As a GP, Dr Clare Bailey Mosley has supported hundreds of patients to lose weight, reduce their blood sugars and put their diabetes into remission. Still, one of the key tests she recommends doesn’t require a visit to the surgery or any specialist medical equipment. In an Instagram video with her son Dr Jack, she asks, ‘Did you know that the string test is a better measure of your metabolic health than BMI?’

Using a piece of string to measure your waist circumference, the two doctors explain, is a quick way to estimate your waist-to-height ratio, which NHS guidance suggests is a good indicator of your heart disease and type two diabetes risk.

‘The issue with BMI is that it doesn’t account for muscle mass but it also doesn’t account for your distribution of fat,’ explains Dr Jack Mosley. Short for ‘body mass index’, BMI is calculated by dividing your weight in kilograms by the square of your height in metres squared. Commonly used as a screening tool, it acts as a general guide to determine if your weight falls within a healthy range or if you are underweight, overweight or obese.

The problem? ‘One of the fats we’re most concerned about is your visceral fat,’ explains Jack. ‘This is the fat around your midriff, a fat that’s metabolically active, it clings to your organs and this is a fat that we’re more concerned about.’

Visceral fat releases harmful substances that trigger inflammation, disrupt hormones and damage arteries. So how can we keep an eye on our own levels? The Mosleys suggest this at-home method. Take a piece of string, use it to measure your height, then cut it to length. Once your string is the same length as you, cut it in half and wrap one half around your waist, just above your belly button. If the two ends fail to meet, says Clare: ‘It means that you are more likely to have metabolic issues like heading towards diabetes and being overweight.’

In fact, a high waist-to-height ratio has been linked to serious health conditions including heart disease, high blood pressure, type two diabetes, fatty liver disease and stroke. As Jack says, ‘It’s not about shaming anyone, but it is actually quite important.’ And if you’re worried by your results, your GP can always help you.