Body Roundness Index (BRI) Explained: A Newer Body-Shape Metric and What It Predicts

Body Mass Index has been the default body-composition number for forty years, and a lot of its limitations are well known. Two people with the same BMI can carry very different amounts of fat in very different places. A muscular athlete and a sedentary adult with no muscle can land at the same BMI category. And BMI tells you nothing about where body fat is — which matters, because the fat carried around the abdomen carries a different metabolic risk profile than fat distributed elsewhere.

Body Roundness Index, or BRI, was developed in 2013 to address part of that gap. It uses only two measurements — your height and your waist circumference — and produces a single number that estimates your body shape on a roughly 1-to-15 scale. The math behind it treats the body as an ellipse and asks how round versus cylindrical that ellipse is. A round shape (more abdominal fat, larger waist relative to height) produces a higher BRI; a more cylindrical shape produces a lower BRI.

If you want to see your own number first, our Body Roundness Index calculator takes height and waist circumference and returns your BRI with the appropriate risk band. Then come back here for what the score actually means and how the research has evolved since 2024.

How BRI Differs From BMI

BMI and BRI both produce a single number, but they ask different questions. BMI asks how heavy are you for your height? BRI asks how round is your body shape relative to your height?

The practical implication: BMI can miss central adiposity entirely. A person whose weight has shifted toward the abdomen as they age may keep the same BMI for years while their visceral fat — the metabolically active fat surrounding internal organs — quietly increases. BRI captures that change because it uses waist circumference, which scales directly with abdominal fat distribution.

BRI is also closely related to waist-to-height ratio (WHtR), which has been studied for decades. The math behind BRI is essentially a reformulation of WHtR into an ellipse-based geometry, with the result rescaled to a 1–15 range. Many of the findings about WHtR — that it predicts cardiometabolic risk better than BMI alone, that a ratio above 0.5 is a useful screening threshold — apply, in spirit, to BRI as well. If you've already used our waist-to-height ratio calculator, BRI is the same underlying signal expressed differently.

What the 2024 JAMA Study Found

The most influential BRI study to date was published in JAMA Network Open in 2024. Researchers analyzed data from 32,995 US adults across nearly two decades of NHANES (the National Health and Nutrition Examination Survey) and connected each participant's BRI to subsequent all-cause mortality records. Two findings stood out.

First, the average BRI in US adults rose from 4.80 to 5.62 between 1999 and 2018 — a ~17% increase that tracks the broader rise in central adiposity in the US population over the same period. The trend was visible across age groups and both sexes.

Second, the relationship between BRI and all-cause mortality was U-shaped, not linear. Adults with mid-range BRI (around 5) had the lowest mortality. Risk rose meaningfully at higher BRI — adults with BRI of 6.9 or above had an all-cause mortality risk that was up to 49% higher than the mid-range group. Risk also rose at the very low end of the BRI distribution, which the authors interpreted as reflecting underlying conditions associated with low body weight (frailty, undiagnosed disease, advanced age) rather than BRI itself causing harm.

The U-shape is the part that often gets lost in coverage. "Lower BRI is healthier" is wrong as a blanket statement. What the data supports is closer to: extreme values in either direction warrant attention, and the safest band sits in the middle.

What the Follow-Up Research Adds

Since the 2024 paper, several independent cohorts have tested whether the same pattern holds in different populations.

• Older US adults (Scientific Reports, 2025): A prospective analysis of older NHANES participants confirmed the U-shaped relationship between BRI and all-cause mortality, with both ends of the BRI distribution associated with elevated risk versus the middle.
• Japanese adults + meta-analysis (PubMed PMID 41022153, 2025): A study in Japanese adults plus a preliminary meta-analysis of available cohorts replicated the BRI-mortality association across populations with different baseline body-shape distributions.
• Chinese national cohort (PMC12748138, 2026): A national prospective longitudinal study in Chinese adults examined BRI and mortality in people with chronic diseases. The U-shape was again present, with associations persisting across cardiovascular disease, diabetes, and chronic kidney disease subgroups.
• Older Chinese cohort (Frontiers in Public Health, 2023): An earlier cohort in middle-aged and older Chinese adults found that not only baseline BRI but also BRI trajectory over time predicted all-cause and cardiovascular mortality — adults whose BRI rose steeply over the follow-up period had higher mortality than those whose BRI stayed stable.

