ABSI, or A Body Shape Index, is a body-shape metric designed to estimate health risk linked with abdominal fat. Unlike BMI, which only uses height and weight, ABSI also includes waist circumference to better reflect central obesity.
What Is ABSI?
ABSI was developed by Nir Y. Krakauer and Jesse C. Krakauer in 2012. It helps measure whether your waist size is higher or lower than expected for your height and weight.
The main idea behind ABSI is simple: where fat is stored matters. Two people may have the same BMI, but the person with a larger waist may have a higher health risk because abdominal fat is more closely linked with metabolic and cardiovascular problems.
The ABSI Formula Explained
ABSI is calculated using waist circumference, BMI, and height. All values should be entered in SI units: metres and kilograms.
ABSI = Waist Circumference ÷ (BMI2/3 × Height1/2)
Where:
- Waist Circumference = measured in metres
- BMI = weight in kg ÷ height² in metres
- Height = measured in metres
ABSI Z-Score
The raw ABSI number is not easy to understand by itself. That is why an ABSI z-score is used. It compares your ABSI result with people of the same age group and sex.
Z-Score = (Your ABSI − Population Mean ABSI) ÷ Population Standard Deviation
ABSI Z-Score Risk Categories
| Z-Score Range | Risk Category | Approximate Percentile | Meaning |
|---|---|---|---|
| < -0.868 | Very Low | Bottom ~19% | Waist size is lower than expected for height and weight. |
| -0.868 to -0.272 | Low | 19th–39th | Below-average abdominal fat burden. |
| -0.272 to +0.229 | Average | 39th–59th | Typical abdominal fat level for age and sex. |
| +0.229 to +0.798 | High | 59th–78th | Higher abdominal fat than average. |
| > +0.798 | Very High | Top ~22% | Substantially elevated abdominal fat profile. |
NHANES Reference Values Table
The following ABSI reference values are based on NHANES population data and are used to estimate ABSI z-scores by age and sex.
| Age Group | Male Mean | Male SD | Female Mean | Female SD |
|---|---|---|---|---|
| 18–24 | 0.07530 | 0.00555 | 0.07440 | 0.00600 |
| 25–34 | 0.07660 | 0.00585 | 0.07580 | 0.00625 |
| 35–44 | 0.07800 | 0.00600 | 0.07730 | 0.00645 |
| 45–54 | 0.07920 | 0.00620 | 0.07890 | 0.00665 |
| 55–64 | 0.08030 | 0.00635 | 0.08020 | 0.00675 |
| 65–74 | 0.08110 | 0.00645 | 0.08120 | 0.00685 |
| 75–85 | 0.08160 | 0.00650 | 0.08200 | 0.00690 |
ABSI vs BMI vs WHtR vs WHR Comparison Table
| Index | What It Measures | Inputs Required | Age/Sex Adjusted? | Main Limitation |
|---|---|---|---|---|
| BMI | Body weight relative to height | Weight, height | No | Cannot show fat distribution or muscle mass. |
| ABSI | Waist size adjusted for BMI and height | Weight, height, waist, age, sex | Yes | Less familiar and less intuitive than BMI. |
| WHtR | Waist size compared with height | Waist, height | No | Simple but does not adjust for weight. |
| WHR | Waist size compared with hip size | Waist, hip | Partly | Requires accurate hip measurement. |
Proper Waist Measurement Guide With Steps
Accurate waist measurement is very important because ABSI depends heavily on waist circumference.
- Stand straight with your feet shoulder-width apart.
- Use a flexible measuring tape.
- Find the midpoint between the bottom of your ribs and the top of your hip bone.
- Wrap the tape around your waist at this level.
- Keep the tape snug but not tight.
- Breathe out normally before taking the measurement.
- Record the value in centimetres or inches, then convert if needed.
Avoid measuring over thick clothing, pulling the tape too tightly, or holding your breath.
Age-Specific Risk Discussion
ABSI risk should be interpreted with age in mind. Waist circumference and body composition often change as people get older. For example, muscle mass may decrease while abdominal fat may increase, even if body weight remains stable.
This is why ABSI uses age-specific reference values. A raw ABSI score that looks high for a younger adult may have a different interpretation in an older age group. The z-score gives a more balanced comparison by checking your result against people of similar age and sex.
Visceral Fat Science Section
Visceral fat is the fat stored deep inside the abdomen around internal organs such as the liver, pancreas, and intestines. It is different from subcutaneous fat, which sits under the skin.
Higher visceral fat is associated with increased inflammation, insulin resistance, abnormal blood lipids, fatty liver risk, and higher cardiovascular risk. ABSI does not directly measure visceral fat like a CT or MRI scan, but a higher waist circumference relative to body size can be a useful indirect signal of excess central fat.
Limitations of ABSI
ABSI is useful, but it is not perfect. It should not be treated as a medical diagnosis.
- It estimates risk; it does not directly measure body fat.
- It depends on accurate waist measurement.
- It may not perform equally well in every ethnicity or population.
- It does not consider fitness level, muscle mass, diet, smoking, blood pressure, or blood tests.
- It should be used with BMI, waist-to-height ratio, and clinical advice where needed.
Important: A high ABSI score does not automatically mean you have a disease. It means your abdominal body shape may be associated with higher health risk and may be worth discussing with a healthcare professional.
How to Use ABSI Correctly
Use ABSI as a complementary tool. BMI can show whether body weight is generally low, normal, overweight, or obese. ABSI adds another layer by showing whether waist size is higher than expected for your height and weight.
If BMI is normal but ABSI is high, it may suggest hidden abdominal fat risk. If BMI is high but ABSI is average, the risk pattern may be different. For best interpretation, consider ABSI together with waist circumference, blood pressure, cholesterol, glucose levels, physical activity, and medical history.
Complete FAQ
What does ABSI stand for?
ABSI stands for A Body Shape Index.
Is ABSI better than BMI?
ABSI is not a full replacement for BMI. BMI measures general body mass, while ABSI focuses more on abdominal body shape and central fat risk.
What is a good ABSI z-score?
An average ABSI z-score is between -0.272 and +0.229. Lower scores usually suggest lower abdominal-fat-related risk, while higher scores suggest increased risk.
Why does waist size matter?
Waist size matters because abdominal fat, especially visceral fat, is more strongly linked with metabolic and cardiovascular health risks than fat stored in some other areas.
Can ABSI diagnose obesity?
No. ABSI is a risk indicator, not a diagnosis. It should be used as a screening or educational tool.
Can ABSI be high if BMI is normal?
Yes. A person can have a normal BMI but a high waist circumference for their body size. ABSI is designed to identify this pattern.
Can athletes have misleading ABSI results?
Possibly. Athletes or people with unusual body composition may need more detailed assessment because simple formulas cannot fully separate muscle, fat, and body frame differences.
How often should I check ABSI?
You can check it every few months if you are tracking weight, waist size, or lifestyle changes. Daily measurement is unnecessary.
Does ABSI work for children?
ABSI is mainly used for adults. Children and teenagers need age-specific growth charts and pediatric assessment.
Should I see a doctor for a high ABSI score?
If your ABSI score is high or very high, especially along with high blood pressure, high blood sugar, abnormal cholesterol, or family history of disease, it is a good idea to speak with a healthcare professional.
Final Thoughts
ABSI is a helpful tool for understanding abdominal body shape and possible health risk. It works best when used alongside BMI, waist measurement, lifestyle factors, and medical guidance. A high ABSI score should be seen as a signal to review your health, not as a final diagnosis.