obesity: new definition vs BMI reveals better predictor of problems

 a European group redefined obesity, rejecting BMI as the standard, resulting in a very large number of people in the US being reclassified as obese (see obesity new defn not BMI JAMAopen2025 in dropbox, or doi:10.1001/jamanetworkopen.2025.37619). i will state in advance, and explain more later below, that to me this is clearly a valid and clinically important revision....

 

Background:

-- an international commission of 58 experts spanning multiple specialties and countries developed a new definition of obesity that incorporates some anthropometrics and/or direct measures of visceral body fat to better focus on this clinically important adipose tissue excess; these new guidelines achieved a 90 to 100% agreement within the committee and have already been endorsed by at least 76 professional organizations (see https://www.thelancet.com/journals/landia/article/PIIS2213-8587(24)00316-4/abstract ) in brief:

     -- obesity had been defined by BMI as a condition characterized by excess adiposity with or without abnormal distribution or function of adipose tissue

     -- clinical obesity was defined by this commission as a chronic, systemic illness characterized by alterations in the function of tissues, organs, the entire individual, or a combination of these, due to excess visceral adiposity

        -- clinical obesity can lead to severe a

end-organ damage causing life-altering and potentially life-threatening complications such as heart attack, stroke, and renal failure. of note, they also include limitations of daily activities associated with the effect of obesity on mobility and other activities of daily living (for example bathing, dressing, toileting, continents, and eating)

    -- preclinical obesity was defined as the state of excess adiposity with preserved function of other tissues and organs and with varying but generally increased risk of developing clinical obesity, as well as developing type II diabetes, cardiovascular disease, certain types of cancer, and mental disorders. The defining characteristic of preclinical obesity is its lack of associated clinical obesity complications

    -- BMI was recommended by the commission as a surrogate marker of health risk at a population level, for epidemiological studies, or for screening purposes, but not as an individual measure of health

--excess adiposity should be confirmed by direct measurement of body fat when available (eg, by optical scanning), or at least one anthropometric criterion (e.g. waist circumference, waist-to-hip ratio, or waist-to-height ratio) in addition to BMI, using appropriate cutoffs by age, gender, and ethnicity. However, people with the BMI > 40 can pragmatically be assumed to have obesity without further confirmation.

 

Details of the current study:

-- this study was developed to test the appropriate application of this new approach to obesity by accessing a large database, using the anthropometric definitions above, and assessing the validity of this new approach vs BMI

-- obesity was defined in this current study as:

    -- BMI-plus-anthropometric obesity: BMI above the traditional obesity threshold plus at least one elevated anthropometric measure, or BMI greater than 40

        -- the anthropometric evaluations were waist circumference, waist-to-hip ratio and waist-to-height ratio

    -- anthropometric-only obesity: BMI below the traditional obesity threshold plus at least 2 elevated anthropometric measures

    -- and obesity was categorized as clinical or preclinical based on the presence of organ dysfunction and/or physical limitation versus no evidence of these

 

-- this study applied the above definitions to the US-based All of Us (AoU) cohort to determine the prevalence of BMI-assessed obesity and clinical obesity under the new definition, including variations by age, sex and race/ethnicity; in addition, they planned to compare the characteristics of individuals who meet criteria for obesity based on elevated BMI plus anthropometric measures vs elevated anthropometric measures alone; and to evaluate longitudinal health outcomes across obesity subgroups as compared with individuals without obesity

    -- the AoU is an initiative of the NIH with "plans to enroll a diverse group of at least 1 million persons in the United States in order to accelerate biomedical research and improve health. The program aims to make the research results accessible to participants, and it is developing new approaches to generate, access, and make data broadly available to approved researchers. All of Us opened for enrollment in May 2018 and currently enrolls participants 18 years of age or older from a network of more than 340 recruitment sites. Elements of the program protocol include health questionnaires, electronic health records (EHRs), physical measurements, the use of digital health technology, and the collection and analysis of biospecimens. As of July 2019, more than 175,000 participants had contributed biospecimens. More than 80% of these participants are from groups that have been historically underrepresented in biomedical research": https://www.nejm.org/doi/full/10.1056/NEJMsr1809937.

