Introduction

The recent three decades saw a growing global obesity epidemic; and overweight and obesity rates among children have increased in many countries including China[1–3]. In the U.S., the prevalence of childhood overweight and obesity has tripled since the 1970s[4]. In China, overweight and obesity prevalence has increased rapidly in children, from less than 3% overall in 1985 to approximately 10% in girls and 20% in boys in 2010, and the overall rate in major cities like Beijing is over 20%[3,5].

There has been a strong interest in developing effective childhood obesity prevention programs[6]. Along with the increasing obesity prevalence, research suggests that rapid economic development, urbanization, globalization, and changes in government policies followed by China’s entry of World Trade Organization (WTO) have led to emerging Western fast food outlets and dietary shifts among the Chinese population[7,8], which may have fueled the growing obesity epidemic. For example, since the first American fast food chain, Kentucky Fried Chicken (KFC), opened its first restaurant in China in 1987, the number of KFC restaurants has increased to over 4,200 in more than 800 cities and towns by 2012[9]. McDonald’s added 200 restaurant in 2011, and grew to over 2,000 restaurants within three decades in China[10]. In 2002, the fast food industry yielded 200 billion Chinese Yuan annual sales (approximately US$24 billion), accounting for 2/5 of China’s food and beverage sales[11].

The relationship between Western fast food consumption (FFC) and weight status remains mixed in the existing literature. Some research suggests a positive association while others do not [5,12]. Moreover, only a few cohort studies have tested the influence of FFC on obesity [13,14]. Very limited longitudinal studies have been conducted to examine the effect of FFC on weight status in children, and no study has been conducted in Chinese children[12].

This study examined the changes over time in FFC and tested the association between FFC and obesity (including overweight) among children in China using nationwide longitudinal data. We hypothesized that FFC had increased over time in China and FFC increased obesity risk in children.

Materials and Methods

Study design

We conducted both cross-sectional and longitudinal analyses using longitudinal survey data collected in the 2004 and 2009 China Health and Nutrition Survey (CHNS), which covered nine provinces throughout China[15]. Fig 1 shows the map of the CHNS coverage for these waves.

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Fig 1. Map of the China Health and Nutrition Survey (CHNS) coverage 2004–2009.

https://doi.org/10.1371/journal.pone.0151141.g001

CHNS is a large-scale, household-based open cohort which includes about 4,400 households and 26,000 individuals in the nine provinces, namely Heilongjiang, Liaoning, Shandong, Henan, Jiangsu, Hubei, Hunan, Guizhou, and Guangxi. CHNS used a multi-stage, random cluster sampling scheme to collect nationally representative data that covered key public health risk factors and health outcomes, demographic, social and economic factors at the individual, household and community levels[16]. At the individual level, detailed health-related data were measured, including dietary intake, physical activity, smoking and drinking behaviors, anthropometrics, blood pressure and limited clinical data[16].

Results

Study Sample Characteristics

Table 1 shows the subjects’ socio-demographic characteristics. On average, children in wave 2009 were slightly younger than those in 2004, had higher family income, with more residing in South China and fewer in the Northeast region, consumed fewer daily calories, had lower physical activity levels, and had higher average BMI z-scores. Other characteristics were comparable in 2004 and 2009.

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Table 1. Socio-demographic characteristics of children aged 6–17 years in nine provinces in China: China Health and Nutrition Survey 2004–2009 (cross-sectional analysis).

https://doi.org/10.1371/journal.pone.0151141.t001

Trends in Fast Food Consumption

Table 2 presents the time trends in the proportion of fast food consumers by socio-demographics, lifestyles and weight status for the same cohort aged 6–12.99 years in 2004 (thus aged 11–17.99 years in 2009). The proportion of fast food consumers rose from 18.5% in 2004 to 23.9% in 2009 (P<0.001). The increase was greater in boys (16.3% to 21.1%, P<0.001) than in girls (23.6% to 24.4%, P<0.001). The figure in minority ethnic group almost tripled (P<0.001) over time, far faster than that in Han people.

