To understand insulin resistance, start with what insulin normally does.
After you eat, blood sugar rises. The pancreas releases insulin in response. Insulin acts as a key - it binds to receptors on muscle, liver, and fat cells, unlocking them so glucose can enter and be used for energy or stored. Blood sugar falls back to normal. That's the healthy cycle.
Insulin resistance is when the locks stop working properly. Cells become less responsive to insulin's signal. To get the same job done, the pancreas produces more and more insulin. For a while, it works - blood sugar stays controlled but insulin levels run chronically high. Eventually, the pancreas can't keep up, blood sugar rises, and you have type 2 diabetes.
How Insulin Resistance Develops
It's not a switch that flips suddenly. It's a gradual process, typically driven by a combination of:
Excess visceral fat. Fat stored around the abdominal organs (visceral fat, as opposed to subcutaneous fat under the skin) releases inflammatory cytokines and free fatty acids that directly interfere with insulin receptor signalling. This is the strongest driver of insulin resistance in most people. Waist circumference is a more reliable risk marker than total body weight.
Chronic high refined carbohydrate intake. Regularly eating foods that spike blood sugar keeps the body in a state of high insulin demand. Over time, cells downregulate their insulin receptors in response to constant high insulin exposure - the same mechanism through which drug tolerance develops.
Physical inactivity. Muscle is the body's primary site of glucose disposal. Active muscle is significantly more insulin-sensitive than inactive muscle. Sedentary behaviour reduces muscle's ability to take up glucose efficiently, pushing more of the burden onto the liver and pancreas.
Chronic inflammation. Inflammatory cytokines - particularly TNF-alpha and interleukin-6 - directly impair insulin receptor signalling. People with chronic low-grade inflammation have measurably worse insulin sensitivity.
Poor sleep and chronic stress. Both raise cortisol. Cortisol is inherently glucose-raising - it's a counter-regulatory hormone designed to increase blood sugar in emergency situations. Chronic cortisol elevation chronically disrupts blood sugar regulation.
Signs That May Indicate Insulin Resistance
Insulin resistance is often symptom-free in early stages - it develops silently for years. Some signs that can point to it:
- Difficulty losing weight despite reasonable calorie restriction
- Energy crashes after carbohydrate-heavy meals
- Persistent hunger within 2 hours of eating
- Fat accumulation around the abdomen specifically
- Skin tags (acrochordia) - small flesh-coloured growths in skin folds
- Acanthosis nigricans - darkened skin patches in neck creases, armpits, or groin
- High triglycerides and low HDL cholesterol on a blood panel
A fasting insulin blood test is the most direct measure. Standard blood glucose tests can appear normal even when insulin resistance is already significant, because insulin is working overtime to keep glucose controlled.
How to Improve Insulin Sensitivity
The good news: insulin resistance is largely reversible in its early stages through diet and lifestyle changes.
Reduce refined carbohydrate and added sugar intake. This directly reduces chronic insulin demand and gives receptors a chance to recover sensitivity.
Increase dietary fibre. Fibre slows glucose absorption, reducing the amplitude of blood sugar spikes. Aim for 30g daily from varied sources. See the guide to dietary fibre for practical sources.
Exercise - particularly resistance training. Skeletal muscle can absorb glucose without insulin during exercise (through a separate GLUT4 pathway). Building muscle mass increases the body's total glucose disposal capacity. Even a single 30-minute resistance training session improves insulin sensitivity for 24-48 hours.
Lose visceral fat. Even modest weight loss (5-10% of body weight in people who are overweight) produces measurable improvements in insulin sensitivity. The priority is visceral fat reduction, which responds well to diet and exercise.
Improve sleep. A single night of inadequate sleep measurably reduces insulin sensitivity the following day. Consistently poor sleep is one of the more underappreciated drivers of metabolic dysfunction.