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Department of Culinary Science, Honam University, Gwangju, Korea (E.J.Y.)
Department of Food Science and Human Nutrition, Michigan State University, East Lansing, Michigan (J.M.K., W.O.S.)
Address reprint requests to: Won O. Song, PhD, MPH, RD, Professor of Human Nutrition, and Acting Dean, 7 Human Ecology Bldg., Michigan State University, East Lansing, MI 48824-1224. E-mail: song{at}msu.edu
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ABSTRACT |
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Methods: A cross-sectional study was conducted with KAs residing in Michigan using a mail survey. Of 1,860 questionnaires mailed to KAs in Michigan, 637 (34%) responded and 497 first-generation KAs (263 men, 234 women, aged 30–87 y) were included in the final analyses. A factor analysis was used to identify dietary patterns from a 93-item food frequency questionnaire developed for KAs (KFFQ).
Results: Major dietary patterns of KAs were labeled "vegetable/fruit," and "traditional Korean" in both men and women and "acculturated American" in men and "traditional American" in women. The "traditional Korean" dietary pattern was negatively associated with length of residence in the U.S. for both men and women (p < 0.01). The other major dietary patterns were not associated with other sociodemographic variables examined in men; however, the "vegetable/fruit" dietary pattern was positively associated with length of residence in the U.S. (p < 0.05) and education level (p < 0.05) in women.
Conclusions: Dietary pattern analysis can be used to understand dietary behaviors regarding health risks of ethnically different immigrants including KAs.
Key words: Korean American, dietary pattern, food frequency questionnaire (FFQ), factor analysis, length of residence, health risk
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INTRODUCTION |
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Research regarding KAs’ dietary intake has been limited to studies on specific dietary practices, single or specified nutrient intakes, or food intake [6–8]. Although these approaches have been valuable, they provide little information regarding the total diet, which includes a variety of foods with complex combinations of nutrients that are likely to be interactive or synergistic [9]. Since dietary intake is such a complex exposure variable, we need to develop and refine methods of assessing dietary intake that focus on the total diet and not just individual dietary components. Thus, the study of dietary patterns using multivariate data analysis techniques (e.g. factor analysis) is burgeoning in nutrition research. Assessment of the total diet by using dietary pattern analysis takes into account all nutrient interactions and allows us to capture diet-disease or diet-biomarker relationships without knowing the exact nutrient or food component involved [10]. The methodology for defining dietary patterns is relatively new and is still in the process of development [11]. Little has been reported on the methods to examine dietary patterns of immigrants who have unique or modified ethnic-specific dietary patterns.
Dietary patterns are likely to vary according to sex, socioeconomic status, and ethnicity [12]. In a large study of U.S. men, those subjects who had higher scores for a "Western" dietary pattern were more likely to have lower levels of income and education [12]. Also, in other studies with U.S. subjects, dietary patterns differed by gender or age [13,14]. Dietary behaviors of immigrants have been related to acculturation status such as current age, years in the U.S., total years of education, percentage of lifetime in the U.S., and age entering the U.S. [15].
Because of the associations between dietary intake and sociodemographic and acculturation status, it may be useful to test dietary pattern scores derived from multivariate data analysis techniques (e.g. factor analysis) in a linear regression model in which sociodemographic and acculturation status variables are entered as the predictors (i.e. independent variables). Identifying the appropriate methods to define dietary patterns and examining other variables related to dietary patterns of KAs will provide valuable information regarding the total diet and a practical way for studying dietary patterns in relation to health outcomes of ethnically different immigrants as well as KAs.
Therefore, the purposes of this study were 1) to test a method for defining dietary patterns using dietary intake data of KAs and 2) to examine the relationship of dietary patterns to sociodemographic characteristics.
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METHODS |
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All individuals listed in the Michigan KA Telephone Directory (n = 2,625, published by Korean American Community of Metro Detroit in 1998) received a post-card requesting their participation, followed by the survey questionnaire in both Korean and English language formats. Among them, 765 had invalid addresses and their surveys were returned. A total of 1,860 KAs were included in the survey. Of those, 637 (34.3%) responses were returned with completed consent forms. The subjects excluded from further analyses were those with invalid and incomplete responses, who had missing values on the food frequency questionnaire (FFQ) or who had consumed fewer than 20 food items on the FFQ (n = 59), subjects with missing data for age or residency (n = 2), subjects who were pregnant (n = 7), subjects who were less than 30 years of age (n = 69), or subjects who were not first generation Korean American (n = 1). The number of subjects included in the final data analysis was 497 (263 men, 234 women) first-generation KAs, aged 30–87 years old. The study was approved by the University Committee on Research Involving Human Subjects (UCRIHS) of Michigan State University.