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Table 2. Longitudinal analysis: Trends in the percentage (%) of Western fast food consumers among Chinese school-age children followed up from 2004 to 2009 (the same cohort, n = 376), by socio-demographics, lifestyles and weight status: China Health and Nutrition Survey 2004–2009^†.

https://doi.org/10.1371/journal.pone.0151141.t002

The rise in the percentage of fast food consumers was most pronounced in the low- and median- income groups (10.3% to 19.2% in low-income households; 11.2% to 18.5% in medium- income households, both P<0.001). It decreased significantly in the high-income group (36.2% to 35.1%, P<00.01).

The same trends existed among the urban and rural residents. The percentage increased dramatically in both urban (38.0% to 43.3%, P<0.05) and rural residents (11.0% to 15.9%, P<0.001).

While the percentage consumed increased dramatically in the Northeast (17.5% to 29.0%, P<0.001), South (5.7% to 13.4%, P<0.001) and Southwest regions (5.8% to 15.7%, P<0.001), it decreased slightly in the remaining regions.

In terms of dietary intakes, the percentage of fast food consumers increased significantly (20% to 25.2%, P<0.001) among those who consumed 1,200 kcal or more calories per day. The percentage of fast food consumers increased in all fat and carbohydrate intake subgroups.

Compared to 2004, more children with a low physical activity level (MET in kcal/(kg*h) ≤5,000) consumed fast food in 2009 (16.9% in 2004 to 23.7% in 2009, P<0.001), while fewer children with a high physical activity level (MET in kcal/(kg*h) >5,000) consumed fast food (26.2% in 2004 to 24.7% in 2009, P<0.001). Among children with different weight status, more underweight or normal weight children consumed fast food in 2009 (19.7% in 2004 to 25.1% in 2009, P<0.001), compared to to those who were overweight (22.9% in 2004 to 18.8% in 2009, P<0.001),

Table 3 shows the trends in the percentage of fast food consumers by socio-demographics, lifestyles and weight status characteristics for participants of the same-age in 2004 vs. those in 2009, i.e., to examine the time trends controlling for age. From 2004 to 2009, more adolescents aged 13–17 reported consuming fast food, while it did not change much in children aged 6–10. For children aged 13–17, there was a dramatic increase (17.9% to 26.3%, P<0.01). Among children aged 6–10, it did not change much, but it more than tripled among ethnic minorities (5.2% to 16.9%, P<0.05), while it decreased in East China (where the proportion was high in 2004) over time (43.3% to 32.1%, P<0.01).

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Table 3. Time trends in the percentage (%) of Western fast food consumers among Chinese children of the same age between 2004 and 2009, by age group (those aged 6–10 vs 13–17 years old), socio-demographics, lifestyles and weight status: China Health and Nutrition Survey.

https://doi.org/10.1371/journal.pone.0151141.t003

FFC rates were significantly higher in the medium-income group (13.7% to 22.2%, P<0.05), among rural residents (10.3% to 20.6%, P<0.001), among those who consumed 12,00 kcal or more per day (18.3% to 26.7%, P<0.01), among those who consumed more fat (23.2% to 36.8%, P<0.05), and among those who were under or normal weight (17.4% to 26.2%, P<0.001). The consumption rate was higher in ball carbohydrate intake and physical activity level subgroups. The consumption rate was mostly stable in other groups.

Association between Fast Food Consumption and Children’s Weight Status

Using linear and logistic regression analyses, we assessed cross-sectional associations between Chinese children’s FFC and BMI z-scores and weight status in both wave 2004 and 2009, respectively, with stratification by gender (Table 4). After controlling for potential confounders including age, ethnicity, household income, urbanicity, geographical region and physical activity levels, FFC was positively associated with BMI z-score (β = 0.13, 95% CI: -0.16, 0.42, β = 0.41, 95% CI: 0.04, 0.78 for boys in 2004 and 2009 respectively) and weight status (OR = 1.62, 95% CI: 0.52, 5.12, OR = 2.79, 95% CI: 0.87, 8.97 for boys in 2004 and 2009 respectively) in wave 2004, while it was not significant in 2009. However, most of the associations were not significant, except for that of FFC and BMI z-score among girls.

