At some point in a person’s life, a discussion with their doctors about Body Mass Index, commonly known as BMI, will occur. BMI is a simple number that represents a person’s weight-to-height ratio. However, today, health practitioners are finding clinical limitations with this measurement. So what are these limitations? And how can clinicians deal with these issues to really understand a person’s complete body composition? This article takes a deep dive into these topics and reveals how one company’s technological advances in body composition analysis are changing the game in disease prevention and treatment.
BMI Limitations
BMI measures body fat, and research shows that excess body fat, especially visceral fat, is linked to an increased risk of health issues, including diabetes, cardiovascular disease, and even osteoporosis. According to the Centers for Disease Control and Prevention (CDC), BMI is a measure of weight adjusted for height, calculated as weight in kilograms divided by the square of height in meters. However, the CDC also reveals that BMI is a surrogate measure of body fatness because it measures excess weight rather than excess body fat. So why is this an issue? BMI can overestimate body fat in athletes or individuals with a large amount of muscle mass. It can also underestimate body fat in older adults or people with very little muscle mass. So with the limitations of BMI, what other measurements are health practitioners using when assessing body composition?
Some clinicians measure abdominal fat using tools such as waist-to-hip ratio, skinfold thickness, or waist circumference. However, these measurements also come with limitations ranging from loss of information to lack of standardization. BIA (Bioelectrical Impedance Analysis) is another measurement tool that can estimate body composition by running a small electrical current through the body. Conventional BIA devices use empirical estimations based on factors like age and sex to help improve accuracy. While this may work for people with a standard body type, it is inaccurate for those who do not fit this mold. So with all these limitations – what needs to change so that clinicians can get a true picture of their patient’s health? It starts with building more comprehensive and accurate tools of measurement.
To better understand the limitations of BMI and BIA and why addressing these issues is critical to disease prevention and patient care, Endominance spoke with Mary Weyrick, Assistant Director of Clinical Research at InBody. InBody is a leader in body composition technology.
VS: Many medical health professionals feel that traditional BIA/BMI is inaccurate and misleading. Do you agree and why?
Weyrick: “We feel BMI truly misses the mark for sarcopenic obese individuals with low muscle mass and high body fat and who are miscategorized as healthy because of their low body weight. Or, with athletic individuals who typically score above the healthy weight range because they possess a high amount of lean mass and yet are prescribed weight loss treatments and even denied transplant surgery as the implication is there would be too much visceral fat to circumnavigate in harvesting or grafting the organ. This is why I believe studies began to emerge as early as 2004, which found BMI does not provide insight into regional body fat distribution (P. Kok et al., 2004). The same could be said of traditional BIA methods. The principle of BIA is that it sends low-level electrical currents through the body and measures the resistance it experiences as it passes through body water, also known as ‘impedance.’ Impedance characteristics are inversely proportionate to the diameter of the path. This means if the path the current takes is wide, the impedance is low. And if the current is short, the impedance is also low. When we consider the trunk [of the body], which is anatomically short and wide, the impedance is significantly lower, only about 5-10% of the impedance found in the arms. And, since the trunk is also about 50% of our body weight, this means that if the impedance measured was the same in the trunk and arms, it would not mean the same amount of muscle mass was present. Yet, traditional methods consider the entire body a single cylinder, which means impedances and segmental values can be misleading.”
Weyrick also cited other issues with traditional BIA. She states, “Another inaccuracy in earlier BIA is its use of a single low frequency of 50 kHz, which does not penetrate the cell membrane and mainly reflects extracellular water values. We know the human body consists of intracellular and extracellular water, which requires low to high frequencies to capture total body water. Cognizant of this, traditional BIA looked to empirical estimations based on trends in individuals within a specific set of demographics (for example, age, gender, ethnicity, etc.) to obtain a complete body composition. However, this resulted in yet another side effect for individuals who are far from the average of that population.” Weyrick stated additional issues resulting from using empirical estimations based on trends in individuals within a particular set of demographics. Some of the critical problems included:
- Overestimations of body fat percentage in athletic women and underestimations in small-framed men with high body fat levels. If these statistical analyses govern the outputs, the empirical estimation produces errors whenever a subject does not belong to an average group.
- Insensitivity to compositional changes. When doctors treat obese patients, they test body composition analysis repeatedly to monitor the effectiveness of treatment. In this case, a machine using population-specific empirical estimations underestimates the compositional changes of the patients.
- Inadequate research. Consider a study in which there is a comparison of body fat percentage between male and female individuals in their 50s. The results will be programmed data rather than actual differences if an analyzer is pre-programmed to consider the differences of sex and age. Therefore, machines using this empirical estimation are inadequate for differentiating body composition between groups.
VS: How does InBody address these issues? And why is this important?Weyrick:
“Re-introducing BIA for best practice in clinic and research has been InBody’s focus since the ’90s. We experienced skepticism earlier on because of the reasons already mentioned. In essence, they apply equations on individuals outside of the specific demographic population they were designed from. Additionally, people within a specific group of demographics also have significant variances in factors such as diet, exercise, medications, and medical history that empirical trends are simply unable to capture. This variation can be seen in the ‘healthy’ with even greater variances seen in medical populations or in the same way no two cancer patients experience the exact same symptoms. What InBody did was develop a technology called Direct Segmental Measurement (DSM-BIA). It assumes the body is comprised of five distinct and unique cylinders of four limbs and one trunk and measures the impedances of these parts separately. Separate measures ensure the data from each body is accurate and not skewed or influenced by each other. This technology also uses low to high frequencies, 1kHz to 3MHz, which allows you to obtain total body water and differentiate between intracellular and extracellular water. This technology is a vast improvement from traditional methods, which estimate intracellular water from extracellular water. This is important since intra and extracellular water is proportionate to one another in a healthy body. But imbalances in fluid distribution occur in the vast majority of those who are elderly, suffer from obesity, or are critically ill – the very individuals who need to analyze their body composition the most.”
VS: Why do you feel getting a person’s complete and holistic body composition matters?
Weyrick: “A holistic approach to body composition is essential because our cognitive health affects our physical health and vice versa. How we think impacts how we feel, determining our behavior and how we physically interact in our environment. If someone is told their body fat percentage is high, a shift in thinking is needed for sustainable, long-lasting change. Bariatricians are aware of this critical piece which is often why their patients begin healthy habits before weight loss surgery and receive counseling to ensure a mindset change in tandem with their physical transformation. In other words, the very best, effective medical treatments are ones that improve Quality of Life which is defined by the ‘standard of health, comfort, and happiness experienced by an individual or group.'”
InBody also states on their website that their devices can be used as an adjunct tool for clinical decision-making so that clinicians can develop more effective treatment and prevention strategies. For example, one of their body composition analyzers can manage patients’ diabetic risks and symptoms. Diabetes is often associated with excess fat; however, having insufficient muscle mass is just as detrimental and increases diabetes risk. Leg muscles serve as a driver for glucose uptake, and low leg muscle mass is associated with an increased risk of insulin resistance. With InBody, medical professionals can assess and monitor a patient’s muscle and fat composition. By observing these factors and setting specific treatment programs, physicians and educators can track the progress and success of treatments and healthcare interventions.
