Body fat based weight norms for children and youths

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1 ORIGINAL ARTICLES / Prace oryginalne Pediatric Endocrinology, Diabetology and Metabolism 09, 15,, ISSN 124-6X Romuald Stupnicki 1, Paweł Tomaszewski 1, Katarzyna Milde 1, Jan Czeczelewski 2, Małgorzata Lichota, Joanna Głogowska 1 1 Department of Statistics and Computer Sciences, Chair of Anatomy and Biomechanics, Józef Piłsudski University of Physical Education in Warsaw, Poland Zakład Statystyki i Informatyki, Katedra Anatomii i Biomechaniki Akademii Wychowania Fizycznego Józefa Piłsudskiego w Warszawie 2 Department of Hygiene and Health Promotion, Józef Piłsudski University of Physical Education in Warsaw, Biała Podlaska Branch 2 Zakład Higieny i Promocji Zdrowia Akademii Wychowania Fizycznego Józefa Piłsudskiego w Warszawie, Wydział Zamiejscowy Wychowania Fizycznego, Biała Podlaska Department of Correction, Józef Piłsudski University of Physical Education in Warsaw, Biała Podlaska Branch Zakład Korektywy Akademii Wychowania Fizycznego Józefa Piłsudskiego w Warszawie, Wydział Zamiejscowy Wychowania Fizycznego, Biała Podlaska Address for correspondence: Paweł Tomaszewski, PhD Zakład Statystyki i Informatyki, Katedra Anatomii i Biomechaniki Akademii Wychowania Fizycznego Józefa Piłsudskiego w Warszawie ul. Marymoncka 4, Warszawa; pawel.tomaszewski@awf.edu.pl; katarzyna.milde@awf.edu.pl Abstract Introduction: The issue of establishing reference values, especially of those pertaining to somatic features, is of importance for an assessment of normal growth. It was assumed that norms ought to reflect not the actually existing status but the recommended one. Thus, weight-height relations, including Body Mass Index (BMI), ought to be established for that fraction of the general population, in which body fat content is within physiologically acceptable limits. The aim of the study: To construct weight-to-height percentile norms for boys and girls aged 7- years. Material and methods: A cohort of healthy boys (n=1282) and girls (n=11) attending schools in the Eastern regions of Poland participated in the study. Their body height, body mass and body fat content were determined, the latter by skinfold (Slaughter s method) or bioimpedance measurements. The data for constructing normal values of body fat content were compiled from diverse sources so as to associate them smoothly with the normal values for adults. Results: By applying the proposed lower and upper limits of body fat, 07 boys (78.5%) and 581 girls (.5%) with acceptable fat content were selected for constructing percentile norms of body mass expected for height, as well as for BMI. Conclusions: The existing norms for BMI of children and youths, also the Polish ones, differ from each other, as these were not based on data from subjects with acceptable body fat and assessing body fat content from BMI is known to be markedly biased. Unlike BMI, the presented percentile weightfor-height norms are age-independent in the range 7- years and are thus much easier to use. Those norms may be recommended as a tool in assessing the course of normal growth, as well as in developmental disorders and possible clinical intervention. k e y w o r d s : body fat content, weight-height norms, Body Mass Index, boys, girls Streszczenie Wprowadzenie: Zagadnienie konstrukcji norm szczególnie dla cech somatycznych ma decydujące znaczenie w ocenie prawidłowego rozwoju. Przyjęto, że normy powinny odzwierciedlać nie stan istniejący, lecz zalecane wartości; dlatego relacje wagowo-wzrostowe (w tym body mass index BMI) powinny być wyznaczane jedynie dla tej części populacji, w której stwierdzono prawidłową zawartość tłuszczu w ciele. Cel pracy: Wyznaczenie wagowo-wzrostowych siatek centylowych dla chłopców i dziewcząt w wieku szkolnym (7- lat). Materiał i metody: Przebadano zdrowych chłopców (n=1282) i dziewczęta (n=11) ze szkół wschodnich regionów Polski (Podlasie, Rzeszowszczyzna), u których wykonano pomiary wysokości i masy ciała oraz zawartości tłuszczu z grubości fałdów skórno-tłuszczowych metodą Slaughtera lub metodą bioimpedancji. Dane niezbędne do konstrukcji prawidłowych zakresów zawartości tkanki tłuszczowej zebrano z różnych źródeł, tak aby odpowiadały wartościom wyznaczonym dla populacji dorosłych. Wyniki: