A Body Shape Index (ABSI) Calculator

What Is ABSI?

A Body Shape Index (ABSI) is a measure of abdominal obesity introduced in 2012 by Nir Y. Krakauer and Jesse C. Krakauer in a study published in PLoS ONE. It was developed to quantify the risk associated with abdominal obesity, where obesity is indicated by a wide waist circumference relative to a person's height and body mass index (BMI).

Medical exam and mortality data were analyzed on a sample of more than 14,000 adults from the United States National Health and Nutrition Examination Survey (NHANES) 1999–2004. The researchers found that an above-average ABSI was associated with a substantially higher risk of death, and that the excess mortality hazard associated with high ABSI was greater than that associated with above-average BMI or waist circumference alone.

The study concluded that even with a normal BMI, you may be at greater risk of dying sooner if you carry excessive weight in your midsection relative to your height and weight.

The ABSI Formula

ABSI is computed from waist circumference (WC), weight, and height in SI units:

The exponents on weight and height are chosen so that ABSI is approximately independent of weight and height in the reference population. This means a high ABSI specifically reflects waist circumference being larger than expected for a given body size, rather than just overall body mass.

Why Waist Circumference Matters More Than Weight Alone

Waist circumference directly measures abdominal fat, particularly visceral fat surrounding internal organs. This type of fat is strongly associated with an increased risk of cardiovascular disease, type 2 diabetes, and premature death. While weight and BMI provide an overall assessment of body mass, they do not differentiate between muscle, bone, and fat, nor do they indicate where fat is stored.

When waist circumference is combined with BMI, the ability to identify individuals at high risk for serious health problems improves significantly. Studies show that after adjusting for BMI, higher waist circumference is consistently associated with greater risk of morbidity and mortality, even among people with normal BMI. This is because waist circumference better reflects the accumulation of harmful visceral fat, which is metabolically active and contributes to insulin resistance and inflammation.

How ABSI Improves on Traditional Indices

ABSI focuses specifically on waist circumference in relation to body size and mass rather than relying solely on overall weight or BMI. Unlike BMI, which is simply weight divided by height squared, ABSI adjusts waist circumference for what would be expected based on a person's height and weight rather than just using the raw measurement.

By doing this, ABSI provides a measure of abdominal obesity that is largely independent of overall body size. A high ABSI indicates that a person's waist circumference is larger than expected for their height and weight, suggesting a more central concentration of body mass and potentially higher visceral fat. This independence enables ABSI to identify individuals at increased risk for health problems associated with abdominal obesity, even if their overall weight or BMI falls within normal ranges.

Other indices, such as BMI or simple waist circumference, are more directly influenced by height and/or weight, making it harder to distinguish individuals with high muscle mass or generalized fat accumulation from those with dangerous abdominal fat accumulation. ABSI provides a more precise assessment of abdominal obesity risk that's independent of height and weight.

How to Measure Waist Circumference

Accurate waist measurement is essential for a meaningful ABSI score. Use the following guidelines:

Interpreting Your ABSI z-Score

Your ABSI value alone has little intuitive meaning, so the calculator converts it into a z-score by comparing against population norms for your age and sex (smoothed from NHANES 1999–2004 data). The z-score indicates how many standard deviations your ABSI sits above or below the average for your demographic group.

The z-score is then mapped into one of five risk categories:

Mortality Risk Estimates

For ages 16 and over, the calculator also reports a relative mortality hazard ratio. This compares your projected all-cause mortality risk to the population average at your ABSI percentile, derived from the original Krakauer & Krakauer hazard tables. A hazard ratio of 1.00 corresponds to average risk; values above 1.00 indicate elevated risk and values below 1.00 indicate reduced risk relative to the population mean.

For example, a hazard ratio of 1.20 means your relative mortality risk from waist circumference alone is roughly 20% higher than someone of your age and sex with average ABSI. These estimates are derived from the NHANES 1999–2004 cohort and should be interpreted as broad statistical comparisons, not individualized predictions.

