Why BMI is Not a Reliable Health Indicator


Body Mass Index (BMI) has long been hailed as a go-to measurement for assessing health and weight status. Yet, its credibility as a reliable health indicator is questionable. As a dietitian with a focus on mental health and considering an individual holistically, I believe it’s crucial to understand why relying solely on BMI can be misleading and harmful.


Origins of BMI


Firstly, let’s delve into the origins of BMI. Developed in the early 19th century, BMI was formulated based on data from a predominantly white, male, European cohort. This narrow demographic representation should mean that it is inappropriate to apply this measure to diverse populations. (However our health system does it anyway).


The creation of BMI was intertwined with eugenics. Eugenics is a set of beliefs and practices that aim to ‘improve’ the genetic quality of a human population. Historically, eugenicists have attempted to alter human gene pools by excluding people and groups judged to be inferior or promoting those judged to be superior. As you can see from this definition, BMI comes from problematic origins.


Weight ≠ Health


It’s essential to recognise that weight is not synonymous with health. The BMI-centric approach overlooks crucial factors such as body composition, ethnicity, muscle mass, and our natural ‘weight set point’. This oversimplification can lead to misclassification of health risks, with the pathologising labels of ‘overweight’ or ‘obese’ given to those who may be metabolically healthy. While others may fall within the ‘healthy’ range despite their body being low weight. This is common occurance in those with hypothalamic amenorrhoea (loss of menstrual periods). Often, they are told they have a ‘healthy’ BMI perhaps around 19 or 20, but for their bodies this is too low. Women need a certain amount of body fat stores to ensure regular menstruation and for most women a BMI over 20 is required for this.


How BMI can cause harm


BMI-centric health systems can perpetuate discrimination and impede access to care.

For instance, relying on BMI-based criteria for interventions in eating disorders can result in delayed interventions and worse outcomes. Similarly, fertility care often imposes BMI restrictions, disregarding the complex interplay between weight and reproductive health.


Alternatives to BMI


So, what should we focus on instead? As a dietitian, I advocate for a holistic approach to health that considers multiple indicators beyond weight alone. Energy levels, vitality, sleep quality, weight history and family history, mental health, and blood work provide valuable insights into one’s overall well-being. By using a number of different factors to look at an individual as a whole, we can build a more inclusive and empowering approach to health.

In conclusion, BMI fails to capture the complexity of human health and can perpetuate harmful stereotypes and barriers to care. As we strive for a more inclusive and compassionate approach to health, let’s embrace a holistic perspective that values individual experiences and recognises the multifaceted nature of well-being.

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Blog written by Sophie

Sophie is a Specialist Eating Disorder Dietitian passionate about delivering great quality care and advocating for her clients. She is naturally curious and driven for continued learning both within the profession and outside of it. Sophie founded Mental Health Dietitians in 2024 to be able to work in a way that is value-aligned and makes a difference to the individuals in her care. As well as the wider profession. She currently supports international clients 1-1 in her online clinic.