Zaproponowane normy zawartości tłuszczu posłużyły do wybrania z badanych kohort 07 chłopców (78,5%) i 581 dziewcząt (,5%), dla których opracowano siatki centylowe masy ciała należnej do wysokości ciała, jak również dla wskaźnika BMI. Wnioski: Polskie normy BMI (np. dla dzieci warszawskich lub krakowskich) różnią się między sobą. Powodem tego jest fakt, że nie uwzględniona została w nich zawartości tłuszczu w ciele, a jak wykazano szacowanie zawartości tłuszczu na podstawie BMI jest obarczone bardzo dużym błędem [AKCEP- TACJA ZMIAN]. Dodatkową zaletą siatek wagowo-wzrostowych dla populacji w przedziale 7- lat jest fakt, że podstawą oceny masy ciała nie jest wiek, jak w przypadku BMI, a jedynie wysokość ciała. Zaproponowane normy mogą być dobrym narzędziem oceny przebiegu wzrostu także w przypadkach jego zaburzeń i konieczności postępowania klinicznego i można je uznać za zalecane. sł o w a k l u c z o w e : zawartość tkanki tłuszczowej, normy wagowo-wzrostowe, wskaźnik BMI, chłopcy, dziewczęta 141

2 Stupnicki R., Tomaszewski P., Mild K. et al. Pediatric Endocrinology, Diabetology and Metabolism 09, 15, Introduction The issue of establishing reference values, especially of those pertaining to somatic features, is of importance for an assessment of normal growth. The procedure usually consists of constructing desired ranges of values determined with respect to sex, age, demographic classification, clinical criteria, etc. It is particularly desirable to create norms of body mass and fat content as both of them are fundamental in detecting obesity, as it is regarded as an important early risk factor for much of adult morbidity and mortality (1, 2). The term expected body mass means body mass appropriate for given variable, usually in relation to gender, age, body height and body proportions, the latter being commonly assessed by Body Mass Index (BMI). Body Mass Index is used to define overweight and obesity due to the ease of its use and moderate-to-high correlation with more accurate measures of body fatness (). Although the use of BMI is widely spread, its reliability has been increasingly questioned; for example, its diagnostic value for adiposity or the assessment of risk of heart attack were demonstrated to be unreliable and insufficient (4). Elevated BMI, i.e. body mass defined as obesity, refers to excessive adiposity rather than excessive weight, and because BMI does not accurately reflect body fat percentage, it is rather a surrogate for adiposity (5). Substantial discrepancies in the assessment of body fat content based on BMI brought about a lot of difficulties when determining expected body mass ranges or preparing dietary or training recommendations. Despite these drawbacks, BMI is widely used in various fields of medicine, health promotion or dietetics. Since BMI does not enable assessing body fat content with sufficient accuracy, constructing weight-height norms based on measurements obtained from a population having acceptable (normal) body fat content might offer a more rational solution. Such an approach was used in determining body mass expected for body height in schoolboys aged 8- years (6). The aim of the study The aim of this study was to present that approach in more detail, as well as the normal ranges of body mass expected for height of male and female subjects aged 7- years, designed with the use of such an approach. Material and methods The data used in this study were recorded in years in a cohort of 1282 boys and 11 girls, aged 7- years, attending randomly selected schools in the Eastern regions of Poland. Body height and mass were conventionally measured using an anthropometer and medical balance, with accuracy to 0.1 cm and 0.1 kg, respectively. Body fat content was determined by measuring thickness of skinfolds (triceps, subscapular and hip) and applying Slaughter s equation or by bioimpedance method using electronic Tanita balance (7). Since only approximate values of body fat content were needed for classification purposes, no verifying procedures were used. The data for constructing normal values of body fat content were compiled from diverse sources so as to associate them smoothly with the normal values for adults (8-). For determining the weight-height relations, body mass and body height data were converted