Comparisons of Anthropometric Indices

A 2020 study by Christakoudi et al. examined a large European cohort to compare the usefulness of various body shape indices in assessing obesity-related mortality risk. The study evaluated waist-circumference-based indices including ABSI, the Body Roundness Index (BRI), Waist-to-Hip Ratio (WHR), Waist-to-Height Ratio (WHtR), the Weight-adjusted Waist Index (WWI), and others.

The researchers found that ABSI provides a more accurate assessment of mortality risk than alternative measures. Because ABSI is designed to be independent of BMI, it works well alongside BMI and helps effectively categorize risk for underweight, overweight, obese, and average-weight individuals.

Reducing Abdominal Fat

There are no proven methods for spot-reducing abdominal fat. Exercising specific muscle groups or following a particular diet won't selectively trim your waist. However, several scientifically supported approaches help reduce overall body fat, including abdominal fat:

Increase soluble fiber intake. Foods rich in soluble fiber (fruits, vegetables, legumes, oats, barley) help you feel full longer and may reduce belly fat gain over time.

Reduce refined carbs and sugars. Limiting refined carbohydrates and sugar-sweetened beverages is linked to less abdominal fat accumulation. A Johns Hopkins study found that, for the same calorie intake, low-carb dieters lost more weight than low-fat dieters, with comparable preservation of lean tissue, meaning a higher proportion of fat loss.

Avoid trans fats. Trans fats, often found in processed foods, are associated with increased abdominal fat and should be avoided.

Choose healthy fats. Replacing unhealthy fats with sources like avocados, nuts, seeds, and fatty fish can support overall fat loss.

Mediterranean-style eating. Evidence supports that following a Mediterranean diet can help reduce abdominal fat and improve cardiometabolic health.

Aerobic exercise. Regular aerobic activity such as brisk walking, running, or cycling is effective at reducing overall body fat, including abdominal fat. A French research team's review of 149 high-quality studies found that aerobic exercise, alone or combined with resistance training, produced meaningful reductions in visceral fat. Resistance exercise alone showed limited effect on visceral fat specifically.

Resistance training. Strength exercises help build muscle, which raises resting metabolism and supports fat loss alongside other interventions.

High-Intensity Interval Training (HIIT). HIIT workouts are time-efficient for burning calories and reducing body fat.

Daily movement, sleep, and stress. Adding incidental activity, prioritizing sleep, and managing stress (which elevates cortisol and promotes abdominal fat storage) all contribute to reducing visceral fat over time.

Frequently Asked Questions about ABSI

Caution: This calculator is intended for illustrative and educational purposes only, and is not for medical use. ABSI is designed to be used together with the more familiar body mass index (BMI), not as a replacement.

Further Reading:

1. The original ABSI study by N.Y. Krakauer and J.C. Krakauer, published in PLoS ONE (2012), introduced ABSI as a measure of abdominal obesity that predicts mortality hazard independently of BMI, based on analysis of NHANES 1999–2004 data on roughly 14,000 adults. View study
2. A follow-up paper by Krakauer and Krakauer in PLoS ONE (2014) extended the original work by examining how changes in ABSI over time relate to mortality hazard, providing the longitudinal validation that underpins this calculator's risk estimates. View study
3. A 2020 study by S. Christakoudi and colleagues, published in Scientific Reports, compared ABSI against alternative abdominal obesity indices in a large European cohort and concluded that ABSI achieves better mortality risk stratification than competing measures. View study
4. A 2024 study by X. Zhang and colleagues, published in JAMA Network Open, examined the Body Roundness Index (BRI) and its association with all-cause mortality among US adults, offering useful context for how ABSI compares to other shape-based indices. View study
5. The U.S. Centers for Disease Control and Prevention publishes the National Health and Nutrition Examination Survey (NHANES) data tables that provide the population reference values used by ABSI's normative tables. View resource