1 Applied Research Program, National Cancer Institute, Rockville, MD.
2 Karolinska Institutet, Family Medicine Stockholm, Novum, Huddinge, Sweden.
3 Stanford Center for Research in Disease Prevention, Stanford University School of Medicine, Palo Alto, CA.
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ABSTRACT |
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acculturation; cardiovascular diseases; diet; emigration and immigration; Mexican Americans; nutrition; primary prevention
Abbreviations: CVD, cardiovascular disease; FFQ, food frequency questionnaire; NHANES III, Third National Health and Nutrition Examination Survey; SES, socioeconomic status
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INTRODUCTION |
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Changes in diet often occur when groups of people migrate or become more acculturated, which may influence their levels of risk factors for CVD (7). For example, subgroups of the Hispanic population show distinct differences in dietary intakes according to country of birth (8
, 9
), generational status (10
), and primary language spoken (11
). In general, Hispanics born in the United States eat diets higher in fat and lower in fiber compared with Hispanics born outside the United States. Moreover, Hispanics who have lived in the United States for more than one generation or who are more acculturated (defined as speaking English) report higher average intakes of fat and lower average intakes of fiber than first-generation Hispanics who have stronger ties to their traditional culture. Previous studies (9
, 10
, 12
, 13
), however, have not shown consistent patterns of vitamin and mineral intakes among the different subgroups of Hispanics. These studies also have been limited by small sample sizes (9
) or restricted geographic areas (11
13
) or have included only women (9
, 10
); thus, they fail to represent the overall US population. Furthermore, they have not examined level of acculturation by both country of birth and primary language spoken to further differentiate Hispanics living in the United States today.
Socioeconomic status (SES) often accounts for ethnic differences in CVD risk factors, including factors related to dietary intake (1416
). However, diet studies of Hispanic populations that have analyzed SES report inconsistent findings. For example, the San Antonio Heart Study showed that Hispanic men living in higher SES neighborhoods had higher fat intakes than Hispanic men living in lower SES neighborhoods (17
). In contrast, the San Luis Valley Diabetes Study showed that Hispanics whose SES was higher (as measured by number of years of education) had lower fat intakes than Hispanics whose SES was lower (18
). Unfortunately, past studies of diet and health that used US samples have not clarified these inconsistent findings, possibly because they have not accounted for differences in SES.
In the present study, we analyzed dietary data on 2,853 Mexican-American women and men from the Third National Health and Nutrition Examination Survey (NHANES III) who were differentiated according to country of birth and primary language spoken: those born in Mexico, those born in the United States whose primary language was Spanish, and those born in the United States whose primary language was English. Our first objective was to compare intakes of energy and nutrients related to CVD from 24-hour dietary recalls among the three groups of Mexican Americans, after adjusting for age and SES (as measured by years of education). Our second objective was to determine to what degree each group met the nationally recommended intakes for dietary fat, fiber, and selected vitamins and minerals. Our last objective was to compare the frequencies of intake of foods reported on a 1-month food frequency questionnaire (FFQ) among the three groups and to evaluate these qualitative results in relation to the quantitative nutrient intakes determined from 24-hour dietary recalls.
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MATERIALS AND METHODS |
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Study sample
The sample for our analyses included 1,449 Mexican-American women and 1,404 Mexican-American men aged 2564 years who completed both the home questionnaire and medical examination. We used age 25 years as our lower age cutpoint because educational attainment (a covariate in our multivariate regression models) often is not complete before this age. Age 64 years was used as our upper age cutpoint to avoid problems regarding selection effects due to non-CVD-caused morbidity and mortality (22). We excluded data for respondents who were pregnant (n = 63), those for whom education information was lacking (n = 20), and those whose surveys were coded as unreliable (n = 2). In our analyses of energy and nutrient intakes, we excluded an additional 141 subjects whose 24-hour dietary recalls were coded as unreliable and 50 subjects who reported consuming less than 500 or more than 5,000 total calories. Respondents who were excluded represented the three Mexican-American groups defined below.
Definition of variables
Race/ethnicity was based on asking respondents to classify their ethnicity as Black; Mexican or Mexican American; White, non-Hispanic; Asian or Pacific Islander; Aleut, Eskimo, or American Indian; or other Latin American or other Spanish. Respondents who chose Mexican or Mexican- American ethnicity were included in our analysis. Migration status and level of acculturation were indicated, respectively, by country of birth and primary language spoken at home, both factors that have shown high levels of validity and reliability (23) and that reflect the strength of cultural beliefs and practices and influence health status (24
). To explore whether dietary patterns differed according to migration status, level of acculturation, or both, we divided the respondents into three groups: those born in Mexico, those born in the United States whose primary language spoken at home was Spanish, and those born in the United States whose primary language spoken at home was English.
