Thinness, overweight and obesity in indigenous youth in Oaxaca, 1970 and 2007
Delgadez, sobrepeso y obesidad en jóvenes indígenas en Oaxaca, 1970 y 2007
Robert M Malina, PhD,(1,2) María Eugenia Peña-Reyes, PhD,(3) Guillermo Bali-Chávez, PhD,(4) Bertis B Little, PhD.(5)
(1) Department of Kinesiology and Health Education, University of Texas. Austin, Tx, USA.
(2) Department of Kinesiology, Tarleton State University. Stephenville, TX, USA.
(3) Escuela Nacional de Antropología e Historia, Instituto Nacional de Antropología e Historia. México, DF.
(4) Comisión Nacional para el Desarrollo de los Pueblos Indígenas. México, DF.
(5) Departments of Mathematics, Physics, and Engineering, and Academic Affairs, Tarleton State University. Stephenville, TX, USA.
Objective. To evaluate change in body mass index (BMI) and weight status of indigenous youth in Oaxaca between the 1970s and 2007.
Materials and methods. Heights and weights were measured in cross-sectional samples of school children 6-14 years in the 1970s (2 897) and 2007 (4 305); BMI was calculated. International Obesity Task Force cutoffs for weight status were used. BMI and prevalence of severe and moderate thinness, overweight and obesity were compared by year.
Results. BMI increased significantly across time. Primary change in weight status occurred in overweight, 1970s, <2%; 2007, 7 to 12%. Little change occurred in thinness (<2%) and obesity (≤1%) in both surveys, except in children 6-9 years (obesity=4% in 2007).
Conclusion. BMI and prevalence of overweight increased across all ages from the 1970s to 2007, but children 6-9 years appeared to be more at risk for obesity than youth 10-14 years. Prevalence of thinness was unchanged.
Key words: prevalence; growth; children; adolescents; Mexico.
Objetivo. Evaluar el cambio en el índice de masa corporal (IMC) y el estatus de peso entre 1970 y 2007 en jóvenes indígenas de Oaxaca.
Material y métodos. Se midieron estatura y peso de series transversales de escolares indígenas en edades de 6 a 14 años en 1970 (2 897) y en 2007 (4 305), se calculó el IMC y se emplearon los puntos de corte del International Obesity Task Force para el estatus de peso. El IMC y la prevalencia de delgadez, sobrepeso y obesidad en 1970 y 2007 fueron comparados.
Resultados. El IMC aumentó de manera significativa entre 1970 y 2007. Los cambios más importantes fueron en sobrepeso, <2% en 1970 a 7-12% en 2007. Hubo poco cambio en la delgadez (<2%) y la obesidad (≤1%) en ambas investigaciones, excepto en niños de 6 a 9 años (4% en 2007).
Conclusión. El IMC y la prevalencia de sobrepeso aumentaron a través de todas las edades de los años 1970 a 2007, pero los niños de 6 a 9 años parecen tener un mayor riesgo para la obesidad que los jóvenes de 10 a 14 años. La frecuencia de la delgadez fue igual.
Palabras clave: prevalencia; crecimiento; niños; adolescentes; México.
Increased prevalence of overweight and obesity among Mexican youth1-6 is consistent with the global epidemic. Prevalence in Mexico was lowest among children 5-11 years in the southern region, which includes Oaxaca, and rural areas.3-5 Estimates for Oaxaca youth in 2006 were among the lowest in all Mexican states.7 Overweight and obesity were also less prevalent in households in which women <50 years spoke an indigenous language.4
Our previous studies in Oaxaca have considered change in overweight and obesity in a rural indigenous community in the central valley between 1968, 1978 and 20008 and in a colonia of Oaxaca de Juárez between 1972 and 2000.9 Overweight and obesity were not common among youth in 1968-1978, but overweight and to a lesser extent obesity increased in 2000. This report extends our observations to indigenous youth in four regions of Oaxaca. It specifically evaluates change in the BMI and prevalence of thinness, overweight and obesity in indigenous school youth 6-14 years between the 1970s and 2007. Oaxaca has the largest indigenous population in Mexico and includes at least 15 different linguistic groups.10
Materials and methods
The growth status of 2897 (1419 boys, 1478 girls) school youth 6-14 years of age in 18 communities in four regions of Oaxaca (Central Valley, Sierra South, Sierra Northeast, Isthmus) was surveyed in 1971, 1972, 1977 and 1978.* Surveys were set in the context of nutritional anthropology and conducted in collaboration with ethnographic studies. Grant support for surveys in 1971, 1972 and 1978 implied approval by the University of Texas at Austin (see Acknowledgements); formal institutional review committees were not established at the time of the surveys.‡,11 Officials (president and council, school principal) in each community also approved the surveys. Surveys in 1977 were done at the request of Instituto Nacional para el Desarrollo de la Comunidad y de la Vivienda Popular (INDECO). Institute personnel obtained approval from community and school officials.