to logarithms and the resulting allometric equations reconverted to raw units. The percentile weight/height curves were computed from values recorded in subjects having body fat content within acceptable limits, the previously published procedures were applied (11, 12). Results Body fat content of all studied boys and girls is shown in figure 1, together with the lower and upper limits corresponding to percentiles and 97, and the percentages of subjects having deficient, normal or excessive fat content in figure 2. Normal values were found in over 78% of boys and in slightly over % of girls, the difference was significant (p <0.001). Deficient body fat was found in less than % of boys and in less than 2% of girls, the difference was non-significant. The data of 07 boys and 581 girls, whose fat content was within acceptable limits, served to establish weight-height relations, i.e. body mass expected for height (MEH) and Body Mass Index (BMI). The MEH charts are presented as percentiles % 6 Fat F % at Fat F at / Chłopcy / Chłopcy Age (years) Age (years) A Wiek ge A(years) (lata) Wiek ge (years) (lata) % Fat % Fat / Dziewczęta / Dziewczęta Age (years) Age (years) A ge Wiek (years) A ge (lata) Wiek (years) (lata) Fig. 1. Body fat content in boys (n=1282) and girls (n=11) aged 7- years with lower and upper limits of the assumed normal ranges Ryc. 1. Zawartość tkanki tłuszczowej u chłopców (n=1282) i dziewcząt (n=11) w wieku 7- lat wraz z zaznaczoną dolną i górną granicą dla przyjętych wartości prawidłowych

3 Stupnicki R., Tomaszewski P., Mild K. i wsp. and the BMI ones as lower and upper limits containing the 95% area (fig. -5). Discussion Few approaches to the issue of health-related body fat content were made so far; they were usually based on the recommended BMI values (1). Since few epidemiologically founded normal body fat values are available, especially for children and youths, some literature data combined with common sense were used (14, 15). It was presumed that the ranges based on direct measurements of body fat would be more realistic than those assessed from BMI data. This led us to the view that the physiological or recommended ranges of weight-height indices, 0 % Deficient / Niedobór Normal / W normie Excessive / Nadmiar *** *** 0 / Chłopcy / Dziewczęta Fig. 2. Percentages of boys (n=1282) and girls (n=11) aged 7- years showing insufficient, acceptable or excessive body fat content Ryc. 2. Odsetek chłopców (n=1282) i dziewcząt (n=11) w wieku 7- lat o zbyt małej, prawidłowej i zwiększonej tkanki tłuszczowej 0 kg 97 / Chłopcy cm Fig.. Percentile chart of body mass expected for height (MEH) constructed for boys aged 7- years (n=07) having acceptable body fat content Ryc.. Siatka centylowa masy ciała należnej dla wysokości ciała chłopców w wieku 7- lat (n=07) o prawidłowej zawartości tkanki tłuszczowej 14

4 Stupnicki R., Tomaszewski P., Mild K. et al. Pediatric Endocrinology, Diabetology and Metabolism 09, 15, including BMI, ought to be obtained from a population having acceptable body fat content. Consistent with that view was our presumption that body fat measurements did not necessarily have to be highly accurate as they served only the purpose of eliminating subjects with roughly deficient or excessive fat content. The presented percentile norms for the weight-height relation express, in fact, the recommended values of body mass expected for height (MEH) for they were computed from data recorded in youths having acceptable body fat content. Inasmuch these norms are not superior to BMI in terms of predicting the relative body fat content, they are much easier to apply as they do not depend on age like BMI. Moreover, BMI is based on the assumption that body mass is proportional to body height raised to power 2 [cf. (16)] while in children and youths this is not true; in the presented material that exponent exceeds 2.0 in the approximate range of body height cm and exceeds.0 in the approximate range of 1-1 kg / Dziewczęta cm Fig. 4. Percentile chart of body mass expected for height (MEH) constructed for girls aged 7- years (n=581) having acceptable body fat content Ryc. 4. Siatka centylowa masy ciała należnej dla wysokości ciała dziewcząt w wieku 7- lat (n=581) o prawidłowej zawartości tkanki tłuszczowej BMI BMI 2 Chłopcy 21 Dziewczęta Age (years) 12 Age (years) Wiek (lata) 11 Wiek (lata) Fig. 5. Lower and upper limits (mean±2sd) of body mass index (BMI) computed for boys and girls aged 7 years (n=07 and 581, respectively) having acceptable body fat content Ryc. 5. Dolne i górne granice (średnia±2sd) wartości wskaźnika (BMI) wyznaczone dla chłopców (n=07) i dziewcząt (n=581) w wieku 7- lat