Across these studies, the consistent pattern is association, not proof of causation. BRI captures something about body shape that correlates with metabolic and cardiovascular risk. The mechanisms are well established for the underlying biology — visceral fat secretes inflammatory adipokines, alters glucose and lipid handling, and is mechanically associated with hepatic steatosis — but BRI itself is a measurement, not a treatment target. Lowering BRI through unhealthy means (severe undereating, untreated illness) does not lower the risk it screens for.

Reading Your BRI Score

The BRI calculator on this site uses risk bands grounded in Thomas et al. (2013) and the more recent population studies above. A general guide:

• BRI under 1.0 — Very Lean: May indicate insufficient body fat reserves, which carries its own health considerations — particularly in older adults, where low BRI has been linked to elevated mortality risk.
• BRI 1.0 to 3.4 — Healthy: Aligned with lower mortality hazard ratios in the population studies. Maintain habits that support stable body composition.
• BRI 3.4 to 4.5 — Average: Within typical population range, but in the upper half of recent NHANES distributions. Worth watching alongside other indicators.
• BRI 4.5 to 5.5 — Above Average: Approaching the threshold where central adiposity contributes meaningfully to cardiometabolic risk. Consider discussing waist trends and cardiometabolic markers with your provider.
• BRI above 5.5 — Elevated: The 2024 JAMA study showed mortality risk climbing meaningfully past this point, with a ~49% relative increase at BRI 6.9 and above. A conversation with a healthcare provider about cardiometabolic screening, lifestyle factors, and personalized targets is appropriate.

BRI is most informative when read in context — alongside BMI, waist-to-hip ratio, blood pressure, fasting glucose or HbA1c, and lipid panel. Any single number is a screening signal, not a diagnosis.

How to Measure Waist Circumference Accurately

BRI is sensitive to waist measurement, so the precision of your input matters. The standard protocol used in the NHANES surveys (and reflected in our calculator):

• Measure in the morning, before eating, in light clothing.
• Find the top of the hip bone (iliac crest) and the bottom of the rib cage. Measure at the midpoint between them — typically near or just above the navel.
• Stand relaxed with arms at sides. Don't suck in. Don't push out.
• Use a flexible (not stretchy) measuring tape, snug against the skin without compressing it.
• Take two measurements and average them. If they differ by more than 1 cm, take a third.

Common errors that distort BRI: measuring at the narrowest point (which underestimates abdominal fat in many adults), measuring after a large meal (post-prandial bloat can add several cm), or measuring over heavy clothing.

What BRI Does Not Tell You

BRI is a body-shape estimate from two measurements. There are several things it specifically does not measure:

• Body fat percentage. BRI estimates shape, not composition. Two people with the same BRI can have different body fat percentages. Our body-fat calculator and the body-fat methods comparison guide cover this directly.
• Muscle mass. BRI does not distinguish between visceral fat and abdominal muscle thickness. People who carry significant abdominal muscle (some athletes) can have a higher BRI than their cardiometabolic risk profile would predict.
• Cardiovascular fitness. Cardiorespiratory fitness is an independent — and arguably stronger — predictor of mortality than any body-shape metric. See our VO₂ max guide for context.
• Trajectory. A single BRI measurement misses whether your body shape has been stable, improving, or worsening over time. The Frontiers 2023 cohort highlighted that change in BRI may matter as much as the baseline value.

Putting BRI in Context

If your BRI is in the elevated range, the practical next step is not to optimize the BRI number itself. It is to ask the underlying question that BRI was built to flag: how much abdominal fat are you carrying, and what cardiometabolic markers might it be affecting? That conversation looks at fasting glucose, HbA1c, lipid panel, blood pressure, and family history — alongside body-shape measurements — and is the kind of conversation worth having with a healthcare provider.

For self-tracking, BRI works best as one signal in a small panel: body-shape (BRI or waist-to-height ratio), weight (BMI as a coarse trend indicator), and a fitness measure (VO₂ max or step count). Watching all three over time gives a more complete picture than any one of them alone.

The bottom line: BRI is a useful refinement on top of BMI for adults who want a body-shape number that captures abdominal distribution. The 2024 JAMA Network Open study and its 2025–2026 replications make a credible case that BRI carries information about cardiometabolic and mortality risk beyond what BMI alone provides. Read your score in context, don't optimize it in isolation, and use it as a prompt for the broader conversation about cardiometabolic health rather than the answer.