The 18 communities represented the Central Valley (10), Sierra South (5), Sierra Northeast (2) and Isthmus (1). All rural communities were indigenous. The two colonias were populated primarily by indigenous migrant families from rural areas of the state.
Permission for participation of the children was thus granted by the president and his council, and school principal in each community. Surveys were done at the schools. Children were free to choose to participate or not participate. The sample thus represented children in attendance on days of the surveys. Individual identities were blinded in all analyses.
The data for 2007 are for youth 6-14 years enrolled in bilingual schools, albergues escolares.12-14 The sample was based on a double cluster and stratified design. Criteria for attendance at albergues schools were membership in an indigenous community, speak/understand an indigenous language, registration at a public school, and unstable home conditions.13 The latter included children who did not live with their parents, children with a mother or father who had emigrated, and/or children from families with some degree of dysfunction. Height and weight were measured as part of the health and nutrition monitoring program. Data were provided by the albergues directorate, and are presently restricted for research or implementation of public policies. Individual identities of the children were blinded. The present analysis is limited to 4 305 youth (2 368 boys, 1 937 girls) from 58 municipios located in the same regions surveyed in the 1970s: Central Valley (6), Sierra South (24), Sierra Northeast (17) and Isthmus (11).15
Height was measured with a field anthropometer to the nearest 0.1 cm in the 1970s, and weight with a portable scale to the nearest 0.5 pound (converted to kg). Children wore light clothing with shoes and accessories removed. Inter- and intra-observer technical errors of measurement for height were 0.20 to 0.54 cm and 0.33 to 0.38 cm, respectively.10 Replicate weights were not measured. Heights and weights in 2007 were measured by trained albergues staff following the U.S. Centers for Disease Control and Prevention protocol.15
The body mass index (BMI, kg/m2) was calculated. Ages were extracted from school records. Sex- and age-specific BMI criteria of the International Obesity Task Force (IOTF) were used to define overweight and obesity,16 and severe and moderate thinness.17 Comparative data for Mexico also used these criteria.7
Age- and sex-specific means and standard deviations for BMI were calculated for the 1970s and 2007. Sex-specific multiple analyses of covariante (MANCOVA), controlling for age, were used to compare BMIs across years in two age groups: 6-9 (childhood) and 10-14 (early- and mid-adolescence). Prevalence of severe and moderate thinness, overweight and obesity was calculated for the two sex-specific age groups by year and compared with Chi square. The Statistical Package for the Social Sciences (SPSS version 14.0) was used. Significance was set at p<0.05.
Descriptive statistics for BMI by age and sex are summarized by year in Table I. Comparisons of sex-specific age groups across time are shown in table II. BMIs are significantly higher in 2007 compared to the 1970s. Secular increases are larger in older than younger children. Lack of overlap of 95% CIs suggests a significantly larger increase in older than younger boys, but 95% CIs overlap somewhat between age groups of girls. Estimated rates of secular gain in BMI over approximately 3.2 decades are 0.34 and 0.36 kg/m2 per decade in boys and girls 6-9 years, respectively, and 0.48 and 0.47 kg/m2 per decade in boys and girls 10-14 years, respectively.
