Body fat is superior to the flawed BMI. BMI is an imperfect measurement, and yet it is still useful, at least in a general way. The BMI formula developed in the 19th century by a Belgian statistician and sociologist. Overweight and obesity is an increasingly important health variable which has been shown independently to influence mortality and morbidity in adults and children. The use of BMI as a measure of weight status is widespread. This understandable due to its simplicity, cost and labor effectiveness compared with other body fat assessments.
The validity of BMI is based on the assumption that as BMI increases so does adiposity (fat tissue). However, researchers have begun to question this assumption. Studies are finding that BMI and Body Fat do not follow the same linear track. For example, a thin woman who gains 2.2 lbs. could represent an increase of 2.3% body fat, but for an obese woman only a 0.3% increase in body fat.
This difference is absolute body fat percentage versus BMI would underestimate the thinner woman and overestimate the heavier woman. BMI misrepresents measurements for child and adults, rendering assumptions made about a child’s BMI an invalid projection about that child’s adult BMI status.
Calculating body fat percentage:
- Total fat in lbs. / total bodyweight X 100.
- Body fat is a known risk factor for obesity, metabolic disorders, cardiovascular disorders, depression, stroke and sudden death.
- In kilograms and meters, weight (kg) / [height (m)]2
- In pounds and inches, weight (lb) / [height (in)]2
There have been several improvements over the years defining what is meant by being overweight and helping us understand the fight against the obesity epidemic. In an effort to guide future generations toward physical activity, optimal body fat and health, it is important to grasp how measurements of weight, fat and BMI differ between children and adults. It is important that we stay informed as to improvements in measurement techniques for both children and adults. Being informed will allow everyone to make more informed assessments.
Ideal Body Fat Percentages
Each of us is genetically programmed to be a certain body type, so it is natural for some people to carry more fat than others. A healthy body needs fat for normal physiological functioning. There are two types of body fat; essential fat is required for the hormonal and immune systems to function and storage fat is used for fuel. Women tend to carry four times the essential fat as men, as it is biologically important for childbearing and other hormone related functioning.
Body fat is superior to the flawed BMI
As stated earlier, BMI is not a good diagnostic tool for children. A child may have a high BMI for their age and gender, however determining whether excess fat is a problem requires further assessments (with adults as well). For this reason, a healthy weight range is not possible for most pre-teen and adolescents, as their bodies are changing rapidly throughout these years.
New research shows a normal BMI can hide metabolic abnormalities. Individuals who fit into the “normal” range for height and weight can suffer disorders; scientist understands now that our bodies handle nutrition differently. Researchers have begun documenting the different ways metabolic condition like insulin resistance elevates the risk of heart disease and Alzheimer. One in four people with a “normal” BMI experienced some form of metabolic abnormality, according to a 2008 study.
An elevated BMI does not necessarily equate to poor metabolic health. Fifty percent of all people who are overweight experience zero metabolic abnormalities. In fact, people who are overweight but not obese live longer, than people with normal BMI’s. However, this isn’t the same as saying if you’re overweight all is O’k. Everyone’s body is different, there doesn’t appear to be a one size fits all situation.
Gorman, C. (2013). What’s Better Than BMI?. Scientific American, 309(5), 21-22.
Duncan, M., Mota, J., Vale, S., Santos, M., & Ribeiro, J. (n.d). Comparisons between inverted body mass index and body mass index as proxies for body fatness and risk factors for metabolic risk and cardiorespiratory fitness in portuguese adolescents. American Journal Of Human Biology, 24(5), 618-625.
Duncan, M. J., Martins, C., Silva, G., Marques, E., Mota, J., & Aires, L. (2014). Inverted BMI rather than BMI is a better predictor of DEXA determined body fatness in children. European Journal Of Clinical Nutrition, 68(5), 638-640. doi:10.1038/ejcn.2013.285
Nevill, A. M., Stavropoulos-Kalinoglou, A., Metsios, G. S., Koutedakis, Y., Holder, R. L., Kitas, G. D., & Mohammed, M. A. (2011). Inverted BMI rather than BMI is a better proxy for percentage of body fat. Annals Of Human Biology, 38(6), 681-684. doi:10.3109/03014460.2011.606832
Separately Assess Body Weight, Body Fat, and BMI. (2011). Running & FitNews, 29(2), 3-8 6p.