In one sentence
Your waist divided by your hips, a measure of body shape: whether fat sits around the middle or lower down.
Why it matters
It is the older of the two ratios and the one most people have heard of. The World Health Organization's expert consultation set 0.90 for men and 0.85 for women as the points above which metabolic complications were substantially more common in the populations it reviewed (WHO 2011); those are published reference points, shown as such. The ratio has a weakness the height ratio does not: the hip is harder to measure the same way twice, and a ratio of two noisy numbers is noisier than either.
What moves it
Fat around the middle raises it; muscle and fat around the hips lower it; the tape technique at both sites moves it by a few hundredths.
How Vitality Tracker uses it
Part of the central-adiposity term in the Vitality Score's body-composition area, beside the waist-to-height ratio and the raw waist; displayed with the WHO reference points as context. The waist-to-height ratio is the one VT leans on.
How far to trust the number
As good as the two tape measurements, which means read it as a slow trend and never react to a single pair.
Sources
- World Health Organization. Waist circumference and waist–hip ratio: report of a WHO expert consultation, Geneva, 8–11 December 2008. WHO, 2011.