Waists

The waist is the part of the torso between the bottom of the rib cage and the top of the hip bones. In common usage, the natural or true waist is the narrowest part of the torso, above the abdomen. Anatomically, the waist marks the transition between the thorax and the abdomen and is associated with the lumbar region of the spine. Fat distribution in this area varies among individuals and populations.

Waist measurements are used in health and nutrition contexts as an indicator of central or abdominal obesity. Clinically, waist circumference is typically measured around the abdomen at the end of a normal expiration, often at the level of the iliac crest. In fashion and anthropometry, the measurement may be taken at the natural waist, the narrowest part of the torso. Waist-to-hip ratio, calculated from waist and hip measurements, is another common indicator of fat distribution.

Health relevance and limits: A larger waist circumference and a higher waist-to-hip ratio are associated with increased risk of metabolic syndrome, cardiovascular disease, and type 2 diabetes, independent of overall body mass. Thresholds vary by guidelines and population; commonly cited cutoffs are about 102 cm (40 in) for men and 88 cm (35 in) for women for increased risk, with waist-to-hip ratio risk thresholds around 0.90 for men and 0.85 for women. However, waist measures are imperfect, as they do not distinguish fat from muscle and can be affected by breathing, posture, or recent food intake.

Cultural and practical uses: The waist is a key measure in clothing design and sizing, and it serves as a variable in anthropometric and epidemiological research.