    -- the current study included individuals to age 18-80 from this dataset, from individuals enrolled between May 31, 2017 and September 30, 2023, with median follow-up of 4.0 years

 

-- 301,026 individuals were included in this study:

    -- median age 54, 61% female, 53%white/20% Black/3% Asian/18% Latino, 57% never smoker/23% ever smoker/17% current smoker

    -- BMI 28.7, waist circumference 96.0 cm (elevated in 58.4%), hip circumference 106.7 cm and waist-to-hip ratio (elevated in 75.7%)

        -- the specific cutpoints used were not stated in the study, but the general cutpoints for obesity associated with substantially increased risk of metabolic complications, per the WHO definitions: https://iris.who.int/server/api/core/bitstreams/ca408ade-05c9-4b7c-8967-6ee5b5e0ccd8/content)

            -- waist circumference:

                -- men: 40 inches (102 cm), except in Asian men 37 inches (94cm)

                -- women: 35 inches (88cm), except in Asian women 31.5 inches (80cm)

            -- waist-to-hip ratio (with waist circumference measured at the narrowest point and hip circumference at the widest point):

                -- men: 0.90

                -- women: 0.85

 

-- classification by traditional BMI-obesity definition:

    -- obesity in 128,992 individuals (42.9%)

    -- no obesity in 172,034 individuals (57.1%)

-- 108,650 individuals (36.1%) had clinical obesity according to the new definition; 97,711 had preclinical obesity

    -- this prevalence of clinical obesity did increase with age: 24,498 of 45,018 individuals 70 years or older (54.4%) had clinical obesity

 

Main outcomes assessed: to compare the characteristics of individuals who met criteria for obesity based on elevated BMI plus anthropometric measures vs elevated anthropometric measures alone; and to evaluate longitudinal health outcomes across obesity subgroups as compared with individuals without obesity

Results:

-- obesity prevalence by type:

    -- traditional BMI: 128,992 individuals (42.9%)

    -- new definition: 206,361 individuals (68.6%)

        -- about a 60% increase by using the new definition, specifically related to adding only anthropometric criteria, as per graph below

    -- nearly all with the traditional BMI-only definition also met obesity criteria by the BMI-plus-anthropometric obesity definition

        -- only 678 participants (0.2%) no longer met criteria for obesity in the new classification due to high BMI but nonelevated anthropometric measures

    -- in contrast, 78,047 (25.9%) did not have obesity per the traditional measurement but were reclassified to having anthropometric-only obesity

    -- though overall obesity prevalence was similar between the sexes, there was a higher frequency of anthropometric-only obesity in males vs females (32.5% vs 21.7%), p<0.001

    -- the highest relative increase in obesity by the new definition was among Asian individuals (90.3% relative increase, from 27.0% to 51.4%)

    -- and, there was more prevalent obesity by the new definition in older people (43.9% in those 18-29yo vs 78.3% in those at least 70yo, p<0.001 for trend)

 

 

-- Differences in individuals with classical BMI- obesity vs anthropometric–only obesity, by subgroups (all comparisons were highly statistically significant):

    -- BMI vs anthropometric–only obesity: (median age 54 versus 60), male (34.7% versus 48.9%), higher education levels (35.2% versus 45%), and higher income (greater than $150,000 in 7.3% versus 12.5%)

    -- BMI vs anthropometric–only obesity: increased with age (26.9% aged 15-29 years versus 52.9% at least 70 years old)

    -- BMI vs anthropometric–only obesity:  BMI traditionally classified them as normal or underweight in 22.3%

     --Those with anthropometric-only obesity had all 3 anthropometric measures elevated in 48.5%; for those with BMI–plus–anthropometric obesity had all 3 in 71.9% 

 

-- Prevalence of clinical obesity by the new definition:

