The prevalence of overweight is increasing among all Americans (Kuczmarski et al. 1994). Among the Navajo, the increase has been rapid within the past 40 years. In 1953, the prevalence of overweight was <5% among men and only 15% among women between the ages of 15 and 45 y in a survey of two Indian Health Service (IHS)⁴ service units (Sandstead et al. 1956). By 1979, 24% of Navajo men and 51% of Navajo women weighed 110% or more of the optimal weight for height according to the 1959 Metropolitan Life Insurance tables (DeStefano et al. 1979). In 1989, clinical impressions of IHS health care providers that heights, weights and the prevalence of overweight were increasing among Navajo school children were substantiated by a school survey (Sugarman et al. 1990b). Explanations for the increased prevalence of overweight among the Navajo over the past 40 years focus on the increased abundance of calorie-dense foods and decreased levels of physical activity (Broussard et al. 1991, Sugarman et al. 1990b, Welty et al. 1991). In addition, it has been suggested that the native peoples of the Southwest may have unique metabolic characteristics, conditioned by genetic factors, that predispose them to rapid and excessive weight gain (Knowler et al. 1983, Ravussin 1993).

The Navajo Health and Nutrition Survey provided the first opportunity to assess the prevalence of overweight in a large, population-based sample of the Navajo Nation. In this paper, we present data on weight, anthropometric dimensions, attitudes about weight and weight management practices of Navajo adults. Other papers in this volume explore weight in adolescents (Freedman et al. 1997) and the association of weight with specific chronic diseases (Mendlein et al. 1997, Percy et al. 1997, Will et al. 1997)

MATERIALS AND METHODS

An intensive 40-h training course was held to teach proper procedures for conducting the survey, including the anthropometric measurements. Staff from the third National Health and Nutrition Examination Survey (NHANES III) conducted by the National Center for Health Statistics of the Centers for Disease Control and Prevention provided anthropometry training. Follow-up training sessions were held during the course of the survey, and staff were observed several times during interviews to ensure that they adhered to the standard protocols and methods.

Anthropometric measurements taken during the survey included standing height; weight; triceps, suprailiac and subscapular skinfolds; and waist and hip circumferences. Independent duplicate measurements were made at all sites by a team of two interviewers using the standard protocols of the NHANES III (McDowell et al. 1985). Height was measured without shoes to the nearest 0.1 cm using portable stadiometers (Shorr Productions, Woonsocket, RI). Weight was measured without shoes or heavy outer clothing and recorded to the nearest 0.1 kg using calibrated digital scales (model 770, Seca, Columbia, MD). Skinfolds were measured to the nearest 0.5 mm with calibrated Lange skinfold calipers (Cambridge Scientific Instruments, Cambridge, MD). Circumferences were measured over light clothing with steel tapes to the nearest 0.1 cm. Because many dwellings had carpeted or uneven floors, or ceilings shorter than the stadiometers, some measurements had to be made outside on plywood platforms.

The mean of the two measurements was used in this analysis. For all but the suprailiac skinfold measurements, the mean difference between the duplicate measurements was <1%; for the suprailiac skinfold, the measurements differed by an average of 3%. Twelve percent of the participants declined duplicate skinfold measurements and 33% of the participants declined duplicate waist and hip circumferences. Because the duplicate measurements agreed so closely among other participants, for those participants with only one measurement of a dimension, the single measurement was used in analysis. Measurements of pregnant women (n = 35) were excluded from analysis. Information on adolescents (age 12-19) is presented separately (Freedman et al. 1997).

The prevalence of overweight was assessed using body mass index (BMI, kg/m²). Overweight was defined as a BMI > the 85th percentile of the Second National Health and Nutrition Examination Survey (NHANES II) reference data for men and women age 20-29 (BMI > 27.8 and BMI > 27.3, respectively; National Center for Health Statistics 1987). This definition of overweight is the reference value for the Year 2000 Objectives for weight management for the U.S. population as a whole and for American Indians and Alaskan Natives (U.S. Public Health Service 1991). Appropriate weight was defined as BMI between the 15th and 84th percentiles, inclusive; underweight was defined as BMI < 15th percentile (BMI < 20.8 for men, BMI < 19.1 for women).

Participants' attitudes about their own weight were assessed by asking them to classify themselves as underweight, appropriate or overweight. Ideal body types were determined by having participants select one of five silhouettes depicting men or women of different weight status (Fig. 1). The silhouettes were modified from those published by Zellner et al. (1989) to have Navajo hairstyles and general body type. Silhouette 1 is extremely thin, Silhouette 2 is slender, Silhouette 3 is intended to be neither overweight nor underweight, Silhouette 4 is slightly overweight and Silhouette 5 is markedly obese. Participants were asked to indicate which silhouette represented the weight they believed was the healthiest. Participants were asked if they were trying to lose weight, and if so, what methods they were using.

We present mean values for anthropometric dimensions by sex and age group. Comparisons of continuous variables were made by t tests and ANOVA; chi-square tests were used to assess distributions of categorical variables. Sample weights were assigned according to the sampling design described by White et al. (1997), and analyses were performed with SUDAAN software (Shah 1991) to take into account the complex sample design.

RESULTS

Table 1. Anthropometric dimensions of adult participants in the Navajo Health and Nutrition Survey, 1991-1992 [View Table]

Table 2. Distribution of body mass index1 categories among adult participants in the Navajo Health and Nutrition Survey, 1991-1992 [View Table]

Among both men and women, height was greatest among 20- to 39- y-olds and lowest among those over 60 (Table 1). Weight, BMI, skinfolds and waist circumference were greatest in participants age 40-59 and lowest in participants age 60 and older, although not all of the differences were statistically significant. Among men, the prevalence of overweight was 37% among 20- to 39-y-olds, 50% among 40- to 59-y-olds, and only 9% among men age 60 and older (Table 2). Among men, the prevalence of underweight was 7% for men age 20-39 and age 40-59, but 15% for men age 60 and older. Two thirds or more of the women in each age group were overweight. Among women, the prevalence of underweight was 3% or less in all age strata.

