C H A P T E R 7 cant to be informed about the start of the discrepancy between height and weight of the Dutch population. Taking into account the information that height does not increase anymore, the increase in Body Mass Index (BMI), which was seen in the postnatal data, means a higher increase in weight. Methods of analyzing growth of children There are several methods to analyze the growth of a child and to determine over-‐ weight or obesity. One can compare particular children of the same age, gender and population to judge if its weight and height are within the normal range for the population. Usually weight and height are expressed as a function of age. Weight can also be expressed in relation to height as the BMI defined as weight (kg) divid-‐ ed by squared height (m2). However, the above-‐mentioned tendency of the popula-‐ tion to become heavier with steady size led to an increase in the BMI as followed from the formula. In case of an equal weight to height ratio a child (below the age of 10 years) with a taller height has a higher BMI in contrast to a child (below the age of 10 years) with a smaller height, taking the P3, P50 and P97 values into account. Therefore the expression of weight versus height is more reliable in children. A limitation of the anthropometric approach of weight is that the BMI as well as weight for height does not distinct between fat mass (FM) and fat-‐free mass (FFM)6. In adipose children it is reasonable to ascribe the weight gain to an increase in FM. At the same time in relatively lean children a lower weight is largely due to a shift from FM to FFM. Because a large part of the FM is situated in the abdominal region, Fredriks stated that waist circumference can be used as a better tool to screen for increased abdominal fat in children7. To measure total body fat one needs the use of other methods. A rather complex method is the underwater weighing. The difference of weight in the open air and under water gives a good indication of the FM. An easy and reliable method is the measurement of the FFM by means of Deuterium. Deuterium is a stable isotope of hydrogen of which the natural presence in the body fluids is knowable by measur-‐ ing Deuterium in the urine. After a known gift of Deuterium the new concentration in the urine after equilibration of the Deuterium in all body segments, is equivalent with the total body FFM. Distracting the result from total body weight delivers a good estimate of total body fat. Minimal changes in body composition can be found by using the Deuterium method. 108
Proefschrift binnenwerk Manon Ernst_DEF.indd
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