   --36.1% overall and 52.7% of those with traditional BMI-obesity had clinical obesity

        --This clinical obesity prevalence was comparable for the 2 sexes but increased with age, both in the overall cohort and among those with traditional BMI-obesity (in those 18-29 years old overall it was 8.5%, and for those who met criteria for clinical obesity it was 19.4%; for those at least 70 years old, these numbers respectively were 54.4% and 69.5%)

       --Clinical obesity was least common among Asian individuals (19.7% overall) and in 38.4% for those with obesity

        --Comparing traditional BMI categories:

            --Among 76,460 individuals with normal weight, 12.3% were classified as having preclinical obesity and 10.3% as clinical obesity under the new definition

            --Among 91,644 individuals who were overweight, 34.3% met the criteria for preclinical obesity and 31.9% for clinical obesity

 

-- comparison with no obesity:

    -- BMI-plus-anthropometric obesity: odds ratio for organ dysfunction 3.31 (3.24-3.37)

        -- per their supplementary eTable, the organ dysfunction definition of obesity is composed of higher levels of dysfunction in categories of: CNS, obstructive sleep apnea, hypoventilation, heart failure, atrial fibrillation (though with p=0.09 for AF), pulmonary hypertension, thrombosis, hypertension, metabolic, urinary, reproductive (male and female), musculoskeletal, lymphedema, physical limitation, and “any dysfunction”

 

--Comparison of clinical obesity phenotype with organ dysfunction: 

    --Comparing patients with BMI–plus–anthropometric obesity with anthropometric–only obesity: the former had a higher proportion of manifestations of organ dysfunction

        -- in a multivariable model adjusted for age, risk, and sex, the odds ratio of organ dysfunction for BMI–plus–anthropometric obesity versus anthropometric-only obesity favored the former, with ratios compared to those without obesity:

            -- BMI-plus-anthropometric obesity: Odds ratio 3.31 (3.24-3.37)

            -- anthropometric–only obesity: Odds ratio 1.76 (1.73-1.80)

            -- the most common manifestations of organ dysfunction associated with clinical obesity were hypertension, physical limitation, and obstructive sleep apnea

    --And, the frequency of organ dysfunction among people with obesity progressively increased with higher BMI among male and female participants with normal weight (47.8% and 43.9%, respectively) to overweight (50.4% and 46.0%, respectively) to obesity class I (54.7% and 48.5%, respectively), to obesity class II (63.0% and 55.3%, respectively), and to obesity class III (65.3% and 62.6%, respectively), all with a highly statistically significant trend, with p<0.001

 

 --Eligibility for obesity pharmacotherapy, excluding people with diabetes who might otherwise be GLP-1 receptor agonist therapy (defined as BMI>= 30, or between 27-30 with at least one obesity-related comorbidity):

    -- 111,467 individuals met criteria (44.7% of the whole cohort)

        --15,495 of 69,894 with clinical obesity (22.2%) by the new definition did NOT meet criteria for meds

        -- 57,068 (51.2%) of those eligible by BMI-based indications did NOT have clinical obesity by new definition

 

-- longitudinal health outcomes by obesity definition and phenotype

    -- comparing adjusted hazard ratios (aHRs) by traditional BMI and new definitions:

        -- incident diabetes vs no obesity:

             -- BMI: aHR 2.60 (2.50-2.70)

             -- new defn: aHR 3.21 (3.03-3.39)

                -- of new definitions: BMI-plus-anthropometric (conferred greatest risk): aHR 3.95 (3.73-4.18); anthropometric-only had aHR 2.12 (1.99-2.27)

        -- cardiovascular events vs no obesity:

             -- BMI: aHR 1.39 (1.34-1.45)

             -- new defn: aHR 1.70 (1.62-1.80)

                -- of new definitions: BMI-plus-anthropometric: aHR 1.81 (1.72-1.92); anthropometric-only had aHR 1.55 (1.46-1.65)

        -- all-cause mortality vs no obesity:

             -- BMI: aHR 1.10 (1.03-1.18)

