Look Beyond BMI for Obesity Assessment

Body mass index (BMI) has been used to define obesity using only weight for height. However, it does not assess body fat and is therefore not a true reflection of obesity or health risk.

A higher weight may be due to increased muscle mass, which is generally associated with health, not disease. Conversely, a “normal BMI” may not reveal excess body fat associated with disease, especially fat carried around the waist. In fact, obesity and low muscle mass can coexist in a condition known as obesity-related sarcopenia.

Instead, measuring waist circumference, waist-to-hip ratio, or waist-to-height ratio provides a better ballpark estimate of obesity and associated disease risk. Body fat can be more directly measured using a DEXA scan [using X-ray radiation], two-dimensional MRI, and underwater weighing (hydrodensitometry).

A global committee of 58 medical experts, including those having experienced obesity, proposes objective criteria for diagnosing the disease of obesity and gauging its effects on health and disease risk (Rubino 2025):

• Obesity is characterized by excess fat mass (adiposity), with or without an abnormal distribution or function of adipose tissue, with underlying multifactorial causes
• Clinical obesity is a chronic, systemic disorder characterized by changes in tissue, organ, or whole-body function due to excess adipose tissue.
• Clinical obesity can lead to end-organ damage and life-changing and potentially life-threatening complications, including stroke, renal failure, and heart attack.
• Preclinical obesity is defined as excess adiposity but with preserved tissue and organ function. Preclinical obesity carries the risk of developing clinical obesity and other chronic disorders, including type 2 diabetes, cardiovascular disease, mental illness, and certain cancers.

Kyrou et al. 2018

Recommendations for clinical practice (Rubino 2025):

Clinical Assessment

People with confirmed excess adiposity should be assessed for clinical obesity. This assessment should include:

• A person’s medical history
• A physical examination
• Standard laboratory tests, including complete blood count, glycemia, lipid profile, and renal and liver function tests
• Additional diagnostic tests as appropriate if the patient’s medical history or physical examination, standard laboratory tests, or both suggest the possibility of one or more obesity-induced organ or tissue dysfunction

Goals of treatment in clinical obesity

• Improvement (or remission when possible) of the clinical manifestations of obesity
• Prevention of progression to further complications or end-organ damage

Desirable treatment outcomes (for practice and clinical trials)

• Objective improvement, remission, or both of clinical manifestations (rather than surrogate measures of risk or weight reduction per se)
• Plausibly, different clinical manifestations of clinical obesity (e.g., cardiovascular, metabolic, or musculoskeletal) might require a different intensity of treatment, respond to varying degrees of weight reduction, or both .

Interventions for clinical obesity (principles)

• The choice of intervention for clinical obesity (i.e., lifestyle, pharmacological, psychological, or surgical) should be based on:
• Individual risk-benefit assessment
• Available clinical evidence that the intervention has reasonable chances to improve clinical manifestations and quality of life or reduce the risk of disease progression and mortality

Optimal Takeaways

• BMI measurement should be used as an initial screening tool and accompanied by further evaluation of at least anthropometric criteria, e.g., waist circumference, waist-to-hip ratio, or waist-to-height ratio.
• Physical examination, medical history, and blood chemistry analysis should be incorporated into an obesity evaluation.
• Encourage regular aerobic exercise and weight training to promote an optimal body composition

References

Kuriyan, Rebecca. “Body composition techniques.” The Indian journal of medical research vol. 148,5 (2018): 648-658. doi:10.4103/ijmr.IJMR_1777_18 This is an open access journal, and articles are distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 License,

Kyrou, Ioannis, et al. “Clinical Problems Caused by Obesity.” Endotext, edited by Kenneth R Feingold et. al., MDText.com, Inc., 11 January 2018. This electronic version has been made freely available under a Creative Commons (CC-BY-NC-ND) license.  

NPR. Beyond BMI: Scientists propose a new way to define obesity : Shots - Health News Jan15 2025. https://www.npr.org/sections/shots-health-news/2025/01/15/nx-s1-5258427/bmi-obesity-definition-health 

Rubino, Francesco et al. “Definition and diagnostic criteria of clinical obesity.” The lancet. Diabetes & endocrinology, S2213-8587(24)00316-4. 9 Jan. 2025, doi:10.1016/S2213-8587(24)00316-4