Clinical and field methods to estimate body fat content
Author:
Dr. Daniel Oscar Belluscio 1992-2008.
©All rights reserved
Contents:
1) Looking back, looking forward.
2) Obesity.
........a) Obesity to body
weight.
........b)
Obesity by fat content.
3) Alternative techniques
........a)
Skinfold thickness
........b)
Circumferences
........c)
Bioelectrical Impedance
........d)
Obesity by clinical complications
........e)
Obesity by body fat distribution
........f)
Obesity by adipose cells morphology
........g)
Conclusions
1)
Looking back, looking forward
"Obesity problems are perhaps not so dramatic as the problems
of cancer or polio, but often cause life-long suffering. How many promising
careers have been ruined by excessive fat; how many lives have been
shortened. If some way - however cumbersome - can be found to cope effectively
with this universal problem of modern civilized man, our world will
be a happier place for countless fellow men an women" (ATW
Simeons 1966).
TOP
2)
Obesity
The term Obesity derives from the Greek expression: ob-edere,
which means overeating.
For centuries, it was considered a matter of gluttony, or craving for food, and women were preferred chubby, because chubbiness was erroneously linked to a proper motherhood.
No longer. Many obese patients are rejected by a society that tends to believe that the reason they are obese is because they are unable to control what they eat.
Obesity, like fever and anemia, is a symptom rather than single disease entity: a variety of causes for obesity have been identified in humans and laboratory animals, but in the overwhelming majority of patients the etiology of obesity cannot be determined. Since the underlying causes are poorly understood, it follows that no effective treatment has been developed so far.
This is unfortunate, because obesity is a very common disorder, shortening the life-span of millions of people around the world (421).
During the past fifty years, several treatments have been presented as the solution to this problem. Some could be classified as naïve, others almost useful, and several as health hazardous. Nevertheless, anxious to find relief, patients flock to Medical Centers, Clinics or any other entity that offers a cure to their long-lasting health problem.
Unlike a fever, where a rise in temperature to above 100.4º or 102.2º F indicates the possibility of an underlying clinical disease, obesity is more difficult to characterize. Several methods for assessing the disorder have been recently published.
According to classical Height-Weight Tables, obesity can be broadly described as excess weight as per the usual Life Insurance Tables.
This method is not a good determination of body fat because it only estimates weight. Take two same weight individuals: the one who tends to gain weight around the abdomen may be at a greater risk for heart disease and diabetes mellitus than another whose fat accumulates in the femoral region.
Therefore,
what method can we use to determine what makes an individual obese and
another normal-weight?
TOP
Definitions:
Obesity can be assessed from different perspectives:
........a) According to body weight.
........b) Obesity by fat content.
a.
According to body weight
The definition of obesity as an increase in body weight has prevailed
for many years as the most common clinical tool. It is still being used,
although it is not an accurate measure of obesity (230).
Recently, relative weight has become the most popular and convenient obesity indicator. Relative weight is calculated by dividing an actual weight by ideal weight according to and individual's height, age and sex. A relative weight of 1.20 or greater (i.e.,20% above ideal weight) defines obesity (National Institutes Consensus Development Panel on the Health implication of Obesity, 1985) (230).
However,
there are some problems with real or relative weight. For example, a
person may be overweight without being obese,
and, the degree of overweight at which an individual develops a greater
risk for cardiovascular complications remains subject of debate.
Besides, ideal weight indicators for specific populations have changed recently. We need to be aware of these limitations.
Years ago, the Metropolitan Life Insurance Company issued their Height-Weight Tables. According to these tables, the risk of mortality begins to substantially increase at weights 20 per cent above desirable. A desirable weight was considered a standard weight for any given age and height. Several oversimplified versions of these Height-Weight Tables have become popular throughout these years (318-319).
In these tables, the standard weight for a given age and height is based on the weight that is associated with the lowest rate of mortality for a given height. These tables have some limitations, however. For example, since a table of standard weight is required to determine relative weight, there is no single standard for all patients.
Another problem of these tables is that it is not known how closely an obese patient must approach the standard to satisfactory reduce health risks.
(Click over the image to enlarge and open in a new window)
Currently, the Body Mass Index (BMI) method is experiencing its heyday: this is calculated dividing weight by some power of height (W/Hp). The power function p is selected for a population to arrive at the maximum correlation with body fat and the minimum correlation with body height (263-295).
When p is two, the result is the body mass or Quetelet Index (Kg per m2), the most commonly used weight-height index.(177)
Body mass Index (BMI) closely relates to body fat, while being independent of height (40-263).
