Why your waist is probably bigger than you think

At Klarismo we are interested in body size and how it relates to people’s health and lifestyles. One of the measurements we give to our users is their waist circumference. This is a commonly used indicator of health, a significant factor in perceived attractiveness, and, you might think, useful for selecting well-fitting clothes so you can look your stylish best. However, it is actually a bit more complicated than that.

Of course, to learn anything from your waist measurement, it is important to first get an accurate figure for it. Self-reported waist circumferences by individuals tend to underestimate the values measured by healthcare professionals by around 3" on average, and so the health interpretations based on your own measurements may be highly inaccurate.

One explanation for the tendency to underestimate measurements may be misleading clothing sizes. Clothes which are labelled smaller than their actual size improve customers’ self-esteem and increase sales. This so-called “vanity sizing” is applied very inconsistently between manufacturers, with one study finding as much as 8" variation in a single size category of women’s clothing. If your Klarismo waist size is 2–3" greater than you expected based on your clothing size, this is the most likely explanation. Another important cause for confusion is that there can be a large discrepancy between the anatomical waist as defined by health professionals and researchers, and the level at which individuals prefer to wear the waist of their garments.

It turns out there is no single universally accepted position for performing waist measurements. Various definitions position it in the the region between the top of the pelvis and bottom of the ribs or relative to the navel, and each gives a slightly different result. Factors such as breathing state and time since last eating also introduce small variations, which limit accuracy to around 0.5".

At Klarismo we create a waist measurement from your MRI scan. However, the pelvis is difficult to locate directly using MRI, because bones don’t show up on a scan. Only the fat and water molecules in surrounding tissues create a signal. So as a workaround we base our waist measurement on the characteristic form of the lower back muscles at the top of the pelvis.

Top of the pelvis identified by the characteristic narrowing of the lower back muscles. The measured waist circumference is shown in green.

Waist size is very interesting from an evolutionary perspective. It influences the Volume Height Index (VHI), which research suggests is the most important visual cue for male attractiveness as judged by women. Body proportions associated with fitness also enhance male body attractiveness, such as a smaller waist in relation to the chest (the classic ‘inverted triangle’ shape) and hips, with an optimal Waist-To-Hip Ratio (WHR) of 0.8. For the attractiveness of women, VHI is again the most important factor, with an optimal WHR of 0.7. Of course, attractiveness is a huge benefit in natural selection, which implies that a low waist size is a sign of ‘fitness’ for survival.

Indeed, waist size is used as a proxy measure for abdominal obesity, and as such can tell us something about the risk of certain diseases. In fact, it can actually be used as a single risk factor for death due to any cause (cancer, cardiovascular disease, etc). This means the bigger your waist size, the more likely you are to die from any cause! Research shows that for men, the cause of death most strongly related to an increased waist size is that of respiratory diseases. Recommended ‘cut-off points’ to determine who may be at an increased risk are 40" for men and 35" for women. Again, you need to have an accurate measurement for this to be informative.

While waist measurement is useful as a rough gauge of health, a Klarismo scan can also give you more direct, objective and comprehensive measurements of body composition such as subcutaneous fat, visceral fat and muscle volumes.

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