Abstract
Background: Body mass index (BMI) is currently the universal tool used to measure obesity and “fatness” in health. However, in recent years an emerging body of literature has reported some limitations to BMI as it does not take body composition, age, sex and ethnicity into consideration. Aotearoa/ New Zealand (NZ) is ethnically diverse and has different demographics when compared to other countries in the world. Therefore, it is important to further explore the relationship between body size, body composition and BMI across different ethnic groups in Aotearoa.
Aims: Firstly, to understand the relationship between body size (height and body surface area (BSA)) and body composition in an ethnically diverse and healthy cohort. Secondly, to understand the relationship between body composition and BMI in an ethnically diverse and healthy cohort.
Methods: 258 participants from the NewERA (New Echocardiographic Reference ranges for Aotearoa) cohort were included in this study. Participants self-identified sex (112 male and 146 female) and ethnicity (Māori male N=23, Pacific Island People (PI) male N=29, NZ European male N=60, Māori female N=43, PI female N=28, NZ European female N=75). Differences in demographics (age) and body composition (weight, height, BMI, BSA, fat free mass (FFM), fat mass (FM), muscle mass (MM), body fat percentage, visceral fat rating, and bone mass) were examined between ethnicities and the relationships between variables were investigated using appropriate statistical methods. There was no formal comparisons made between sexes.
Results: At a similar height and BSA, for all body composition variables (weight, FFM, MM and FM), NZ Europeans had the lowest values, followed by Māori and PI had the highest. At a similar BMI, this was also true where NZ Europeans had the lowest body composition values, followed by Māori and then PI. At higher BMI categories it was also shown that Māori and PI were leaner (higher FFM percentage) when compared to NZ Europeans. BMI was most strongly associated with FM whereas BSA was more strongly associate with FFM across all ethnicities in both sexes.
Conclusions: This study has highlighted that BMI is a poor indicator of body composition in the NewERA cohort. Health should not be measured using a simple and inaccurate tool. The measure of an individual’s “fatness” or body fat (BF) should be their BF percentage and not BMI. We need to move away from simple calculations that estimate a person’s body composition and should simply measure them. We need to consider that health has many components, and measurements are only one part, the person, and their physical health, including physical activity, as a whole needs to be considered.