5 Stupnicki R., Tomaszewski P., Mild K. i wsp. cm. These norms have been made openly accessible through a website. The presented upper limits of BMI values for age, computed for children with acceptable body fat content, are remarkably, by 2 to 4 units, lower than those obtained for Warsaw children (17). This is due to the fact that the authors processed all collected data without selecting subjects according to their body fat. In view of the mounting incidence of obesity, the normal limits may become increasingly elevated even above those reported in 01, according to which the upper BMI value at the age of 16 years upwards exceeds 26 (17). Inasmuch the presented approach, compared with BMI, offers an easier evaluation of body mass in relation to body height, it ought not to be used as an estimate of body fat content. Both approaches, i.e. the presented weight-height relation and BMI, are equivalent in that respect and BMI is widely abused as an indicator of body fat. It was demonstrated that a high proportion of adults having BMI within accepted limits, i.e , have excessive body fat content and the same is true for the data presented here: 12% of boys and % of girls with normal BMI had excessive fat content (5). In conclusion, weight-height norms derived from data recorded in subjects having reasonably acceptable body fat content provide a more reliable ground for an assessment of body mass expected for given height compared with those based on non-selected data. References 2. Must A., Jacques P.F., Dallal G.E. et al.: Long-term morbidity and mortality of overweight adolescents. A follow-up of the Harvard Growth Study of 19 to 195. N. Engl. J. Med. 1992, 27, Krebs N.F., Jacobson M.S.: Prevention of pediatric overweight and obesity. American Academy of Pediatrics, Committee on Nutrition. Policy Statement. Pediatrics, 0, 112, Janssen I., Katzmarzyk P.T., Ross R.: Waist circumference and not body mass index explains obesity-related health risk. Am. J. Clin. Nutr., 04, 79, Sempolska K., Stupnicki R.: Relative fat content in young women with normal BMI but differing in the degree of physical activity. Rocz. Panstw. Zakł. Hig., 07, 58, Stupnicki R., Czeczelewski J., Tomaszewski P.: Body mass expected for body height in schoolboys. Acta Kinesiol. Univ. Tartuensis, 07, 12 (suppl.), Slaughter M.H., Lohman T.G., Boileau R.A. et al.: Skinfold equations for estimation of body fatness in children and youth. Hum. Biol., 1988,, Bodystat 10, User s guide. Body composition analysis. Bodystat Ltd., Isle of Man, Douglas, 00, Beattie resources for inclusiveness in technology and education, fitness testing for sport booklet. ACSM s Guidelines for exercise testing and prescription. 5th ed. A Waverly Company, Philadelphia, Stupnicki R., Dobosz J., Milde K. et al.: Comparative analysis of age-dependent processes. Papers Anthropol., 0, 12, Stupnicki R., Milde K., Przewęda R.: Constructing growth reference curves. Papers Anthropol., 01,, Gallagher D., Heymsfield S.B., Heo M. et al. Healthy percentage body fat ranges: an approach for developing guidelines based on body mass index. Am. J. Clin. Nutr., 00, 72, Higgins P.B., Gover B.A., Hunter G.R., Goran M.I.: Defining health-related obesity in prepubertal children. Obes. Res., 01, 9, Neovius M.G., Linné Y.M., Barkeling B.S. et al.: Sensitivity and specificity of classification systems for fatness in adolescents. Am. J. Clin. Nutr., 04,, Franklin M.F.: Comparison of weight and height relations in boys from 4 countries. Am. J. Clin. Nutr., 1999, (suppl.), 157S-162S. 17. Palczewska I., Niedźwiecka Z.: Somatic development indices in children and youth of Warsaw. Develop. Period Med. 01, 5 (suppl. 1), Freedman D.S., Dietz W.H., Srinivasan S.R. et al.: The relation of overweight to cardiovascular risk factors among children and adolescents: the Bogalusa heart study. Pediatrics, 1999,, Received: xxx-xx-xx. Accepted: xxxx-xx-xx. Konflikt interesów: nie zgłoszono 145