Step off the scale and grab a tape measure instead–your waist size is a great indicator of your current and future health. From FastExercise.
BMI is useful but it may not be the best predictor of future health. In a study of over 45,000 women followed for sixteen years, it was the waist-to-height ratio that proved a superior predictor of who would develop heart disease.
The reason the waist matters so much is because the worst sort of fat is visceral fat, which collects inside the abdomen. Most people think that fat is fat and all fat is equal. Recently it has become clear that this is not true. Subcutaneous fat, the sort of fat you get on your arms, legs, and buttocks, is unsightly but has relatively little impact on health. The visceral fat coats and infiltrates your internal organs like your liver and your pancreas. It causes inflammation and puts you at much higher risk of diabetes.
You would imagine that if you had lots of visceral fat you would have to look fat, but this is not the case. I only discovered that I was a TOFI (Thin on the Outside, Fat Inside) when I went for an MRI scan as part of a documentary. I didn’t look overweight but the scan revealed that in fact I had many liters of internal fat. Around 25% of people who have a normal BMI will have worrying levels of visceral fat, without knowing it. Although it is not ideal, if you can’t afford an MRI or a DXA scan, the simplest and cheapest test is a tape measure.
Male or female, your waist should be less than half your height. Most people underestimate their waist size by about two inches because they rely on trouser size. Instead, measure your waist by putting the tape measure around your belly button. Be honest. A definition of optimism is someone who steps on the scales while holding their breath. You are fooling no one.