Instrument
The questionnaire included demographics (age, gender, length of residence in the U.S., and education level) and a 93-item food frequency form. The semi-quantitative 93-item food frequency questionnaire for KAs (KFFQ) was adapted from the Health Habits and History Questionnaire (NHIS, 1987 [16,17]) and the third National Health and Nutrition Examination Survey (NHANES III, 1988–94 [18]). The KFFQ was modified after a validation study by the first author of this paper in Korea [19], which was supplemented with Korean National Food Record data [20] and contained food items available at general grocery and Korean grocery stores in Michigan. It consisted of food items in 10 frequency of consumption categories (
3 times/d, 2 times/d, 1 time/d, 5–6 times/wk, 3–4 times/wk, 2 times/wk, 1 time/wk, 2–3 times/mo, 1 time/mo, and never/rarely) and portion sizes in three levels (small, medium, and large) as guided by the Korean Nutrition Association [21] and U.S. Department of Agriculture serving sizes [22], and referenced foods eaten in the past month.
Dietary Assessment and Food Groupings
Usual food intake to establish dietary patterns was estimated using the frequency of consumption per day multiplied by the portion size of each food item of the KFFQ. Ninety-three food items in the KFFQ were collapsed into 49 food groups based on the nutrient profiles of each food item [18,23] (Table 1).
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In determining the number of factors to retain, a step-wise process was utilized. Using eigenvalues over 1.25 as the criteria for retaining factors resulted in 10 factors for both men and women, respectively. With the additional criteria of examining the Scree plot and the interpretability of the factors [25], three factors for both men and women were considered as major dietary patterns of KAs and were labeled on the basis of our interpretation of the data (i.e., "vegetable/fruit," "traditional Korean," "acculturated American," or "traditional American"), which then were used in further analyses.
A factor score was created for each individual based on daily intake (the number of servings/food group/day) of 49 food groups. Each individual has a factor score for each factor that emerged from the data (e.g., "vegetable/fruit," "traditional Korean," "acculturated Western," or "traditional American"). Labeling of dietary patterns is a subjective process and was based on our interpretation of the foods with high factor loadings on each dietary pattern. We included only foods that were positively associated with a factor loading 0.3 for each factor in Table 2 for simplicity. We also included foods that were negatively associated (<–0.2) to incorporate the valuable information concerning infrequently consumed foods within each factor [26].
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RESULTS |
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Table 2 includes three major dietary factors of KAs that are labeled as "vegetable/fruit" and "traditional Korean" for all subjects, and "acculturated American" for men and "traditional American" for women. Even though the major dietary patterns between men and women were similar, the foods/food groups that characterized the dietary patterns were not the same. In men, "vegetable/fruit" was characterized by high intakes (i.e. high positive factor loadings) of vegetables, fruit, seaweed, and tomatoes; "traditional Korean" was characterized by high intakes of traditional Korean dishes such as soybean paste stew, anchovy, Korean style of grains, tofu, vegetables, kimchi, salted/fermented fish, seaweed, Korean style of soup, red meat, other seafood (shrimp, squid, clams, oyster, etc), and fish, with low intakes (i.e. negative factor loadings) of bread, and "acculturated American" was characterized by high intakes of poultry, American style of soup, potatoes, eggs, tomatoes, tofu, and vegetables, and low intakes of Korean style of grains. In women, "vegetable/fruit" was characterized by high intakes of vegetables, tomatoes, fruit, seaweed, nuts, and potatoes; "traditional American" was characterized by high intakes of butter, salad dressing, processed meat, margarine, bread, high-fat dairy products, red meat, potatoes, and eggs; and "traditional Korean" was characterized by high intakes of tofu, soybean paste stew, Korean style of grains, kimchi, eggs, vegetables, nuts, and seaweed. In men, the three factors accounted for 29.5% of the total between-person variance in dietary patterns (i.e. variance explained), and in women the three factors accounted for 27.4% of the total variance.
In linear regression analyses, where the factor score from each major dietary pattern was modeled as a continuous variable, we found that the "traditional Korean" dietary pattern in men was negatively associated with both length of residence in the U.S. and education level (Table 3). However, the "vegetable/fruit" and the "acculturated American" dietary patterns were not related to length of residence in the U.S., age, or education level in men. In women, the "traditional Korean" dietary pattern was negatively associated with length of residence in the U.S., while the "vegetable/fruit" dietary pattern was positively associated with length of residence in the U.S. and educational level, and the "traditional American" dietary pattern was negatively associated with length of residence in the U.S.
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DISCUSSION |
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Dietary pattern analysis considers overall diet rather than individual nutrients or foods. The analysis of dietary patterns has advantages over nutrient-based or food/food group-based dietary assessment approaches because it examines all foods consumed concurrently; the aggregation of these foods into dietary patterns is based on relationships among actual reported consumption patterns. Thus, the collinearity often seen between nutrients and/or foods in traditional dietary assessment approaches can be used to statistical advantage with the factor analysis technique because dietary patterns are characterized on the basis of eating behaviors including all nutrients and foods consumed in the entire diet.
Most previous studies identified more than two dietary patterns, reflecting cultural differences in some instances [27,28]. We defined each of three major dietary patterns for both KA men and women, respectively, and small gender differences were seen in the dietary patterns extracted from the data: "vegetable/fruit," "traditional Korean," and "acculturated American" in men, and "vegetable/fruit," "traditional American," and "traditional Korean" in women. Although each of the three dietary patterns for men and women, respectively, were statistically independent through the orthogonal rotation procedure, it is possible for one individual to have high or low scores on all three patterns at the same time [11]. Furthermore, eggs had high loadings on both the "traditional American" and the "traditional Korean" dietary patterns in women.
