Body Mass Index (BMI) was invented by a mathematician in the 1830s and later promoted in the 1970s as a screening tool to classify conditions related to extra weight, such as overweight and obesity, at both individual and population levels.
The Importance of BMI in Research
As a categorical value, BMI is undeniably important for research. It helps us understand the impact of weight on health outcomes. For example, observational studies have shown that people with obesity who are physically fit have similar health outcomes to those with a “normal” BMI, while underweight individuals who are unfit have the worst outcomes.
BMI as a Communication Tool
BMI is also a useful communication tool between health professionals. For instance, in an inpatient eating disorder unit, if a GP contacts me with concerns about a patient, using BMI (along with other variables) can help quantify the patient’s risk and determine the urgency of admission. Another example is communicating a high BMI to an anaesthetist before surgery to prepare for a potentially difficult airway.
Limitations of BMI
However, BMI should not be used alone to assess someone’s overall health. It is an arbitrary measure; for example, a BMI of 24.9 is classified as healthy weight, but 25.1 is considered overweight. BMI does not account for factors such as physical activity, diet, smoking/drinking habits, blood pressure, blood glucose levels, mental health, fat distribution (visceral vs. subcutaneous fat), or lean body mass. These factors are equally, if not more, important to health outcomes than weight alone.
The Impact of Weight on Health
Carrying extra weight does increase the risk of some health conditions, and denying this concept is irresponsible. However, it is also stigmatizing and irresponsible for doctors to overemphasize the impact of weight alone compared to other health variables. For example, obesity increases the risk of infertility, and statistically, weight loss can improve the likelihood of conception. However, losing weight does not guarantee pregnancy, and blaming infertility solely on weight is unfair and inaccurate.
Conclusion BMI has a role in research and medical communication, but it should not be the sole focus in individual health counselling. Weight is just one small piece of the much more complex puzzle that is health. 🍎