HOW IS A PONDERAL OVERLOAD AND BODY FAT DISTRIBUTION DETERMINED?
Indirect Methods: Anthropometric Measurements
These include those used, in an indirect form, to address and establish the total fat mass and to classify each individual depending on their weight (body index, ponderal index or through folds, among others) and those used to address the distribution of fat mass in different areas (using the waist/hip index and circumference of the waist).
Body Mass Index (BMI)
This is the most common measurement used and most frequently employed according to the following formula, with weight calculated in kilograms and height in meters:
The principle drawbacks are:
1) It does not distinguish if the ponderal overload is due to fat mass or muscle mass (non-fatty mass) and some muscular individuals can be classified as obese without being so. However, for the general population, variations in weight in individuals of the same size are principally due to fat mass.
2) It does not provide information about the distribution of fat in distinct areas of the body and, as will be explained, it is the visceral or central fat that is related to the majority of incidence of associated illness and mortality.
3)It has a good correlation of body fat in “medium" individuals of 1.6-1.8 meters in height. However, when we consider each individual, it can give a misevaluation of body fat in shorter people and an overestimate for taller people. In other words, the level at which the height of the individual increases, the same percentage of fat mass should be used in the values of the BMI. It also shows too much variability in children and adolescents.
4) Even though there are drawbacks, the BMI formula has been established by different committees and established societies specialized in obesity as the basic measurement used in the initial evaluation of being overweight or obesity in adults.
Ponderal Index
This is one of the most well-known adiposity indexes along with the body mass index and the Roher index, also known under other names. The calculation is done through the following mathematical formula, with the weight determined in kilograms and the height in meters:
The BMI is used to evaluate homogeneous populations in which the majority of the individuals fall under a thin margin when classified by height. The deviation of extreme sizes, without many representatives from large populations, barely influences a global result. However, applying the result to individual subjects, deviations in height that can occur can create results that do not make sense. The results obtained from the BFI formula correspond in a complete way with the percentage of mass body fat and are not affected by height, as occurs with the BMI, making this a more suitable individual study, especially for adolescents and children.
However, the BFI formula, up to this point, has not garnered the relevance or importance as the BMI. In daily clinical practice it is not used very often.
Measuring the coetaneous fold
The measuring of the diverse coetaneous folds has been used to determine the grade of adiposity in subjects. Its usefulness derives from the fact that subcutaneous fat makes up about 50% of total body fat. Measurements using cutaneous folds reflect heavily on the total adiposity of the individual. It can be done in only one measurement or by measuring various areas, which can reduce the chance of error and correct the possible differences in the distribution of fat within the same individual (central or peripheral).
To do this type of measurement a lipocalibrator or calliper is used and the results are obtained in millimetres. The points normally used are the triptic fold (in the middle point between the olecranon and the acromion), the bicipital fold (on the interior face of the arm at the same height of the measurement of the triptic fold) of the non-dominant arm, the subscapular fold (one centimetre below the inferior angle of the scapula, with the arms of the patient relaxed) and the suprailiac fold (two centimetres above the left iliac crest, on the middle line). In each zone three measurements are done and the medium is calculated, giving the final result of the each fold.
There are various equations that, utilizing the measurements of the subcutaneous folds of the patient, are capable of obtaining a precise prediction of the percentage of total body fat. The value of one or several of the measurements of the folds can be used to compare with reference tables according to the sex and age of the individual. It is considered a case of obesity when the measurement is over the 85 percentile on the reference tables.
Indicative parameters of the distribution of body fat
In recent years the importance of the estimation of the distribution of body fat in the different areas of the body (subcutaneous tissue, visceral fat or intra-abdominal) has been recognized as significant and the most trusted method to establish the risks related to the presence of obesity. It is the visceral fat (or intra-abdominal) that, metabolically, is the most dangerous to health, and more so when the index of visceral fat distribution/subcutaneous fat is grater than 0.4
After the decade of the 80s, diverse indicators of visceral obesity came about, like the waist-to-hip ratio (WHR), the waist circumference (WC), the body form index (BFI) and the waist to height ratio (WHtR).
Waist-to-Hip Ratio: This is the most attractive anthropometric parameter for the evaluation of abdominal obesity. Its results have a very good correlation with the quantity of visceral fat, it is very easy to obtain and it can be reproduced over time. The formula is very simple:
To obtain the result a measuring tape adjusted to millimetres is needed; the patient must be standing with their arms relaxed on both sides of their body. The perimeter of the waist is the minimum circumference between the costal border and the iliac crest; the perimeter of the hips is the maximum circumference between the waist and the thighs.
It has been established that there is a risk factor for the development of illness associated with obesity when the WHR results are greater than 0.9 in females and greater than 1.0 in males.
Waist Circumference: More and more there is evidence that demonstrates that the isolated determination of the perimeter of the waist (WC) has similar value as the WHR. This measurement is simpler and correlates well with the indexes mentioned above and total body fat. The reference values vary depending on race and population. In the European race it is considered a risk factor when the WC is more than 82 cm in females and more than 95 cm in males (being that the risk is highly elevated in females and males when it is greater than 90 cm and 102 cm, respectively).
Others: Some authors have recommended an adjustment to the WC with size and the use of the WhtR; it has not been confirmed which has a better correlation to visceral fat or which is a better predictor of illness or mortality, the WHR or the WC. The BFI has been used as the predictor of central obesity, but with little success.