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Why BMI is Misleading: The Truth About Weight, Obesity, and Fitness

ABSTRACT

The Body Mass Index (BMI) is widely used in healthcare to assess health and fitness by measuring weight-to-height ratio. However, its global reliance has faced criticism for contributing to weight stigma and oversimplifying health assessments. Critics argue that the status of health and fitness is more complex than numbers on the BMI scale, and cannot be fully understood using only weight and height. This study reviews recent research on the credibility of BMI, evaluating its benefits and limitations and proposes best practices to optimize its use without perpetuating stigma.

© 2024 The Authors. Hosting by Atomic Academia Ltd. Licensed under CC BY 4.0.

1. Introduction and Objectives


Since the 1830s, the Body Mass Index (BMI) has been used as a standardized metric for assessing health status globally. Originally developed to study average body types among white Europeans, it was not intended to serve as a primary indicator of health. However, due to its simplicity and affordability, BMI has become a cornerstone of healthcare practices worldwide1​. By calculating weight-to-height ratios, BMI simplifies health and fitness levels 1-3​. BMI categorizes individuals as underweight, normal, overweight, and obese 1,2​ (Figure 1) with ideal ranges typically defined as 18.5–25.0 kg/m².
The widespread use of BMI has helped simplify healthcare assessments and promote awareness of obesity as a risk factor for several chronic and life-threatening diseases, including diabetes, cardiovascular conditions, hypertension, and certain cancers 1,2,4-8​. Healthcare practitioners often use BMI as a guiding metric for recommending lifestyle changes or interventions. However, this reliance has led to criticism, as BMI fails to account for variations in body composition, genetics, and other factors influencing health. Consequently, individuals whose BMI falls outside the ideal range are often subject to drastic lifestyle recommendations that may not align with their overall health status. Critics argue that diagnosing complex health conditions based solely on weight-to-height ratios is overly simplistic and potentially harmful. For example, BMI does not differentiate between muscle mass and fat, leading to misclassifications, such as labeling muscular individuals as obese. Furthermore, BMI's historical origins and its failure to account for diversity across populations raise questions about its relevance in modern healthcare. This research seeks to evaluate the credibility of BMI as a primary health and fitness indicator by analyzing its strengths and limitations. It also aims to identify a balanced approach, recognizing the utility of BMI while mitigating the harm caused by over-reliance. By exploring recent studies and best practices, this work endeavors to provide a nuanced perspective on how BMI can be integrated into healthcare in a more effective and equitable manner.

Figure 1 - BMI categories: Underweight, Normal, Overweight, and Obese
Figure 1 - BMI categories: Underweight, Normal, Overweight, and Obese.


Nomenclature
BMI:
Body Mass Index, is an index used to indicate health status based on weight-to-height ratio.
Weight Stigma: The social discrimination against people due to their body weight.
Eating Disorder: A disorder indicated by abnormal eating behaviour such as eating too much or too little.
Obesity: A disease associated with excess body fat leading to serious health concerns.
DEXA: DEXA, short for dual-energy X-ray absorptiometry, is a scan that measures bone density, or the thickness and strength of bones.


2. Methodology

This study critically analyzed recent, reliable research focusing on the impact of BMI within the healthcare industry. The primary data collection tool was Google Scholar, where the keywords "BMI" and "obesity" were used to identify credible sources published in 2024. Additional reputable databases and organizations, including PubMed, the U.S. Centers for Disease Control and Prevention (CDC), the National Institutes of Health (NIH), the Heart Organization, the Multidisciplinary Digital Publishing Institute (MDPI), the Lancet Diabetes and Endocrinology Commission, the American Medical Association (AMA), and the World Health Organization (WHO), were consulted. Each contributed one key study to enrich the dataset and ensure the inclusion of diverse perspectives. The selected studies were critically and objectively analyzed to reflect both supportive and critical viewpoints regarding BMI's utility and limitations in healthcare. Sources emphasizing the practical applications of BMI in identifying health risks were balanced against those highlighting its oversimplifications and potential harms, such as promoting weight stigma or neglecting other health determinants. The inclusion of these varied perspectives was essential to provide a comprehensive understanding of the topic.