Despite some controversy regarding an index of 2 for the power function, a standard value of 2 is more practical, and studies suggested that a value of 2 for p was adequate for men, whereas a value of 1,5 for p was preferable for women.
Since these calculations need to be made every time that weight is estimated, nomograms have been published for this purpose.
However, as in any mathematical calculation relative to an indirect evaluation of body fat, BMI suffers from some inaccuracy (321).
All
these methods - almost accurate as they may be - should be viewed with
caution: normal-weight individuals may show all the clinical complications
of obesity despite being of normal or less than normal weight according
to the weight reported by the scale.
TOP
b)
Obesity by fat content
This may be described as an excess of fat.
Body
weight tank
Accurate
procedures to estimate fat belong to the realm of the Research Laboratories.
For example, determination of cytoplasmic mass from the naturally occurring
isotopes, such as 40 K (316), measurements
of the in vivo dilution of isotopes, like tritiated or deuterated water
(172-305); underwater weighing to determine
body density (302-305); measurements of total
body electrical conductivity with electromagnetic techniques, computed
tomography scanning (170), nuclear magnetic
resonance, neutron activation analysis, dual photon absorptiomethry
(84- 304- 315-501-504), and ultrasonography
(115).
All
these methods can estimate body fat with variable degrees of accuracy,
directly related to performance complexity (134).
TOP
3)
Alternative techniques
Simpler, although less accurate than the preceding techniques, are determinations
of subcutaneous fat by:
........a)
Skinfold thickness
........b)
Circumferences
........c)
Bioelectrical Impedance
........d)
Obesity by clinical complications
........e)
Obesity by body fat distribution
........f)
Obesity by adipose cells morphology
........g)
Conclusions
Determination
of Body fat by means of calipers dates from early 50 S.
Calipers are inexpensive and portable. Measurements are easy to perform,
and are quite acceptable to patients (37-38-128-141-142-191-234-327-328-329-373-435-489)
The technique does not a require a very trained Personnel, and can be
performed on a daily basis, "pinching" the subcutaneous fat
layer located beneath the skin by means of a special caliper.
Several studies were reported assessing the relationship between body
fat and skinfolds. For example, data from the Honolulu Heart Program
concluded that the risk of developing coronary disease is greater for
those with a higher subscapular skinfold thickness at any level of BMI
Body Mass Index.) (134).
Some studies report an acceptable correlation between skinfold thickness
and body fat. These reports concluded that it is possible to estimate
body fatness from the use of skinfold calipers (191).
There are, however, several problems that should be considered when
using skinfold. One of them is the fact that interobserver variations
are considerable. On the other hand, a report from Bray and coworkers
has found greater interobserver differences among skinfold measurements
taken on obese subjects than on lean subjects (191)
The other problem is that not always body fat maintains a good correlation
with skinfolds.
Despite all its limitations, skinfold may yield valuable data concerning
trends in fatness over time within individuals.
TOP
Circumference
measurement is a method that can be compared to Skinfold and Densitometry,
as far as acceptability by patients, ease, and accuracy is concerned
(38-39-72).
It seems that the method is less subjected to interobserver errors than
skinfold thickness, even in obese patients.
The most valuable use of circumference measurements might be in the
field of estimating of body fat distribution (195)
It is therefore possible to characterize obese patients based on the ratio of circumferences of the abdomen (or waist) to the gluteal region. the so-called Waist-to-Hip Ratio (WHR) Any cipher close to 1 forewarns a greater risk for death, stroke and ischemic heart disease. Conversely, a ratio below to, or close to 0.8 decreases the risks for such diseases (152-266-268-518-520)
Therefore
individuals with abdominal obesity are at a greater risk than those
displaying gluteofemoral obesity.
TOP
c) Bioelectrical Impedance (BIA)
Bioelectrical impedance works on the principle that resistance is inversely proportional to total body water, when an electrical current (75 MHz) is applied through several electrodes placed on body extremities.
Impedance has been shown to correlate very well with total body water assessed by more sophisticated methods (190-192-282-305-344).
The
device to estimate body fat by Densitometry is light-weighted, and can
be performed on a daily basis. They are portable, the technique is easily
reproducible and easy to use. The method is quite acceptable to patients
(4).
Electrodes are placed distal to right extremities (Arm and lower limbs)
and homolateral (right half of the body (129-131).
