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Updated 14 April 2015

Forget BMI, these are better ways to measure your body fat

In the light of the limitations of the BMI, DietDoc discusses a number of other ways to determine how fat – or not – you are.

1


Last week we discussed the use and accuracy of the BMI (Body Mass Index). Some readers may be worried that the BMI’s accuracy of 88% is not sufficient to indicate if they are fat or not, so let’s consider a few other methods.

Waist circumference and waist to hip ratio


This measure of body fatness helps to pinpoint if the patient tends towards android or “apple-shaped” or visceral obesity compared to gynic or “pear-shaped” fat distribution. Android fat distribution is associated with fat deposits in the abdomen.

The many beer-bellies or “boeps” we see in our malls and on our beaches are visible evidence of android obesity. Gynic fat distribution indicates fat stored under the skin in areas such as the “love handles” or the hips and thighs, a deposition that is more common in women.

Read: Banish those love handles!

Both android and gynic fat distribution are not good for health, but apple-shaped individuals with large stomachs are exposed to more risk than pear-shaped people.

Research indicates that people with android obesity are more vulnerable to diseases of lifestyle such as heart disease, diabetes, hypertension, stroke, raised blood fats, arthritis, gout, and metabolic syndrome.

Both the waist: hip ratio (WHR) and the simpler waist circumference measurement can be used to determine body fat and its distribution to assess risk of disease.

a) Waist circumference


The Waist Circumference (WC) is defined as “the shortest circumference measured halfway between the lower rib margin (bottom of the ribs) and the iliac crest (top of the hip bone) as palpated on both sides". The person being measured must be standing in a relaxed position and have exhaled.

This measurement may not be quite as easy to determine as measuring one’s height and weight for the BMI, but if in doubt ask a healthcare professional or a biokineticist to help you. 

Men: WC greater than 40 inches or 102 cm = high risk of chronic diseases of lifestyle no matter if you are obese or not!

Women: WC greater than 35 inches or 88 cm = high risk of chronic diseases of lifestyle no matter if you are obese or not!


b) Waist to hip ratio


In addition to measuring your WC, a second measurement of hip circumference on the level of the pubic bone when you are standing with your feet together can be combined with the WC to calculate your w:h ratio. In very obese patients it may be very difficult to measure the hip circumference.

Men:
If your waist: hip ratio is equal to or lower than 0,8 then risk of diseases of lifestyle is low; if the ratio is equal to or exceeds 1.00, then the risk is very high.

Women:
If your waist: hip ratio is equal to or lower than 0,7 then risk of diseases of lifestyle is low; if the ratio is equal to or exceeds 0.8, then the risk is very high.

The ABSI (a body shape index)


Krakauer and Krakauer have suggested that a combination of the BMI and body shape (as indicated by the WC) particularly of abdominal fat deposits, would more accurately pinpoint who is exposed to the greatest risk of mortality. The new body shape index or ABSI uses the WC but adjusts for height and weight.

Read: Pear-shaped bodies not healthier

In a study conducted with more than 14,000 American adults from the NHANES 1999-2004 study, who were followed up for an additional 5 years to determine mortality (828 deaths), Krakauer and Krakauer found that people with high ABSI values had a higher risk of death and that the ABSI was able to predict death rates in this population. These results were not influenced by age, sex, BMI or white or black ethnicity. 

The authors concluded that, “Body shape, as measured by ABSI, appears to be a substantial risk factor for premature mortality in the general population, derivable from basic clinical measurements. ABSI expresses the excess risk from high WC in a convenient form that is complementary to the BMI and to other known risk factors.”

However Krakauer and Krakauer, do caution that the ABSI must be tested in other ethnic groups such as Mexican Americans.

The Deurenberg Equation


This equation uses the BMI, gender and age of the patient to calculate % body fat as follows:            

% body fat = (1.2 x BMI) + (0.23 x age in years) - (10.8 x G) - 5.4

G = 1 for men; G = 0 for women

Example:

A woman aged 25, with a BMI = 30 and G = 0 (female) would have the following % body fat:

% body fat = (1.2 x 30) + (0.23 x 25) - (10.8 x 0) - 5.4

= 36 + 5.75 - 0 - 5.4

= 36.4%

Women:
% Body Fat exceeding 25% to 32% is excessive and linked to the metabolic risks listed above.

Men:

% Body Fat exceeding 20% to 25% is excessive and linked to the metabolic risks listed above.

Conclusions


In general, measurements like the waist circumference and formulas such as the BMI and the Deurenberg equation can be used with a satisfactory measure of accuracy to predict body fatness and potential risk of disease for the general adult population. As Christine Gorman observed in Scientific American when referring to the BMI, “[It] may be outdated, but it still works”.

These formulas are however, not recommended for use in children, adolescents, pregnant or breastfeeding women, very obese individuals, patients suffering from anorexia or a wasting disease, and sportsmen and women who have a much larger proportion of muscle tissue than of fat tissue.

Read: Fat to blame for half a million cancers a year


The new ABSI (A Body Shape Index) proposed by Krakauer and Krakauer, is showing promise particularly to predict vulnerability to mortality caused by overweight and obesity.

Next week we will have a look at the results of studies to compare the use of bioelectrical impedance measurements (which are so popular with fitness instructors at gyms), with the results of some of the other methods mentioned in these first two articles on measuring body fatness. 


Read more:

How accurate is the BMI?

Rethinking body mass index for assessing cancer risk
BMI can predict heart disease

References:

- Esco MR et al (2011). Cross-validation of BMI-based equations for predicting percent body fat in female collegiate athletes. Journal of Exercise Physiology, 14 (2):43-50; FPD (2001).

- Certificate Course in the Management of Obesity. Foundation for Professional Development, 13-14 Sept 2001, Centurion.
- Gorman C (2013). BMI is outdated, but it still works. Scientific American, 15 October 2013: http://www.scientificamerican.com/article/bmi-is-outdated-but-it-still-works/
- Kaslow JE (2015) Body impedance Measurement.
- Krakauer and Krakauer (2012). A new body shape index predicts mortality hazard independently of body mass index. DOI:10.1371/journal.pone.–39504.
- Mahan K L et al (2012). Krause’s Food & the Nutrition Care Process. Elsevier Publishers, USA.


Image: Measuring body weight from Shutterstock


Dr Ingrid van Heerden is a registered dietician and holds a doctoral degree in Nutrition and Biochemistry. She believes that "we are what we eat" and offers free nutrition and weight loss advice via her DietDoc service on Health24.com. Read more of her articles.

 
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