3. Results

The BMI scale is commonly used to assess a person's health and fitness status based on their weight-to-height ratio. However, any deviation from the ideal BMI range (18.5–25.0 kg/m²) does not provide a definitive diagnosis but indicates a potential risk that requires further testing. Complementary measures such as body fat percentage, waist-hip ratio, waist-to-height ratio, lean body mass, and cardiorespiratory fitness are necessary to obtain a more accurate health assessment. To enhance its utility, BMI should be supplemented with advanced body composition analysis techniques such as skinfold measurements, bioelectrical impedance analysis, DEXA scans, hydrostatic weighing, and cardiorespiratory fitness1, 3​.
The oversimplified nature of BMI limits its credibility, particularly in distinguishing between fat mass and muscle mass. For example, a healthy muscular athlete may be misclassified as obese, as BMI does not differentiate between muscle and fat. This limitation also renders BMI ineffective for tracking progress during fitness programs, as changes in muscle and fat are not reflected accurately. Similarly, individuals with a BMI below the ideal range may not necessarily be underweight or unhealthy, further questioning its reliability as a standalone metric 1-3,6-8​.
Additionally, the ideal BMI ranges vary across populations, regions, and timeframes. This lack of universality limits the scale's precision and applicability when used outside its intended population 1,3,5​.


4. Discussion

The study findings highlight that, despite being heavily criticized in modern medical research, BMI itself does not directly harm individuals as a health and fitness indicator. Even critics acknowledge the utility of BMI due to its swift and simple approach. However, it is precisely this simplicity that introduces limitations, making it unsuitable as the primary health screening tool. These limitations can be compensated by coupling BMI with other body composition analysis techniques and taking more variables into account1,3​. Relying solely on BMI can lead to misdiagnosis, such as labeling muscular individuals as obese or underestimating health risks for those with a normal BMI but poor health metrics. Such oversights often result in drastic lifestyle interventions that may harm physical and mental health. Weight stigma perpetuated by BMI-centric healthcare practices promotes weight obsession, eating disorders, and severe mental health issues 1-3,6-8​.

These challenges underscore the need to couple BMI with additional body composition analysis techniques and consider other variables, such as genetics, lifestyle, and regional factors. Flexibility in applying BMI within the global healthcare industry is crucial to enhancing its accuracy and relevance. While BMI holds immense potential as a general health guideline, its oversimplifications and unreliable outcomes highlight the necessity for contextualized use.

If no population-specific studies are conducted within a region, BMI outcomes may lack precision and fail to reflect accurate health risks. Nevertheless, minor weight fluctuations are unlikely to render BMI invalid 1,3,5​. The BMI scale retains value as a general weight-guiding tool when used as part of a broader health evaluation rather than a standalone marker.


5. Conclusion

BMI serves as a simple and accessible tool for indicating potential health risks but falls short as a definitive diagnostic measure. Its limitations necessitate further testing using advanced techniques to accurately evaluate an individual's health and fitness. Over-reliance on BMI not only undermines its credibility but also perpetuates harmful practices within the healthcare industry, including stigmatization and inappropriate interventions. While BMI retains its value as a general guideline, healthcare practitioners must exercise caution and contextualize its use within a broader framework of individualized assessments. By doing so, the healthcare industry can preserve the utility of BMI while mitigating its potential harms.


6. Implications and Future Research


1. Research and Development: To improve the reliability and applicability of BMI, further research should explore its integration with advanced body composition analysis techniques. Additionally, studies should examine how BMI varies across populations, regions, and cultural contexts, ensuring its effectiveness as a global health assessment tool.

2. Educational and Policy Initiatives: The widespread reliance on BMI has contributed to weight-centric healthcare practices. Educational programs should encourage healthcare providers to adopt a more holistic view of health, emphasizing factors beyond weight and height. Policy reforms should promote the use of complementary measures alongside BMI to provide comprehensive health evaluations.

3. Prevention and Control: Efforts must be made to reduce weight stigma and prevent the associated mental health challenges. Healthcare systems should prioritize individualized assessments, considering unique characteristics, environments, and lifestyles. By shifting focus from weight-centric metrics to holistic evaluations, the healthcare industry can foster healthier mindsets and practices.