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Table 4. Linear and logistic regression analysis for cross-sectional and longitudinal associations between Chinese children’s Western fast food consumption and their BMI z-scores and weight status: China Health and Nutrition Survey 2004–2009.

https://doi.org/10.1371/journal.pone.0151141.t004

Further linear and logistic regression analysis (Table 4) examined the longitudinal associations between FFC and BMI z-score and weight status, and stratified by gender. Our estimates suggest that FFC was associated with 0.02 (95% CI: -0.71, 0.75) higher BMI-z in boys, but 0.14 (95%CI: -1.03, 0.75) lower BMI-z in girls. However, none was statistically significant (p>0.05). Sensitivity analyses were conducted before FFC was imputed, and showed similar results (not shown here).

Discussion

Our analysis of the nationwide survey data shows that FFC (excluding Chinese fast food) increased significantly among Chinese school-age children during 2004–2009, and the increase was especially rapid among some groups such as older children, boys, those from low- and medium-income families, and those from rural areas and East China, compared to their counterparts. During this period, FFC decreased in children who were from high-income families and those who were overweight. In almost all socio-demographic subgroups, as children aged, more respondents reported having consumed fast food in the past three months. This finding was likely to be fueled by the increased accessibility of Western fast food restaurants and children’s increased pocket money and independence. The trend was different by age group. FFC rate in children was relatively stable, while it increased rapidly in adolescents, from 17.9% to 26.3%. For adolescents, the increasing trend was prominent in boys, of Han ethnicity, from medium-income families, of rural residents, from East China, of under/normal weight, or those with a diet high in calories or fat. These findings are likely due to their increased independence and peer influence.

The Western fast food industry has been growing rapidly in China. Compared to a decade ago, nowadays children have better access to fast food and the food has become more affordable. Moreover, FFC is viewed favorably among children. A cross-cultural study on brand identity reported that Chinese children had more favorable impressions of KFC than did their US counterparts [21]. Despite these changes in the food environment in China, our findings indicate some large spatial-temporal disparities and time trends in FFC in adolescents between urban and rural regions: urban adolescents had more FFC. However, during 2004–2009, FFC increased in rural areas, but decreased in urban areas. Such spatial-temporal differential patterns mirror the inequalities of regional economic development and reflect the nonlinear effect of income rise on food-away-from-home (FAFH) consumption. It is known that an increase in income generates a greater increase in FAFH expenditure in high-income households than in low-income households in China[22]. On one hand, as an important component of FAFH, FFC increased dramatically in rural areas with an increase in rural household income. On the other hand, the effect of increasing household income in urban areas on FAFH was more pronounced for other foods. In high-income urban households, more awareness of health, media influence, and increased demand for high quality food in recent years may have resulted in a decrease in FFC, as FFC may be increasingly viewed as unhealthy for children. We have not observed such pattern in rural areas yet, likely because of nonlinear income effects at different threshold levels. Further research is warranted to explain what we observed.

By separating the age and period effects, we found different patterns. In general, as age increased, more children had consumed Western fast food, while the consumption prevalence in young children did not change much. This finding is likely because adolescents who had entered middle and high schools had more autonomy and pocket money, and were more likely to be under peer influence than younger kids [23,24]. Therefore, older children had more freedom and opportunities to consume Western fast food.

Interestingly, the FFC rate decreased in the children from high-income families, but those from low- and medium-income families increased their FFC. This result is consistent with the shifted nutrition transition and findings that the burden of obesity and metabolic risk has started to move from the better-off to the poorer population groups in some developing countries [25].