             -- new defn: aHR 1.21 (1.12-1.31)

                -- of new definitions: BMI-plus-anthropometric: aHR 1.22 (1.12-1.34); anthropometric-only had aHR 1.20 (1.09-1.31)

[unfortunately, blogger will not print this figure, figure 3 in the article, which can be downloaded in full by opening doi:10.1001/jamanetworkopen.2025.37619]

 

-- longitudinal health outcomes by clinical obesity status, compared to individuals with no obesity or organ dysfunction

    -- incident diabetes:

        --overall for new defn: aHR 6.11 (5.67-6.60)

            -- preclinical obesity: aHR 3.32 (3.08-3.58)

            -- organ dysfunction in absence of diabetes: aHR 2.50 (2.25-2.78)

        -- cardiovascular events:

            -- overall for new defn: aHR 5.88 (5.38-6.43)

            -- preclinical obesity: aHR 1.40 (1.27-1.55)

        -- all-cause mortality:

            -- overall for new defn: aHR 2.71 (2.41-3.05)

            -- preclinical obesity: aHR 1.09 (0.96-1.25)  ie, no increased risk

    [my comment]:

         -- so, as with "prediabetes" vs diabetes, pre clinical obesity vs clinical obesity have 2 commonalities:

            -- both indicate a higher risk of developing into the full presentations of diabetes and clinical diabetes, respectively

            -- both are themselves associated with increased cardiovascular disease in their forme fruste presentations

 

 

 

 Commentary:

-- i do find it pretty shocking that 2 really old and consistently proven major cardiovascular risk factors are recycling to being important to understand and evaluate, many decades later (both have well-documented studies in the 1960's and '70s). one is obesity, where BMI has been used as the not-great surrogate marker vs visceral obesity as shown yet again above, and the other is lipoprotein (a), which has also been recognized as a really important marker of the lipid/atherosclerosis relationship (see https://gmodestmedblogs.blogspot.com/2025/06/high-lpa-increases-risk-of-recurrent.html ). 

-- the reason that visceral obesity is so important to me, is 2-fold:

    -- visceral obesity is the specific obesity associated with a high rate of systemic inflammation, and chronic systemic inflammation by whatever means seems to be associated with heart disease, diabetes, metabolic syndrome, cancer etc. Of importance, chronic inflammation is also associated with important, but not always acknowledged other conditions such as stress, depression, microparticle exposures, occupational exposures (firefighting, coal/steel industry, etc) and environmental (air pollution).  see https://gmodestmedblogs.blogspot.com/2023/10/update-ascvd-risk-factor-critique.html for some more details, though we can now add dysregulated aldosteronism to the mix: https://gmodestmedblogs.blogspot.com/2025/09/resistant-hypertension-are-diuretics.html). non-visceral obesity (eg "hour glass" vs "pear" shape) is not nearly as highly associated with chronic inflammation and the bad medical outcomes.

    -- and, this framing of obesity as being pro-inflammatory (visceral, as occurs more common in men) vs not (larger hips and buttocks, as is more common in women) is an important one since it correctly reflects the real underlying inflammatory mechanism for the associated adverse clinical events. I hope that reframing the visceral obesity issue in the context of systemic inflammation will increase our overall awareness of the importance of these multitude of issues associated with this inflammation

    -- visceral obesity is really easy to measure, not requiring a calculator as with BMI, with waist circumference being perhpas the best anthropometric indicator of visceral fat and the associated medical complications (eg, see https://pmc.ncbi.nlm.nih.gov/articles/PMC8967417/), though studies on this do vary. the gold standard is through imaging (eg 2- and 3-demensional optical scanning, though visceral fat can be seen in CT and MRI scans of the abdomen).  an argument against using BMI, see https://pmc.ncbi.nlm.nih.gov/articles/PMC11306271, commented that "BMI is not a direct measure of adiposity and cannot by itself be used to diagnose overweight or obesity. On an individual level, BMI lacks accuracy and reliability as an index reflecting adipose tissue mass. BMI overestimates adiposity in athletes with high muscle mass and in patients with edema, but underestimates adiposity in sarcopenic individuals with low lean mass." and the cutpoints for BMI vary in people from different countries. "the imprecision of BMI as a measure of adiposity weakens the association between BMI and cardiometabolic and other health risks and impairs its clinical use as a risk factor"

