ABSI (A Body Shape Index)

About ABSI (A Body Shape Index)

A Body Shape Index (ABSI) was developed by Nir Krakauer and Jesse Krakauer and published in 2012 in the journal PLoS ONE as an anthropometric index that isolates the harmful contribution of abdominal adiposity to mortality risk while being statistically independent of BMI. The Krakauers observed that waist circumference, BMI, and height are correlated, and they constructed ABSI so that it is uncorrelated with BMI by construction, allowing it to capture the residual risk associated with having more abdominal fat than expected for one's BMI.

How the formula works

ABSI = waist(m) / (BMI^(2/3) x height(m)^(1/2)). The waist is in meters and BMI in kg/m^2. The exponents 2/3 on BMI and 1/2 on height were chosen so that ABSI is uncorrelated with BMI, height, and weight in the NHANES population from which the formula was derived. The result is a dimensionless number, typically around 0.07 to 0.09 in adults, that expresses how much larger the waist is than would be expected for a person of the same BMI and height.

Evidence and mortality prediction

The Krakauers derived ABSI from NHANES data and validated it against the NHANES mortality follow-up, finding that ABSI predicted all-cause mortality more strongly than BMI or waist circumference alone. In their analysis, the highest ABSI quintile had roughly twice the mortality risk of the lowest, whereas BMI showed the familiar J-shaped association with weaker discrimination. Subsequent studies in multiple cohorts (including the British Regional Heart Study and the EPIC cohort) have largely confirmed that ABSI predicts mortality, cardiovascular disease, and diabetes independently of BMI, though the magnitude of improvement over waist circumference alone is modest. ABSI is best interpreted relative to age- and sex-specific population norms, often as a z-score or percentile, because the raw ABSI value varies systematically with age and sex.

Interpretation

Raw ABSI values average about 0.080 in adult men and 0.075 in adult women, rising with age. The interpretation bands used here are approximate; for individual risk assessment, ABSI should be compared to age- and sex-specific population distributions (typically from NHANES) to compute a z-score, which quantifies how far an individual's ABSI deviates from the population mean. A positive z-score (ABSI above the population mean) indicates higher-than-average mortality risk; a negative z-score indicates lower risk.

When to use it

ABSI is useful as a research and screening measure of abdominal adiposity that complements BMI by capturing risk that BMI misses. It is particularly informative for individuals with normal BMI but high waist circumference ('normal weight obesity'), in whom BMI would suggest low risk but ABSI correctly identifies elevated mortality risk. ABSI is also useful in epidemiological research as a mortality-predictive anthropometric index.

Limitations

ABSI's interpretation is less intuitive than waist circumference or waist-to-height ratio, and its risk bands depend on age and sex, which complicates clinical use. The raw ABSI value is difficult to interpret without reference to population norms, which limits its bedside utility. ABSI does not directly measure visceral fat (although it correlates with it), and its incremental predictive value over waist circumference alone is modest. The formula was derived in the U.S. NHANES population and may not generalize perfectly to other populations. Despite these limitations, ABSI is a valuable research tool and a useful complement to BMI for identifying abdominal-obesity-related risk.