals.

Here muscle is crucial, not as a “calorie burner,” but as an organ that, through contraction, increases glucose uptake even independently of insulin. It is a biological signal: the body interprets contraction as energy demand, and this changes substrate handling. When muscle is not called upon to work, the whole system loses a fundamental postprandial disposal pathway.

Sleep is a powerful modulator. Sleep restriction and irregularity worsen insulin sensitivity and increase the likelihood of denser food choices. Circadian misalignment (shift work, nighttime light exposure, late meals) also shifts physiology toward less efficient glucose handling. It is not a matter of “discipline”: the body is simply better prepared to handle energy in certain time windows.

Stress too has two faces. Acute stress can be adaptive: it mobilizes energy. Chronic stress, with the HPA axis constantly activated, tends to keep glucose availability higher (gluconeogenesis), influence appetite and behavior, and worsen sleep and recovery. Here it is useful to remember that exercise and stress are not simple opposites: training can reduce anxiety and improve regulation, but in some conditions it can also disturb sleep if poorly timed or excessive—a topic explored in more depth here: Why training “calms you down” but can also keep you awake: the biological ambivalence of exercise on anxiety and sleep.

Food quality matters as context: energy density, fiber, food matrix, protein share, level of ultra-processing. “Carbohydrates = bad” is a cultural shortcut. High-fiber carbohydrates within an intact food matrix behave differently from liquid sugars and ultra-processed products. And above all: the same meal, in a body that sleeps well and moves, produces a different profile than in a body marked by sedentary behavior and disrupted rhythms.

Finally, alcohol and the liver: even with a “clean” diet, alcohol can worsen triglycerides and steatosis by interfering with hepatic lipid handling. It is an example of how the problem is systemic: it is not enough to be virtuous on one axis while neglecting the others.

What tends to improve insulin sensitivity (and what promises too much)

If insulin resistance is an adaptation to load, improving sensitivity means reducing that load and increasing signals of use. The most robust physiological priorities, in the literature and in clinical practice, are less glamorous but more solid: - reducing visceral and ectopic fat (liver, muscle); - increasing or maintaining muscle mass and function; - improving sleep and rhythm regularity; - reducing how often the body has to “manage too much” (in terms of energy, timing, and stress).

Nutritionally, the adult path is structure, not ideology. When weight loss is needed, a sustainable energy deficit is often the most effective lever because it reduces ectopic fat and rapidly improves hepatic markers. But sustainable means compatible with real life and with adherence; it does not mean going to extremes. A reasonable framework includes: - adequate protein for satiety and muscle preservation; - fiber and low-energy-density foods; - reducing ultra-processed foods (not out of moralism, but because of density and hyper-palatability); - meal times consistent with sleep and routine (without turning timing into a religion).

As for movement: the combination of strength training and aerobic activity is generally more complete. The point is not to “burn”: it is that muscle contraction improves glucose uptake even through insulin-independent pathways and increases over time both glycogen storage capacity and oxidative capacity. Even walking regularly, especially after meals, can pragmatically change postprandial dynamics.

Weight loss often works—but it is not the only path. In some people, improvements also occur without major changes in body weight when body composition changes, when sedentary behavior is reduced, or when sleep is corrected. This matters because it shifts the focus from the scale to physiology.

Medications: there are clinical tools (metformin, GLP-1 agonists, and others) that may be appropriate in specific contexts. These are medical decisions, not “lifestyle choices.” They can be useful when risk and trajectory require it, or when lifestyle alone is not enough—but they do not replace work on the underlying determinants.

Supplements: Crionlab considers them secondary. In some profiles they may make sense: correcting a magnesium deficiency, increasing viscous fiber (e.g. psyllium) to modulate glycemic response and satiety, or using omega-3s in selected contexts as lipid/inflammatory support. But the response is variable, and the evidence does not justify promises. Even “antioxidant” compounds need to be properly placed: useful as contextual modulation, not as a shortcut—see, for example, Astaxanthin and protection from oxidative stress: what it can (and cannot) do in human physiology.

What promises too much: “resetting insulin,” detoxes, extreme eliminations, compulsive measurement, the narrative of total control. Even practices such as fasting, if presented as mythology, can create more fragility than benefit; it is worth reading a more sober framework here: Autophagy: how to activate it naturally (without fasting mythologies). Insulin sensitivity is a dynamic property: it improves with coherent signals over time, not with spikes of perfectionism.

In the end, the most useful question is not “how do I lower insulin?” but: what conditions am I creating every day—with movement, sleep, food, stress—that make it easier for the body to use energy without having to keep turning up the volume of the signal? When that coherence exists, physiology tends to become more readable again. And when it does not, the body is not “broken”: it is simply working in an environment that forces it into trade-offs.

FAQ

Is insulin resistance the same thing as type 2 diabetes?

No. Insulin resistance indicates a reduced tissue response to the insulin signal; type 2 diabetes is a clinical condition in which glycemic regulation becomes insufficient (because of a combination of resistance and pancreatic capacity that is no longer adequate). You can have insulin resistance for years with blood glucose still in the normal range, sustained by compensatory hyperinsulinemia.

Can you have insulin resistance with normal fasting glucose?

Yes. In the early stages, the body can maintain fasting glucose and HbA1c within range thanks to greater insulin secretion. In these cases, indirect clues may appear (elevated triglycerides, low HDL, fatty liver, increasing waist circumference), but the assessment needs to be integrated and discussed with a physician.

Do carbohydrates always cause insulin resistance?

No. Insulin resistance is more consistent with a problem of chronic energy load, sedentary behavior, ectopic/visceral fat, insufficient sleep, and circadian misalignment, in addition to individual predispositions. The quality of carbohydrates (fiber, food matrix) and the context (muscle activity, energy balance) matter more than the label “carbohydrates yes/no.”

How much does sleep matter compared to diet?

It matters substantially. Sleep restriction and irregular rhythms can worsen insulin sensitivity, increase appetite, and shift food choices toward more energy-dense foods. It does not replace nutrition, but it can amplify or sabotage dietary efforts.

Which tests are most useful for understanding the situation?

It depends on the clinical context. Fasting glucose and HbA1c describe blood glucose; fasting insulin and HOMA-IR can add information but have limitations; a lipid profile and signs of hepatic steatosis help clarify the overall metabolic picture. In some cases, an OGTT can clarify the postprandial response. The choice makes sense if guided by clinical history and risk factors.

Are there people who do not respond much to lifestyle interventions?

There is real variability. Genetics, age, body composition, degree of ectopic fat, medications, chronic stress, sleep disorders, and endocrine conditions can reduce or slow the response. This does not mean that it “doesn’t work,” but that more mature expectations, longer time frames, and sometimes clinical support are needed.

Can supplements “lower insulin” or solve insulin resistance?

In general, no, and that framing is misleading. Some supplements may be useful only as support in specific contexts (for example correcting a magnesium deficiency, increasing fiber with psyllium, or modulating certain lipid profiles with omega-3s), but they do not replace the main determinants: visceral/ectopic fat, muscle activity, sleep, and rhythmic consistency. The response is individual and should be assessed with caution.