Information on educational attainment was collected as a continuous variable and was defined as the highest number of years of education completed. We chose years of education as our measure of SES because few data tend to be missing, it remains valid throughout adulthood, and it is available for persons not employed outside the home (25).
Measurement of diet
Nutrient and food intakes were assessed for the three groups of Mexican-American women and men by using a single 24-hour dietary recall and a 1-month qualitative FFQ. The 24-hour dietary recall was administered by bilingual Spanish-speaking interviewers at the mobile examination centers; an automated, interactive interview and coding system were used that featured a standardized interview format and automated probes to obtain detailed information about foods, including brand names, preparation methods, and ingredients used in preparation (26). Three-dimensional food models, measurement aids, and food-specific units were used to estimate amounts consumed. Not included were nutrients obtained from nutritional supplements, medications, and seasonings added to prepared foods at the table. From the 24-hour dietary recall, we determined total calories, percentage of calories from total fat and saturated fat, and the following nutrients: cholesterol, fiber, vitamin A, vitamin C, vitamin E, folate, vitamin B6, calcium, potassium, and magnesium. These nutrients were selected because of their association with CVD (27
29
).
The FFQ, administered during the household interview, was used to ask respondents about the average number of times foods were eaten during the 1-month period preceding the interview date. Frequencies of consumption of foods from the following food groups were ascertained: milk and milk products, meat and egg dishes, fruits and fruit juices, vegetables, grains and legumes, desserts, and added fats.
We also determined the percentages of respondents, by migration status and level of acculturation, who met the US dietary guidelines (3032
) or recommended intakes of selected nutrients (33
35
). Dietary guidelines included total fat (
30 percent kcal/day), saturated fat (<10 percent kcal/day), cholesterol (
300 mg/day), fiber (
25 g/day), and potassium (
3,500 mg/day). Intake of vitamin A was compared with the Recommended Dietary Allowances (33
); vitamin C, vitamin E, folate, vitamin B6, calcium, and magnesium were compared with the Dietary Reference Intakes (34
, 35
). Percentages of Mexican Americans who reported taking a vitamin or mineral supplement in the past month were also determined from a question asked during the household interview.
Statistical analysis
Primary analyses, using multiple linear regression models, were carried out with SUDAAN software (version 7.11; Research Triangle Institute, Research Triangle Park, North Carolina) to adjust for the complex sample design of NHANES III (19). All analyses incorporated sampling weights that adjusted for unequal probabilities of selection. Multivariate analyses were conducted separately for men and women. The dependent variables were energy and nutrient intakes. The independent variables were the three migration and acculturation groups (Mexican born, US-born Spanish speaking, and US-born English speaking), educational attainment (in years, centered at the sample mean for each gender to aid in interpretation of the regression coefficients), age (centered at the sample mean for each gender), and their first-order interactions.
The SAS System for Windows (version 6.12; SAS Institute, Cary, North Carolina) was used to determine the frequencies of various demographic characteristics, percentages of persons who met the dietary guidelines or recommended intakes of nutrients or who took a vitamin or mineral supplement, and frequencies of foods and food groups reported from the FFQ by the three groups of Mexican Americans. Sampling weights also were incorporated in these analyses.
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RESULTS |
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The least-squares means, adjusted for education, age, and all first-order interaction terms, are presented in table 3. Differences in folate and calcium intake appear particularly clinically significant between Mexican-born and US-born women and men. With the exception of vitamin A, no significant differences in nutrient intakes were found between Spanish-speaking and English-speaking US-born Mexican Americans. Similar results were found when nutrient densities, as measured by nutrient intakes per 1,000 calories, were compared among the three groups of women and men.
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DISCUSSION |
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One possible explanation for the lack of differences in diet according to primary language spoken may be that all persons in the United States are similarly exposed to food advertising and food choices from the time they are young. Past research provides evidence that food choices made during childhood influence food choices made during adulthood (36). In contrast, lack of exposure to Americanized dietary habits during childhood may have contributed to the healthier diets of Mexican Americans born in Mexico, most of whom came to the United States as adults.
