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Body mass index measurements don’t take into account the variations to body type by race or ethnicity. A new tool might fix that problem.
Children from different racial or ethnic groups have different body types. With many different body types, why do we continue measuring children with the same assessments?
A new report in the American Journal of Clinical Nutrition investigated whether a novel assessment could be created to measure body fat while taking into account racial and ethnic body type variations.1
Fat-free mass index (FFMI) and fat mass index (FMI) are 2 alternative ways to evaluate nutritional status. These measurements are believed to be a more accurate assessment of nutritional status than body mass index (BMI) or fat percentage, but they still do not take into account differences in children’s body composition based on their race and ethnicity.
Previous studies have shown significant differences in children’s bodies based on race and ethnicity. A study in 2012 study2 published in Obesity found that black children had less body fatness than white children, and that Asian girls had a little bit more body fat than white girls. These differences were noted in BMI-for-age, and there were other calculations to consider. According to the study, excess body fatness varied by race and ethnicity, too, with 89% of black girls being overweight compared to 50% of Asian girls. Additionally, the proportion of overweight girls with excess body fatness were 100% in white girls compared to 62% in Asian girls, the 2012 report revealed.
The new study sought to create reference points for FFMI and FMI in children based on age, race, and ethnic group.
The study team measured body composition, weight, and height in more than 1100 children aged 2 to 21 years without no significant health problems. Fat-free mass was calculated in the study group using measurements of: bone mineral content by dual-energy X-ray absorptiometry, total body water by deuterium dilution, and total body potassium by whole-body γ counting. Fat mass was calculated using the Reference Child and Adolescent models. These calculations were used to compute FFMI and FMI, and these figures were translated into age-based growth curves for black, white, and Hispanic children for each gender.
The FFMI and FMI models were based in the end on 1079 children aged 2 to 21 years. FFMI values for black children were higher than those of white or Hispanic children. The study notes that white and Hispanic children were combined to calculate FFMI models for each gender. For boys, Hispanic children were modeled individually in terms of FMI, but white and black boys were combined. For girls, the FMI was modeled separately for each ethnicity.
The research team concluded that using FFMI and FMI calculations could increase the accuracy of nutrition assessments in children. Finding a reference point has been the challenge, but the research team suggests their new reference points could be the start of a new way to do assessments.
1. Shypailo R, Wong W. Fat and fat-free mass index references in children and young adults: assessments along racial and ethnic lines. Am J Clin Nutr. 2020;112(3):566-575. doi:10.1093/ajcn/nqaa128
2. Freedman D, Wang J, Thornton J, et al. Racial/ethnic differences in body fatness among children and adolescents. Obesity. 2008;16(5):1105-1111. doi:10.1038/oby.2008.30