When regression equations are used including weight, height, age, and
sex, correlation of Densitometry with lean body mass as determined by
underwater weighing are near 0.96 It can, therefore, be used outside
the Laboratory settings to assess with great accuracy body composition
(116-283-452-506).
TOP
d)
Obesity by clinical complications.
Obesity could also be defined as a sort of interrelationship between
body weight and complications arisen from body weight. This procedure
seems more coherent as far as the urgency for a medical treatment has
to be considered.
Thus, an individual showing a BMI of 23%, but hypertense should be treated more imperatively than a 30% BMI with no clinical complications in his History. Individuals displaying the android type of body fat distribution could be included in this category.
Several studies suggest a strong association between Body fat distribution, body weight, and high blood pressure, the same correlation observed in hypertensive subjects showing and abdominal type of body fat distribution.
It
has been observed that even near-normal weight individuals may exhibit
these complications despite being slightly overweight.
TOP
e)
Obesity by body fat distribution.
It was probably Morgagni who described for the first time the android
type of obesity in a woman, who had "virile aspectu et valde obesa.".
Later Marañon in Spain and Pende in Italy described respectively
hyperstenic and hypostenic obesities (90)
But was Jean Vague who unquestionably suggested for the first time that body fat distribution and clinical complications, obesity can be split in two categories: Android and Gynoid or the so-called "Pear and Apple-shaped obesities," depending on the anatomical site where fat is more preponderant (123-124-125-257-426-472-473-474-475-476-477-478-480-481-482).
In the android type of obesity, fat is mainly located in the truncal area (upper body, nape of the neck, shoulder, supraumbilical abdomen) When it appears in the female population, they show signs of virilization (hirsutism, more developed musculature) (124-125-167-277-502)
Gynoid obesity, by contrary, displays a female aspect in the subjects (rounded hips, more fat located in the upper part of the body, buttocks, thighs, subumbilical abdomen). Muscular mass is less developed. Women displaying the android type of obesity are subjected to similar complications than males with android overweight
Diabetic and arterial risks for the cases of android obesity are multiplied by a factor or 6 or 20 when compared to gynoid obesity (250-285-306-309-336-346-359-371-416-417-486)
These study matches very well with those showing that blood pressure, gout, several types of cancer were closely associated to a central distribution of fat.
Compared
to males, female populations showing the "gynoid" type of
obesity exhibit more body fat as estimated by Densitometry, but are
in turn less prone to metabolic complications (503).
TOP
f)
Obesity by adipose cells morphology
Excess fat can be stored in an increased number of adipocytes, or in
enlarged fat cells. These two different conditions have been formerly
described as hyperplastic and hypertrophic obesity respectively (49-50-51-52-53-54-84-198-218-223-335-403-404-432)
It was found that enlarged fat cells were highly associated to elevated plasma insulin levels, type I diabetes mellitus, endogenous hypertriglyceridemia and essential hypertension. (49-50-51-279-280).
Hypertrophic obesity was therefore related to metabolic aberrations, whereas hyperplastic obesity was found in early-onset obesity with enlarged visceral organ. It shows a good correlation between fat cell number and total body cell mass (48-81).
Subcutaneous fat layer of young women in the gluteal and femoral regions is mainly due to an increase in cell number (hyperplastic), whereas the abdominal type of obesity correspond to the Hypertrophic type (49-50-51-52)
In women displaying the gynoid type of obesity, fat cell size is smaller in the abdominal region when compared to the femoral area, whereas there is no such difference in men throughout the life span. The female pattern of body fat distribution is maintained with increasing obesity and age
These
different fat depots are subjected to different metabolic regulations,
where sex hormones play an important role in body fat distribution.
TOP
g)
Conclusions
A considerable body of References estimates that normal body fat percentages
are 15-20 per cent in men and 20 to 25 per cent in women. Any cipher
exceeding these standards is considered obesity. Therefore, and based
on Body fat, we could define Obesity as a body fat content of above
30 per cent for women and 25 per cent for men.
Circumference is apt to determine the WHR (Waist to Hip Ratio). A cipher close to (or above) 1 is closely related to clinical complications. Densitometry is a valuable and accurate diagnostic tool, apt to be used in the daily practice.
Regardless the method selected to classify Obesity, all of them concur to a point: Excessive body fat (whether the subject is obese or not according to Height/Weight Tables) is the common denominator to all of them.
We could therefore define Obesity as an accumulation of excessive body fat, well over the daily metabolic requirements of facultative energy storage in the form of triglycerides.
Together
with environmental factors heredity plays a determinant role in the
genesis of this surplus accumulation of body fat.
TOP