Comparison to other research
In general, we found that women and men born in Mexico consumed significantly fewer calories from total and saturated fat and significantly more fiber, vitamin A, vitamin C, vitamin E, folate, vitamin B6, calcium, potassium, and magnesium, after accounting for education and age, than did US-born Mexican-American women and men. Our energy and nutrient results, with the exception of dietary cholesterol, agree with findings from the few studies that have evaluated the diets of Hispanics or Mexican Americans by country of birth, generational status, or primary language spoken (911
). In other studies (9
, 10
), cholesterol intake was significantly higher in first-generation Mexican- American women. In our study, only men born in Mexico reported a significantly higher cholesterol intake compared with US-born men.
Our results differ from those of the San Antonio Heart Study and the San Luis Valley Diabetes Study. For example, in contrast to our study, calcium and potassium intakes were lowest among the poorest Mexican Americans in the San Antonio Heart Study (12) and did not differ by educational level among Hispanics in the San Luis Valley Diabetes Study (13
). These inconsistent findings are possibly due to the different ways in which Hispanics were compared (by migration status and primary language spoken in our study, by neighborhood income in the San Antonio Heart Study, and by years of education in the San Luis Valley Diabetes Study). Although Balcazar et al. (37
) have shown that language spoken and years of education are correlated (r = 0.21), some Hispanics who predominantly speak Spanish are highly educated while some Hispanics who predominantly speak English have little education. Thus, studies that compare Hispanics by using only one characteristic (e.g., country of birth), without adjusting for others (e.g., primary language spoken, years of education), may not differentiate this population clearly.
As we found for nutrient intakes, a greater proportion of Mexican-born than US-born Mexican-American men and women met the dietary guidelines for total fat, saturated fat, fiber, and potassium and averaged more than 100 percent of the recommended intakes of vitamin C, folate, vitamin B6, calcium, and magnesium. While approximately half of all women achieved the recommended intakes of vitamins C and B6, less than one-third, including those born in Mexico, did so for vitamin A, vitamin E, folate, calcium, and magnesium on a given survey day. These percentages must be interpreted with caution, however, because single 24-hour recalls do not represent a person's usual intake. With multiple days of dietary data, the distribution of usual nutrient intake would narrow, and more people would probably achieve the recommended intakes (38). Nonetheless, other studies (39
, 40
) also have reported low percentages of Mexican-American women meeting the recommended intakes of folate and calcium. In light of the recent increase in the recommended amounts of these nutrients and vitamin E (34
, 35
), nutrition education emphasizing these nutrients may be especially important for all Mexican-American women, regardless of their country of birth or acculturation level.
An important finding was the higher percentages of US-born women and men who reported taking a vitamin or mineral supplement at least once in the previous month. Interestingly, similar numbers of US-born Mexican-American Spanish- or English-speaking women reported dietary supplement use. Although nutrient intakes from food sources may decline with increasing acculturation, absolute intakes of vitamins and minerals may improve with increased supplement use.
In our study, women and men born in Mexico, compared with those born in the United States, consumed more fruits, vegetables, and grains and legumes and had the highest intakes of traditional Mexican foods such as cornbread, tortillas, beans, and rice. Our findings agree in part with those of other studies (9, 11
, 37
, 41
) that also reported that more servings of traditional foods were eaten by less-acculturated compared with more-acculturated Hispanics. Otero-Sabogal et al. (41
) also found a higher fruit intake among less-acculturated Hispanics. Our finding of higher vegetable intakes among women and men born in Mexico was inconsistent with other studies that have shown vegetable intakes to be lower among less-acculturated Mexican Americans (9
, 37
, 41
). However, this difference may be explained by how vegetables were defined. For example, some studies excluded potatoes and corn; the FFQ we used included these foods as vegetables. Also, our FFQ had 12 questions about vegetables, while other questionnaires included as few as one question. Research has shown that the frequency of foods reported increases with the number of items asked on the FFQ (38
).
We also showed lower intakes of desserts and added fats among adults born in Mexico compared with US-born Mexican Americans, a finding that agrees with Schaffer et al. (9). However, other studies have reported higher rates of fat avoidance by Latinos as acculturation increases (42
, 43
). These discrepant findings are likely due to differences in the six-item scale used to determine fat avoidance compared with the NHANES III FFQ that asked about three types of added fats.