Prevalence of severe and moderate thinness is low and does not differ between surveys (table III). Overweight is low in the 1970s but increases in both age groups and sexes in 2007 (p<0.001). Obesity is largely absent in the 1970s, but increases to 3.7% and 3.9% in boys and girls 6-9 years, respectively, in 2007 (p<0.001). Obesity among youth 10-14 years, though significantly higher in 2007 (p<0.05), is <1%.
BMIs of indigenous Oaxaca school children increased significantly between the 1970s and 2007. Compared to U.S. reference values18 mean BMIs of boys and girls in the 1970s were at the medians at 6-7 years and shifted toward the 25th percentiles (P 25) by 11 years; BMIs of boys remained at P 25 while those of girls reached the median at 13-14 years. In 2007, mean BMIs of boys and girls were at 75th percentiles (P 75) at 6-7 years, and shifted towards the reference medians between 8 and 11 years. At 12-14 years, BMIs of indigenous girls moved towards P 75 while those of boys remained close to the medians. Both height and weight increased significantly in the indigenous children between the 1970s and 200719 and contributed to the gains in BMI over the interval of about 32 years (assuming 1975 as the 1970s midpoint).
Rural communities surveyed in the 1970s depended on subsistence agriculture, but several also produced cheese, poultry and crafts and few had regional market activities.10 Colonia residents depended on occupational resources in the capital. Elevated infant and preschool mortality in Oaxaca in the 1970s suggested marginal health and nutritional conditions in the rural areas and colonias.10,20 Living and nutritional conditions in the respective communities have presumably improved over time in association with economic growth and land reform and in turn contributed to secular improvement in growth status of the indigenous children.19-22
The major change in weight status of indigenous school youth between the 1970s and 2007 occurred in overweight which increased significantly from <2% to 12% in boys and girls 6-9 years and girls 10-14 years, and to 7% in boys 10-14 years (table III). Prevalence of severe and moderate thinness was low and did not change across time. Obesity was present in <1% of youth in the 1970s. It increased to ~4% in boys and girls 6-9 years in 2007 but remained <1% in boys and girls 10-14 years. Indigenous children 6-9 years thus appeared more at risk for obesity than older youth.
Prevalence of overweight and obesity among indigenous children 6-9 years in 2007 was reasonably similar to estimates for Oaxaca children 5-11 years (indigenous and non-indigenous) in the 2006 National Health and Nutrition Survey.7 On the other hand, overweight and obesity among indigenous youth 10-14 years in 2007 were less prevalent compared to Oaxaca youth 12-17 years in the 2006 survey.
The albergues schools provided meals daily and some provided rooms Monday to Friday. School meals followed the directive of the Ministry of Health for "el plato de bien comer" which included three food groups: green vegetables and fruits; cereals; and legumes and foods of animal origin. The diet aimed to normalize nutritional deficiencies (milk fortified with iron, zinc, folic acid and vitamins) and incorporate local vegetables and fruits.23,24 A regular and improved diet at the schools may have contributed to the secular gain in weight-for-height reflected in the BMI.