More than one third of the participants misclassified their weight status (underweight, appropriate, overweight) relative to their BMI category. Nineteen percent underestimated their weight status relative to their BMI category, i.e., they believed they were thinner than their BMI classification; and 17% overestimated their weight status relative to BMI, or believed themselves to be fatter than their BMI classification. Women overestimated their weight status more frequently than men (21 and 17%, respectively, P < 0.05) and participants age 20-39 overestimated their weight status more frequently than older participants (21, 13 and 11% for ages 20-39, 40-59, and 60+, respectively, P < 0.001).

Among participants <60 years old, 14% of men and 7% of women chose one of the two heavier silhouettes as the healthiest (Fig. 2), but among participants age 60 and older, 31% of men and 17% of women chose the heavier silhouettes. The age difference in silhouette preference among men reflects a simple tendency to prefer the heavier silhouettes at the expense of the thinner ones. Among women, the situation is more complex. Although more older than younger women chose the two heaviest silhouettes as ideal, the majority (52%) of women age 60 and older preferred the thinner two silhouettes, as did women age 40-59. The age group differences were significant for both sexes (P < 0.001). Men chose the heavier silhouettes more often than women (P < 0.001). The sex and age group differences in silhouette preference were statistically independent.

Overall, 43% of the participants reported that they were trying to lose weight. Women reported trying to lose weight more often than men (Table 3). Among both men and women, trying to lose weight was most common among participants age 20-39, less common among participants age 40-59 and least common among participants age 60 and older. Among participants age 20-39 and those age 60+, women reported trying to lose weight more often than men. Trying to lose weight was most common among those overweight and least common among those underweight; one fourth of men and one third of women of appropriate weight reported trying to lose weight.

Table 3. Self-reported efforts to lose weight among adult participants in the Navajo Health and Nutrition Survey, 1991-1992 [View Table]

Among participants trying to lose weight (n = 334), 82% reported currently using diet and exercise. Only 3% said that they were using diet pills, 3% said that they were using other special products (laxatives, diuretics, meal substitutes), and 4% said that they vomited after eating. However, 19% of those trying to lose weight said that they fasted 24 h or more at least occasionally for weight control. Twenty-three percent of the participants trying to lose weight reported currently using one or two weight loss methods in addition to diet and exercise. There were no differences by sex, age group or BMI category in the frequency of weight control methods reported.

DISCUSSION

We have presented tabulations of subscapular and triceps skinfolds, waist and hip circumferences, and their ratios. Because only limited comparative data for these dimensions exist from previous studies among the Navajo (Hall et al. 1991), we have no basis for assessing changes in the means or distributions of these dimensions over time for the Navajo. We anticipate that these data will provide a base line for future monitoring and surveillance. The associations among these measurements and other risk factors in the Navajo are explored in other papers of this volume (Mendlein et al. 1997, Percy et al.1997, Will et al. 1997).

More than one third of the participants in this survey misclassified their own weight status relative to their BMI categories. The self-perception of weight and attitudes about appropriate weight varied by sex and age group among the Navajo. Participants age 60 and older, especially men, chose overweight images as ideals of health more often than younger participants. This is consistent in part with a previous report of Crosby et al. (1991), who found that Navajo men and women over age 60 prefer heavier body types, whereas those under age 60 prefer more moderate body types. Crosby's results and ours are also consistent with impressions of the IHS staff that older Navajo clients believe that moderate overweight is normal and healthy. Attitudes about weight in general and about one's own weight in particular may be changing among younger Navajo, and may differ by sex, because participants under age 40 and women believed they were overweight and reported trying to lose weight more often than older participants and men.

The cross-sectional design of this study is adequate for estimating prevalence but does not contribute any direct information about the development of overweight among the Navajo. In particular, it was impossible to determine whether the low BMI values among men age 60 and older occur because they have been thin all their lives (a cohort effect) or because overweight men were more likely to die at earlier ages (a survivor effect). We do not believe that the apparently low prevalence of overweight among elderly men is due to inadequate representation because men age 60 and older were in fact slightly overrepresented in our sample relative to the census population of the Navajo (White et al. 1997).

Height, weight and the prevalence of overweight have been increasing among Navajo children (Sugarman et al. 1990b) and overweight is now common among young adult Navajo. Many adolescents in this sample were overweight (Freedman et al. 1997) and, within the limits of the cross-sectional nature of the data now available, it appears that excessive weight gain begins for many Navajos in childhood. Among the Navajo, increases in overweight parallel increases in chronic diseases such as diabetes (Sugarman et al. 1990a, Will et al. 1997), hypertension (DeStefano et al. 1979, Percy et al. 1997), and cardiovascular disease (Sugarman et al. 1990a, Mendlein et al. 1997) over the past four decades. Overweight is now common among the Navajo, and among older and more traditional Navajo, it may be viewed as normal. In contrast, among younger adult Navajo, attitudes about weight may be changing. Educating people about appropriate body weight, preventing the onset of overweight and controlling body weight throughout life are essential to reducing the burden of chronic disease among the Navajo. This will require primary prevention directed at reducing the prevalence of childhood overweight as well as weight management programs for adults. More systematic preventive programs are needed in schools to effectively address this problem at the earliest possibly opportunity. Prenatal and well-baby clinics should also be targeted for intervention programs. In view of the limited success of weight reduction programs for overweight children and adults, primary prevention may prove to be a more effective public health initiative.

ACKNOWLEDGMENTS