Insulin sensitivity
How responsive your cells are to insulin, central to metabolic health.
Insulin sensitivity describes how readily your cells respond to insulin and take glucose out of the blood. When sensitivity is high, a small amount of insulin does the job. When it is low, which is insulin resistance, the pancreas has to shout to be heard, and insulin levels rise to keep blood glucose looking normal.
That last part is why it is worth understanding. Insulin resistance can run for years with a perfectly ordinary fasting glucose result, because the compensation is working. Blood sugar only drifts up when the pancreas can no longer keep pace, which is late in the story rather than early.
It matters because it sits upstream of type 2 diabetes, fatty liver and a good deal of cardiovascular risk, and because it is unusually responsive to behaviour. Few chronic processes shift as much on exercise and weight change as this one.
Exercise is the most reliable lever, and part of its effect does not depend on losing weight at all. Both aerobic and resistance training improve glucose disposal, with measurable effects after single sessions that accumulate with training. Muscle is the largest sink for glucose in the body, so having more of it and using it regularly changes where the glucose goes.
Weight loss is the most powerful lever when there is weight to lose, and the DiRECT trial is the clearest demonstration: a primary care weight management programme put 46% of participants into remission from type 2 diabetes at one year, against 4% in usual care, with mean weight loss of 10 kg. Remission tracked the amount lost, reaching 86% among those who lost 15 kg or more.
Measuring it outside a laboratory is imprecise. The reference method is a clamp study, which nobody is having done casually. In practice clinicians read fasting glucose, HbA1c and sometimes calculated indices such as HOMA-IR, the model published by Matthews and colleagues in 1985, which infers resistance from fasting glucose and insulin together. Waist measurement is the cheapest proxy of all, because visceral fat and insulin resistance travel together.
In practice: train regularly and keep the muscle you have, take the waist seriously, protect sleep, and treat a rising HbA1c as information rather than a verdict. Our metabolic fitness index and CGM metrics calculator both work from these numbers.
Sources
- Matthews DR, et al. Homeostasis model assessment: insulin resistance and beta-cell function from fasting plasma glucose and insulin concentrations in man. Diabetologia 1985;28:412-419
- Lean MEJ, et al. Primary care-led weight management for remission of type 2 diabetes (DiRECT): an open-label, cluster-randomised trial. Lancet 2018;391:541-551