Detailed observations for a single rural Zapotec-speaking community indicated little dietary variety, limited sources of animal protein, and dependence upon corn in the form of tortillas and beans at the household level in 1968 and 197825 but greater variety and increased consumption of animal protein in 2000.20 Soft drinks were noted in 5% of households in 1968, 26% in 1978 and 36% in 2000.20,25 Corresponding data for Oaxaca households were 21% in 1996 and 23% in 2006.26
Reduction in habitual physical activity is often indicated as contributing to the current epidemic of obesity. Subsistence agriculture required regular moderate-to-vigorous and periodically vigorous physical activity in adult males and boys (when school was out). Women and girls were also involved at some times of the year, specifically harvest. Youth 9-17 years in a rural Zapotec community in 2000-2002 spent about 2 hours per day on household chores which were moderate-to-vigorous and vigorous in boys and moderate or moderate-to-vigorous in girls.27 Children 6-8 years and youth 9-17 years also walked, respectively, an estimated 2 364±1 125 (median 2 249) and 2 605±1 176 (median 2 650) steps per day to and from school, and had one hour per week of required physical education.27,28 The majority of youth (~85%) also reported regular participation in sport, soccer (boys) and basketball (both sexes). Assuming reasonably similar conditions in other indigenous communities, lifestyles of rural youth probably involved regular physical activity. In contrast, only 35% and 24% of Mexican youth 10-19 years (sexes combined) in the 2006 National Health and Nutrition Survey were physically active (7 hrs/week in moderate or vigorous activity) and moderately active (4-6 hrs/week), respectively, while 40% were inactive.29
Television viewing was a major sedentary leisure activity for Zapotec youth, 2.1±1.5 hrs/day in our 2000-2002 field survey (only five boys and no girls reported playing video games),27 which was about one-half of reported screen time (television, games, videos) in Mexico City youth.30,31 Televisions increased from 31% to 58% in rural Oaxaca households between 1996 and 2005.26 Increased availability of appliances and reduction in agriculture as the primary subsistence activity and in the percentage of households raising animals, fruits and vegetables declined between 1996 and 2005. Overall, changes at the household level enhanced the potential for reduction in physical activity in rural areas of Oaxaca.
Two concerns are inherent to comparisons across time, measurement protocols and population comparability. Height and weight are standard measurements in surveys of growth and nutritional status. The first author (RMM) trained technicians in anthropometry for the U.S. National Health Examination of youth 12-17 years in the 1960s; the same protocol was used in our surveys in the 1970s. Techniques used in the U.S. were also used in the indigenous schools. It is thus reasonable to assume measurement techniques in the 1970s and 2007 were similar.
The sample in the 1970s included all children in attendance at schools in 18 communities at the time of the surveys in 1971, 1972, 1977 and 1978. School children in 2007 represented a stratified random sample of children attending albergues schools in the state of Oaxaca, although only those attending schools in the same four regions as in the 1970s were used. The 2007 sample is perhaps more representative of indigenous school children than the 1970s sample, thus limiting comparisons of weight status across two time points to some extent. However, consistency of measurement protocols in the 1970s and 2007 and the relatively large samples should serve to offset potential sampling bias. Several other considerations also highlight comparability of the samples. All were from indigenous communities in the same regions of Oaxaca (except for two colonias). The majority were from Zapotec-, Mixtec- and Mixe-speaking communities, ~80% (1970s) and ~83% (2007). Although indigenous groups of Oaxaca are linguistically and to some extent culturally isolated, they are rather homogeneous genetically.32 The Zapotec, Mixtec and Mixe also form a closely related genetic cluster distinguished from other populations in Mexico and Central America.33-35 Other indigenous groups from Oaxaca were not represented in the latter analyses.
In summary, changes in the BMI over ~3 decades between the 1970s and 2007 were reflected in a significant increase in overweight in indigenous school youth 6-9 and 10-14 years. Prevalence of thinness in both age groups and obesity in youth 10-14years was low and did not change. By inference, change in energy intake and/or physical activity (energy expenditure) was not sufficient to trigger a major increase in obesity. However, ~4% of indigenous children 6-9 years in 2007 were obese, which suggests that the signal for obesity may be incipient in younger children.
Research in the 1970s was funded in part by National Science Foundation grants GZ 1906 (1971) and BNS 78-10641 (1978-1980), and the Institute of Latin American Studies at the University of Texas at Austin. The assistance of Professors Arthur D. Murphy and Henry A. Selby in facilitating the surveys in the 1970s is acknowledged and greatly appreciated.
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Received on: September 14, 2012
Accepted on: April 15, 2013
Robert M. Malina, PhD.
10735 FM 2668, Bay City, TX 77414 USA.
Declaration of conflict of interests: The authors declare not to have conflict of interests.
*Malina RM, Peña-Reyes ME. Estatus de crecimiento en niños escolares del estado de Oaxaca: Resultados de encuestas realizadas en 18 comunidades en la década de 1970. México, DF. Instituto Nacional de Antropología e Historia: (in press).
‡Institutional review boards were not established until after the 1979 Belmont Report from the Department of Health, Education, and Welfare.11