Although FFC generally increased, western FFC did not appear to be a large contributor of childhood obesity in China. We did not find a meaningful association between western FFC and child weight status using the CHNS data. Another study reported that less than 1% of Chinese children’s total calorie intake was obtained from fast food in 2000, while the proportion was 14.8% for children in the United States [26,27]. Other factors have contributed to childhood obesity in China, such as increased family income and increased consumption of animal-source food [28]. Also, using the CHNS data, Du et al. found that the density of fast food restaurants in neighborhood was not associated with BMI in men in rural China, while an increase of one fast food restaurant was associated with lower BMI (by 0.02) in rural women [29]. The CHNS data also show that overweight and obesity was not associated with fast food preference in adults, and food environment might play a smaller role than nutritional knowledge in influencing consumers’ consumption choices [30]. These findings for adults may indicate the complex relationship between FFC and weight outcomes in Chinese children as well.

Some empirical and review studies have examined the associations between FFC, increased fat and calorie intakes and childhood obesity[12,31]. However, most of these findings were based on studies conducted in high-income countries such as the United States. To our knowledge, thus far, Rosenheck’s (2008) review is the most comprehensive to date in its review of 16 studies (6 cross sectional-, 7 prospective cohort-, 3 experimental studies). It concluded that the association between FFC and weight gain was not clear, but sufficient evidence exists for public health recommendations to limit FFC and facilitate healthier menu selection. Of the 7 prospective cohort studies, 4 were conducted among children and adolescents, 6 found a positive association between more frequent FFC and an increase in total caloric intake or BMI. All 3 studies conducted among young adults reported an association between FFC and increased BMI. Period effect is a potential cause for our mixed findings. We found that the percentage of fast food consumers decreased from 2004 to 2009 among children from high- income families, but it increased in both low- and medium- income families. Over time with increased family income, more and more Chinese families can afford eating fast food on a regular basis. More future research is needed to study the impact of FFC on public health in China.

Our study helps fill two main gaps in the literature: only a small number of studies have tested the association between FFC and overweight/obese in developing countries, and very few previous studies have used longitudinal data. Two large cross-sectional studies have examined the association in China, but provided conflicting findings. Our previous cross-sectional study among 21,198 children in Beijing reported a positive association between FFC and overweight/obese[5], but another study among 9,023 adolescents from seven large cities in China reported a negative association[32].

Consistent with findings from a recent US study (29), our present study did not detect a significant association between FFC and childhood obesity. The lack of an association could be because FFC only accounts for a small proportion of Chinese children’s total energy intake, our sample size is relatively small, and there is measurement error in assessing FFC. One of our recent studies shows that the density of neighborhood restaurants was associated with BMI in rural Chinese adults[29]. Nevertheless, FFC may affect overweight/obesity indirectly. For example, FFC may have promoted western food culture among Chinese children, which may influence their other food intake and cause a shift to high energy density food and drinks at home or away from home.

The main strengths of our study include longitudinal analysis and stratified analysis to examine the time trends in FFC and the association between FFC and obesity in Chinese children. The study also has several limitations. First, only 376 children had complete follow-up data. The low follow-up rate was mainly because children were not at home during the follow-up data collection and some families had moved out of the previous community. Second, the definition of fast food was not clearly specified in the survey questionnaire. The survey question asked about the number of times children visited fast food restaurants like McDonald’s. In this case, other Western fast food restaurants may have not been taken into account.

In conclusion, more Chinese children have consumed Western fast food over time. The increase is dramatic and is more rapid in some groups such as among adolescents (vs. younger children), boys, of non-Han ethnicity, those from low- and medium-income families, and those from rural areas or East China. FFC has been linked with adverse dietary quality and health conditions. Efforts are needed to study the impact of FFC on health outcomes, as well as the methods to promote healthy eating among young people in China.

Acknowledgments

We thank Dr. Huijun Wang from the Chinese Center for Disease Prevention and Control and Dr. Shufa Du from University of North Carolina at Chapel Hill for their assistance in data management.