7. References

1. Wu Y, Li D, Vermund SH. Advantages and Limitations of the BMI to Assess Adult Obesity. International Journal of Environmental Research and Public Health. 2024;21(6):757. https://doi.org/10.3390/ijerph21060757.
2. American Heart Association. BMI - Body Mass Index in Adults. American Heart Association. 2024. https://www.heart.org/en/healthy-living/healthy-eating/losing-weight/bmi-in-adults.
3. Sweatt K, Garvey WT, Martins C. Strengths and Limitations of BMI in the Diagnosis of Obesity: What is the Path Forward? Curr Obes Rep. 2024;13(3):584-595. https://doi.org/10.1007/s13679-024-00580-1.
4. World Health Organization. Obesity and overweight. 2024. https://www.who.int/news-room/fact-sheets/detail/obesity-and-overweight.
5. The National Institutes of Health (NIH). Obesity. National Institute of Environmental Health Sciences. 2024. https://www.niehs.nih.gov/health/topics/conditions/obesity.
6. Stefan N, Schiborn C, Machann J, Birkenfeld AL, Schulze MB. Impact of higher BMI on cardiometabolic risk: does height matter? The Lancet Diabetes & Endocrinology. 2024;12(8):514-515. https://doi.org/10.1016/S2213-8587(24)00164-5.
7. Berg S. What doctors wish patients knew about child obesity. American Medical Association. 2024. https://www.ama-assn.org/delivering...octors-wish-patients-knew-about-child-obesity.
8. Zhao L, Park S, Ward ZJ, Cradock AL, Gortmaker SL, Blanck HM. State-Specific Prevalence of Severe Obesity Among Adults in the US Using Bias Correction of Self-Reported Body Mass Index. Prev Chronic Dis. 2023;20:230005. http://dx.doi.org/10.5888/pcd20.230005.​

ARTICLE INFO
Article history:Keywords:
Received 31 OCTOBER 2024
Accepted 14 NOVEMBER 2024
Published 30 DECEMBER 2024
BMI
Weight-Centric healthcare
Obesity
Weight stigma
Eating disorder
Fitness

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About author
Rubab Malik
As a Master of Science in Project Management, with studies in medicine and human resource management, I bring a unique blend of expertise to my writing. With nearly a decade of experience, I've crafted content for a wide range of subjects. Beyond my professional work, I've volunteered as a certified mental health listener, which has deepened my passion for ethical storytelling. Literature and research fuel my curiosity, and I'm excited to contribute to thought-provoking discussions alongside brilliant minds in the academic field.

Latest reviews

This article highlights the benefits and drawbacks of BMI and correctly addressed that it has already been incorporated into various aspects of healthcare and management despite its over-simplification

For a full-fledged report of this study, the methodology, and results would have benefitted from a more in-depth reporting of the sources found and used for this synthesis. Nonetheless, the results appropriately highlighted the various additional metrics complementary to BMI to contextualise the individuals' health.

In the discussion, the author explored the current role of BMI and its questionable suitability as a screening tool. While this is both relevant and important, the use of BMI as a sole means of diagnosis is very uncommon and is typically used as a way to stratify individuals. With that said, the use of BMI does aid the diagnostic and management process, in that it can be used to support diagnoses and be used as additional information during risk stratification.

As re-iterated throughout the article, BMI is not perfect, its simplicity is inherently its weakness. The lack of consideration for genetics, other body parts' composition, and tissue type, etc, should always be considered during clinical care. Inappropriate referencing of an individuals' BMI would indeed contribute towards stigmatization. As highlighted, users of BMI should rely on evidence-based medicine to ensure that 'normal' and 'abnormal' ranges are differentiated to the best of our knowledge, using population-specific studies.

Another argument brought up here is that BMI out of 'normal' ranges leads to potentially-avoidable stigmatization, however, this is not necessarily the case. It may be arguable that discriminatory attitudes and unsolicited lifestyle advices are often faced by those with out-of-range BMIs, however, it is also difficult to separate the effects of in-person/physical encounters. E.g. it may be less likely for a body builder with BMI of 30 to be offered these opinions/comments as opposed to someone with a sedentary lifestyle. In short, the effects of stigmatization is likely multi-factorial too.

Overall, this article brings an important topic into the limelight and discusses the pitfalls of our general over-reliance on BMI. However, additional consideration can be given to the practical difficulties of moving from the simplicity offered by BMI and towards a multi-metric view of weight and body mass.
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