Insulin resistance
Insulin resistance: cells respond poorly to insulin, so the body makes more and more of it. Often a silent precursor to type 2 diabetes – and very much something you can influence.
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Insulin is the key that lets sugar out of the blood and into the cells. With insulin resistance, the lock sticks: muscle, liver and fat cells respond less strongly, and the pancreas has to release more and more insulin to keep blood sugar normal. It manages this for years – blood sugar looks unremarkable, but insulin levels keep rising.
That's exactly what makes insulin resistance so insidious: it causes no symptoms and barely shows up in standard blood tests. Clues include a larger waist, high triglycerides, low HDL and, in teenagers, sometimes a velvety, dark discolouration of the skin in the folds of the neck or armpits (acanthosis nigricans). It can be estimated using the HOMA index, calculated from fasting insulin and fasting blood sugar – but this isn't a routine test, and there are no fixed cut-off values.
The drivers are fat around the abdomen and in the liver, lack of exercise, lack of sleep, chronic stress and genetic predisposition. Visceral fat releases fatty acids and inflammatory messengers that interfere with insulin signalling in the cells. High insulin levels also slow down the release of fat from fat cells. Losing weight still works with a moderate calorie deficit – it can just feel like harder going, and that's not down to a lack of willpower.
Your muscles are the biggest lever: they take up most of the sugar after a meal, and even a single workout increases insulin sensitivity for around 24 to 48 hours. Strength training builds muscle and so enlarges your sugar store, as long as you keep at it. Add to that fibre and protein at every meal, fewer sugary drinks, seven to nine hours of sleep for adults and a moderate calorie deficit – losing 5 to 10% of your weight significantly improves insulin action.
In women, polycystic ovary syndrome (PCOS) is closely linked to insulin resistance; here too, exercise is part of the treatment. Children who are very overweight and have dark skin folds should be seen by a paediatrician – not to be put on a diet, but to have their values checked.