The "traditional Korean" dietary pattern in men was negatively associated with length of residence in the U.S. and education level, however, the "vegetable/fruit" and the "acculturated American" dietary patterns were not related to the length of residence in the U.S., age, or education level in men. Other factors such as combinations of sociodemographic characteristics, social activities or contact with people from different cultures and/or health behaviors may affect the dietary patterns in men. In women, the "vegetable/fruit" dietary pattern was positively associated with the length of residence in the U.S. and education level, while the "traditional Korean" and the "traditional American" dietary patterns were negatively associated with length of residence in the U.S. Randall et al. [26] reported that dietary patterns among women appeared to be influenced by differences in income levels. Kerver et al. [29] reported that vegetable-rich dietary patterns were associated with being female and having higher socioeconomic status. The dietary patterns may differ in the costs of foods included [26]. In the present study, women consuming the "traditional American" dietary pattern had high intakes of foods/food groups that were similar to the "Western" dietary pattern described elsewhere [29], which was characterized by a high intake of red meat, processed meat, potatoes, eggs, high-fat dairy products, sweet, and refined grains. Although we identified a meaningful "traditional American" dietary pattern for KA women, additional research is needed in order to determine whether individual sociodemographic characteristics or a combination of these are confounding estimates of dietary patterns of KAs. Our results indicate that KAs who had lived in the U.S. longer, consumed less traditional Korean food. However, the "vegetable/fruit" dietary pattern, as the primary dietary pattern for both men and women, was positively associated with length of residence in the U.S. in women, but not in men. Further research is needed to evaluate the effects of combinations of socidemographic or lifestyle characteristics on dietary patterns of KAs. Dietary patterns may either be independent from, or interact with, other variables including other sociodemographic and lifestyle characteristics. The relationship of dietary patterns to sociodemographic and lifestyle characteristics supports the theory that food choices are a part of a larger pattern of health-related characteristics and behaviors [30]. Further research is warranted in exploring the possibility that other sociodemographic variables and lifestyle characteristics affect dietary patterns.
Most immigrant studies of dietary intake report changes in food consumption patterns that mirror a Western-style diet after immigration, typically consisting of higher meat intake and lower vegetable intake. Many Japanese migrating to Hawaii and the continental U.S. have adopted Western-style diets [2,4,6]. KAs’ dietary patterns are likely to continuously change with increased acculturation [8]. However, the timing and degree of transition to the consumption of a more Western-style diet may vary by length of residence in the U.S. and other factors.
KAs who have been exposed to a "Western" lifestyle in the U.S. may change their dietary patterns, but two of the major dietary patterns (the "vegetable/fruit" and the "traditional Korean") of KAs for both men and women were more similar to that of a typical Korean diet than that of a typical American diet in spite of the fact that the "traditional Korean" dietary pattern was negatively associated with length of residence in the U.S. Kim et al. [6] reported that KAs increased their consumption of beef, dairy products, coffee, soda, and bread, and decreased their consumption of fish and rice. However, KAs in their study continued to consume diets more consistent with the traditional Korean diet rather than an American diet. Lee et al. [8] reported that dietary quality did not vary by acculturation status despite significant differences in dietary practices. Gordon et al. [7] also reported that KAs had longstanding and unchanged dietary habits and health beliefs. KAs may have a dietary pattern retaining some traditional Korean dietary practices while not completely adopting a traditional American dietary pattern.
In addition, dietary patterns of KAs or Asian immigrants appear to be influenced by meal type. Dinner remained the most traditional Korean meal, however, breakfast, lunch, and snack items were replaced by foods more commonly consumed by Americans [31]. In addition to describing dietary patterns by food intake only, research on dietary behaviors such as meal and snack type may be indicated. The relation of the Western-type dietary patterns ("traditional American" or "acculturated American") to meal-type variables along with sociodemographic and lifestyle characteristics should be determined in further research.
The use of factor analysis to define dietary patterns has been criticized for its subjective nature, including the consolidation of food items into food groups, the number of factors to extract, the methods of rotation, and the labeling of the components [11], and there is concern that results cannot be replicated across populations or even within the same population [32]. Three major dietary patterns in our results accounted for 29.5% of the total variance for men and 27.4% of the total variance for women. Thus, additional analyses on the minor dietary patterns may demonstrate additional associations between dietary patterns and socidemographic characteristics. In addition, the present study was based on a convenience sample of KAs residing in Michigan, most of whom had higher education. Since the subjects in the present study had a higher education level than the average reported for KAs by the NHIS, 1992–1994 [33] and multiple other studies [6,34,35], different dietary patterns of KAs may be found in other socioeconomic strata or other regions of the U.S.
Dietary pattern analysis using factor analysis to explore variables related to dietary patterns can be a useful approach to studying immigrants’ health outcomes. This type of research will provide important clues to identifying relationships between the changes in dietary patterns and health risks of immigrants who may change their lifestyle after immigration.
Received May 7, 2004. Accepted November 24, 2004.
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