Overall, several factors may account for any discrepancies between our study and other studies of the dietary intakes of Mexican Americans, including temporal trends in food intakes, different methods of collecting dietary information, changes in nutrient and food databases, and samples from different regions of the country (38). Data from all studies were collected in the 1980s, and our study continued through 1994. Thus, the time frames for all studies were similar. However, the National Cholesterol Education Program was introduced in the late 1980s, and the mass media encouraged the general population to reduce their dietary fat and cholesterol intakes (44
). Many lower-fat foods also were introduced in the marketplace. Nonetheless, our results regarding dietary fat are consistent with those reported prior to introduction of the National Cholesterol Education Program. Most studies of Mexican Americans used similar methods to collect dietary data (i.e., 24-hour recalls to determine nutrient intakes and FFQs to determine food intakes), but the length of the FFQs (e.g., 22 items in the Hispanic Health and Nutrition Examination Survey vs. 62 items in NHANES III), the content of certain items on the FFQs (e.g., added fats), and the time frame (e.g., past month vs. past year) varied. Another likely explanation for any discrepancies is use of different nutrient and food databases to determine nutrient intakes. For example, prior to NHANES III, the US Department of Agriculture databases were more likely to include Americanized, commercially prepared Mexican foods rather than the recipes of foods prepared in Mexican-American homes (45
). Different databases also may partially explain conflicting results between regions of the country, despite control for SES (12
, 13
). Moreover, Mexican Americans living in different regions of the United States may have access to different foods, especially if the availability of foods changes with the seasons.
Limitations and strengths of our study
One limitation of our study is the cross-sectional design of NHANES III, which prevented us from drawing causal inferences. Dietary assessment tools also have inherent limitations (38). For example, a single 24-hour dietary recall is not representative of individual nutrient intakes because of day-to-day variation in food consumption, and the FFQ used in NHANES III is qualitative (i.e., it did not include portion sizes, which are required to quantify the number of servings of foods eaten). However, a single 24-hour recall is valid for measuring nutrient intakes of groups, and the FFQ may be useful for ranking persons in terms of the frequency of foods or food groups reported (38
). Moreover, inclusion of two dietary instruments enables a general comparison of results from each tool (e.g., intake of total fat from the 24-hour dietary recall and added fats from the FFQ). As mentioned previously, another limitation regarding dietary data is the accuracy of the nutrient and food databases used. However, substantial care was taken to include a wide variety of traditional Mexican foods and to ensure the accuracy of the nutrient contents of these foods in the NHANES III database (Catherine M. Loria, National Center for Health Statistics, personal communication, 1998).
A further limitation of NHANES III is the unavailability of in-depth data on some important variables. For example, our measure of acculturation was based on primary language spoken at home, which is a simple indicator of a very complex adaptation process involving attitudes, cognitive factors, and personality in addition to language (46). This definition may explain the inconsistent pattern of differences we found between Spanish-speaking and English-speaking US-born Mexican Americans. However, language use is a central part of the acculturation process and has been used previously as a proxy for acculturation (23
).
It is also possible that our results showing healthier nutrition profiles for persons born in Mexico may be explained by the "healthy migrant" effect, whereby persons who immigrate to the United States consume more nutritious diets than do persons who do not immigrate (47). Therefore, our dietary intakes may not be representative of all women and men born in Mexico.
These limitations are balanced by the strengths of NHANES III, which is one of the most extensive US surveys in existence and includes multiple dietary measures. NHANES III also oversampled Mexican-American women and men, thus providing sufficient numbers of participants in the three acculturation groups and sufficient numbers of women and men from both the lower and upper SES strata. Moreover, our analyses adjusted for education in addition to migration and acculturation status, strengthening our observations of differences in dietary intakes among Mexican Americans living in the United States.
Public health implications
The Hispanic population is anticipated to increase from 31.4 million in 2000 (11.4 percent of the US population) to 96.5 million in 2050 (24.5 percent of the US population) (48). Mexican Americans are projected to constitute the largest increase of all Hispanic groups. As future generations of Mexican Americans make the transition further away from their native culture, healthful diets should be encouraged to prevent an increased risk of heart disease and premature mortality.
Our findings of more healthful nutrition profiles among persons born in Mexico highlight the need to encourage all Mexican Americans to eat more foods such as whole grains, beans, and cereals as well as fruits, vegetables, and dairy foods that are low in fat and high in fiber, vitamins, and minerals. Nutrition education is needed for second-generation Mexican Americans as they become further removed from the heart-healthy traditions of their native country and enter a social milieu in which unhealthy foods are ubiquitous.
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ACKNOWLEDGMENTS |
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The authors thank Drs. David Ahn, Gladys Block, Rakale Collins, Cathy Cubbin, Christopher Gardner, Michaela Kiernan, Helena Kraemer, and Fran Thompson for their insightful comments on earlier drafts of this paper and Alana Koehler for her technical assistance.
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NOTES |
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REFERENCES |
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