        -- for example, men from South Asia seem to have a higher rate of MIs at a younger age. one likely reason is that they are not necessarily obese by BMI but do have central (ie visceral) obesity: https://pmc.ncbi.nlm.nih.gov/articles/PMC2528919/ and https://www.heart.org/en/news/2023/05/17/why-are-south-asians-dying-of-heart-disease-masala-looks-for-answers

 

-- this current study of a large number of people from a diverse background found that 68.6% met criteria for clinical obesity, a pretty whopping 60% increase in obesity prevalence vs the current BMI-based definition

    -- and this was driven entirely by the inclusion of those individuals with anthropometric-only obesity (ie at least 2 elevated anthropometric measures) despite a nonelevated BMI in many

    -- however, almost all with elevated BMI still met criteria by the new framework of BMI-plus-anthropometric obesity (having at least on elevated anthropometric measure or BMI>40)

    -- this new definition effectively stratified individuals who were at high risk of organ dysfunction and long-term complications associated with obesity

        -- overall, about 1 in 4 people in this cohort met criteria for anthropometric-only diabetes; and about 1 in 4 who had normal BMI met criteria were at risk for incident diabetes, cardiovascular events and mortality

        -- and, of note per their definition above of needing pharmacologic intervention, 22.2% by the new definition did NOT meet criteria for meds (51.2% of those eligible by BMI-based indications did NOT have clinical obesity by new definition)

Limitations:

-- this is a retrospective but very large cohort study. as such, it cannot prove causality, only association (is it really the assessments used to assess adiposity, or is it unmeasured confounders??). for the more scientifically accurate assessment, there needs to be randomized controlled trials

    -- it would be great to know which of these different anthropometric assessments is best in order to find out which is the most useful to use clinically to predict future adverse outcomes (both morbidity and mortality)

-- in addition, it would be useful to have clear studies showing that decreasing visceral obesity leads to improvement in 

so, 

-- it has been clear from many studies over many decades that chronic systemic inflammation is associated with adverse metabolic effects, including heart disease, incident diabetes and all-cause mortality (as well as chronic kidney disease, some cancers, cognitive decline, and likely more)

-- it has also been clear that visceral obesity, and not non-visceral obesity, is associated with chronic systemic inflammation and all of these metabolic issues above (non-visceral obesity is minimally associated with chronic systemic inflammation in a few studies)

-- so, physiologically, there is no question that measuring visceral obesity is preferable to checking BMI, as is dramatically reinforced in the above study

    -- though, alas, this seems to have taken 50-60 or so years to resurface as the important issue it is...

-- there are still a few issues that need to be addressed:

    -- it would be very useful to know which specific anthropometric measure is the single best one we should use, and whether adding BMI to the mix, as above, provides additional benefit

    -- this should be evaluated in a prospective randomized controlled trial, with clear clinical endpoint results

    -- this should include a diverse population, best in several countries

    -- and, this really should be done soon, given the large number of people who have the remarkably high prevalence of diabetes, heart disease, kidney disease, other disabilities who might well benefit from this knowledge (visceral obesity is associated with insulin resistance: https://pmc.ncbi.nlm.nih.gov/articles/PMC11013274/ (a great article which goes into great detail on this, including that sugar-sweetened beverages, ultra-processed foods, high fructose diet, high saturated fat dietsk and poor nutrition overall all increase visceral adipose tissue)

    -- and, these anthropometric measurements are pretty easily implemented in outpatient settings, would change our clinical practice, and would be very likely to lead to huge clinical benefit for the population, especially since about 70% of the US population seems to have clinical obesity by this new definition....

geoff

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