There has been much debate between the benefits of Body Mass Index (BMI) measurement as opposed to body-fat percentage scores. Whilst body mass index bmi takes into account body weight and height, body fat percentage measures the body composition. That is the fat mass, or amount of body fat, in comparison to lean mass (everything else after the fat measurement has been deducted).
One of the problems with body mass index measurements is that it is a very simple measurement. Likewise, one of the problems with the body fat percentage measure is that not only does the percentage of body fat vary according to gender and age but also according to race. This factor would need to be taken into account for any body fat measurement in the future.
Medical study on Age, Gender and Race and body fat percentage.
The 2002 Heritage medical study shown below, in full, examined the relationship between sex, age and race on body mass index and body fat measurements.
Comments and Key Points
This study compared 665 white and black Americans, both men and women aged 17 to 65. Body Mass Index and body fat percentage were analysed. I’ve summarized the findings in a table below, for the benefit of people looking for this type of data.
|BMI||% fat||BMI||% fat|
This study found no defined difference in body fat percentage in men, regardless of race. However, black women are heavier, their ratio of fat to Body Mass Index is similar. Actually, this study found a slight difference between black women and white women, but only when their Body Mass Index (BMI) is less than 25. No big deal.
This graph of Body Fat percentage versus Body Mass Index, shows that women’s fat percentage is higher than men’s. For the same body mass index, the percentage of body fat in females was 10.4% higher than that of males. The curving data trend lines, shown below, look similar to other studies of body mass index versus body fat percentage.
The article referred to 4 different equations that can predict body fat percentage, from Body Mass Index (BMI).
|Deurenberg formula1 #1:||Adult Body Fat % = (1.20 x BMI) + (0.23 x Age) – (10.8 x gender) – 5.4|
|Deurenberg formula2 #2:||Adult Body Fat % = (1.29 x BMI) + (0.20 x Age) – (11.4 x gender) – 8.0|
|Gallagher formula3:||Adult Body Fat % = (1.46 x BMI) + (0.14 x Age) – (11.6 x gender) – 10|
|Jackson-Pollock formula4,5:||Adult Body Fat % = (1.61 x BMI) + (0.13 x Age) – (12.1 x gender) – 13.9|
These formulas are graphed and compared in the chart below:
These formulas graphed are all fairly similar. Trouble is, they are linear formulas (giving straight lines), but the real relationship between Body Mass Index (BMI) and body fat is a curved one, as you saw higher up on this page.
This article also suggested it’s own formula for predicting body fat percentage from BMI, age and gender:
|Heritage study:||Adult Body Fat % = (1.39 x BMI) + (0.16 x Age) – (10.34 x gender) –
One important conclusion of this study, is to notice that AGE is a significant part of all these body fat formulas. This indicates that it is not suitable to use a fixed BMI across all ages as a definition of obesity. Also, these formulas tend to overestimate the amount of fat in young men with a Body Mass Index of over 30.
“results are consistent with published data showing the need to consider age and gender when defining the prevalence of obesity with BMI“.
This article suggests that for body fat, 25% for men, and 33% for women, are suitable cutoff thresholds for defining obesity6. Using these body fat percentage cutoff figures, and using their formula to relate BMI to body fat, and using the mean Ages in the study, this table shows the BMI values that could achieve the body fat percent cut offs.
So, to summarize, in the last table, a BMI of 27.7 for men, and BMI of 26.3 for women, could be suitable BMI thresholds to define obesity (although sensitivity and specificity might need adjusting).
Suppose you were a young adult woman with a BMI of 20. The linear formula would give you a body fat measurement of about 25%. But, look at the curvy chart a little higher up, and you’ll see the body fat value should be about 18% or less.
Questions and Answers.
How do you actually measure body fat?
There are several ways of measuring body fat for a detailed look at these click here. There is skin fold testing using a body fat calculator and bioelectrical impedance analysis using fat scales, such as ‘ozeri touch’ that give you a body fat measurement. You can use a body fat calculator that gives a percentage of body fat based on BMI and body measurements with a tape measure. There are more high-tech methods such as hydrostatic weighing, dexa scan and the bod pod.
I carry a lot of abdominal fat. Would this show up in a body fat percentage?
Most body fat percentage calculator do not take into account where the body fat is located. Having a large waist circumference in relation to your body size does carry some health risks for obesity-related diseases such as high blood pressure and heart disease. There are several ways to lose your belly fat , so calculate your body fat and get started as soon as possible.
What is a healthy body fat percentage?
Different health specialists have different formulas and ranges for what percentage of fat and lean mass composes a healthy body – or how much body fat is not healthy. The American Council on Exercise (ACE) say the upper limit of healthy fat for men is 25% and for women 32%. Dr. Halls prefers a 33% cut off point for women. It is normal to carry extra body fat as you age.
How do I start losing fat and gaining muscle mass?
First you have to calculate your body fat. You will need to look at all areas of health and fitness. Start with a healthy eating plan for life such as the Mediterranean diet. Join a gym, employ a personal trainer and introduce some exercise, especially resistance training into your routine. Use our very own weight loss percentage calculator.
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- Deurenberg P, Westrate JA, Seidell JC. Body mass index as a measure of body fatness: age- and sex-specific prediction formulas. Br J Nutr 1991; 65:105-114.
- Deurenberg P, Yap M, van Staveren WA. Body mass index and percent body fat. A meta analysis among different ethnic groups. Int J Obes Relat Metab Disord 1998; 22:1164-1171.
- Gallagher D, Visser M, Sepulveda D, Pierson RN, Harris T, Heymsfield SB. How useful is body mass index for comparison of body fatness across age, sex and ethnic groups. Am J Epidemiol 1996; 143:228-239.
- Jackson AS, Pollock ML, Ward A, Generalized equations for predicting body density of women. Med Sci Sports Exercise 1980; 12:175-182.
- Jackson AS. Research design and analysis of data procedures for predicting body density. Med Sci Sports Exercise 1984; 16:616-620.
- Wellens, RJ, Roche AF, Khamis HJ et al. Relationships between body mass index and body composition. Obes Res 1996; 4:35-44.