Fast food consumption and its associations with obesity and hypertension among children: results from the baseline data of the Childhood Obesity Study in China Mega-cities

The prevalence of obesity and overweight has increased rapidly among Chinese adults and children over the past three decades [1–5]. In children, it increased from less than 3% in 1985 to about 20% in 2010 [4]. It has reached 42.6% in Chinese adults by 2010 [6]. It is much more prevalent in major cities, reaching about 50% in Beijing children in recent years. There are also indicators of worsening of other health problems like elevated blood pressure (BP) [7]. In a recent study based on data collected during 2004–2014, we reported adverse trends in ideal cardiovascular health indicators among Chinese children and adolescents [7]. The ideal levels of almost all the seven metrics, including smoking, diet, body mass index (BMI), and BP, suggested by the American Heart Association’s 2020 Strategic Goals, had decreased among Chinese Children [7]. According to a recent report, 20.2% of Chinese boys and 16.3% of girls had elevated BP; elevated BP was also common among obese children [8]. This is much higher than among American children [9]. The shifts in Chinese children’s food intake might have contributed to the increase in obesity and hypertension.

The fast food (FF) industry and people’s fast food consumption (FFC) have grown rapidly in China [10]. The number of McDonald’s alone rose from 1 to 1000 between 1990 and 2006 [10, 11]. At present, ‘Yum! China’ has approximately 4800 KFCs and 1300 Pizza Huts, with a plan to open around 20,000 restaurants in China [10]. FF is high in unhealthy fats, salt, and sugar, which contributes to obesity and elevated BP [11] and has been positively associated with the obesity epidemic due to its increasing availability, energy density, and large portions [12–14]. Some studies have reported that sodium intake was associated with elevated systolic blood pressure (SBP) and diastolic blood pressure (DBP) both among adults [15–20] and children [21–23].

In Western countries, although a positive association has been suggested between frequent FFC and weight gain in adults [24–26], there is limited and mixed evidence for children [27–32]. Some studies have shown a small association between FFC and increased BMI [12, 27–29], while others did not detect a significant association [30–32]. One multicenter, multi-country cross-sectional study of 199,135 adolescents aged 13–14 years, including adolescents from Mainland China and Taiwan, and 72,900 children aged 6–7 years, including children from Taiwan but without children from Mainland China, suggested that children’s BMI was higher for those who consumed FF more frequently, however, adolescents’ BMI was lower for those who consumed FF more frequently [13]. Two systematic reviews suggest the need for more studies using larger study samples and adjusting for confounding factors such as parental BMI [12, 13].

Some previous studies have examined the association between FFC and obesity in China, while most previous research has focused on Western FFC. Some reported a positive association [10, 33–37], while some did not [38, 39]. They are predominately cross-sectional studies and are based on local samples. Few have studied the predictors of FFC and the association between FFC and other health outcomes such as elevated BP.

To address these research gaps, this study aimed to: a) examine the current FFC (both Western FF and Chinese FF) patterns among school-age children in four mega-cities across China; b) explore factors being associated with FFC; and c) assess the association between FFC and selected health outcomes (i.e., obesity, central obesity, and elevated BP). We also examined gender differences in FFC and health outcomes among children, and how maternal factors may be associated with children’s FFC and having obesity and elevated BP.

Using data collected from four mega-cities across China, we have reported on FFC and its associated factors among elementary and middle school students. This is one of the first studies to examine the associations between FFC and obesity, central obesity, and hypertension among students in mega-cities across China. FFC is prevalent among children in mega-cities, and has been increasing steadily over the past decade. Chinese children in urban areas consumed FF much more frequently than those in rural areas. About 50% of our studied students reported having consumed Western FF (51.9%) and/or Chinese FF (43.6%) at least once per week over the past 3 months. The 9-province China Health and Nutrition Survey data reported that 18.5% (38.0% in urban vs. 11.0% in rural areas) of school children had consumed Western FF over the past 3 months in 2004 and 23.9% (43.3% in urban vs. 15.9% in rural) in 2009 [39].

Our study found that 11.1% of these students were obese, while 26.2% were overweight or obese. The prevalence was higher than the national average. Based on the 2010 Chinese National Surveys on Students’ Constitution and Health data, the national overweight/obesity prevalence was 22.6% in urban areas and 16.2% in rural areas [4].

The hypertension prevalence was 9.0% in these Chinese students, which is similar to that in American children but lower than Chinese national prevalence. According to a recent report, 20.2% of Chinese boys and 16.3% of girls had elevated BP [8]. The China Health and Nutrition Survey data reported that hypertension prevalence among children in 2009 was 16.2% in urban areas and 13.0% in rural areas [43]. Differences in BP measurements and the study populations could have contributed to these differences. The U.S. National Health and Nutrition Examination Survey data showed that mean BP and prevalence of elevated BP among U.S. children and adolescents had declined during 1999–2012, although the prevalence of obesity/overweight had increased. In 2009–2012, the prevalence of elevated BP and hypertension in U.S. children and adolescents were 9.6% and 1.6%, reduced by 2.8% and 1.3% from 1999 to 2002, respectively [9]. These declines among U.S. children and adolescents might be associated with decrease in some nutritional factors (e.g., daily intakes of energy, carbohydrate, total fat, and total saturated fatty acids), and increase in daily intake of total polyunsaturated fatty acids and dietary fiber [9]. However, Xi et al. reported that the mean BP and the prevalence of pre-hypertension and hypertension among Chinese children age 6–17 years increased significantly from 1993 to 2009, and the increases could be partially attributed to the increases in general and central obesity, salt intake and sedentary behavior, and decrease in physical activity [43]. More studies are warranted to examine the trend and risk factors for hypertension among children in China.

In China, over the past two decades, rapid economic development, global trade, and cultural exchange have meant that the FF industry and children’s FFC have been increasing rapidly [10]. However, we did not detect associations between FFC and obesity, central obesity, and hypertension. Inconsistent with results of the multicenter, multi-country cross-sectional study which showed FFC was positively associated with children’s BMI but negatively associated with adolescents’ BMI [13], our results found neither Western nor Chinese FFC was associated with child BMI (data were not shown). These may be due to the cross-sectional data, which cannot assess causality. Overweight children might have changed their dietary patterns, e.g., reduced FFC. This may distort or mask the associations between FFC and obesity.

Previously mixed results based on cross-sectional data have been reported on the association between FFC and obesity among Chinese children. A study among children in Beijing reported that children who consumed FF ≥ 3 times per week were 50% more likely to be obese (OR and 95% CI: 1.50 [1.12–2.02]) compared to those had indulged < 1 time per week [33]. Another study among middle and high school students from seven large cities in China reported a reverse association between Western FFC and overweight-adolescents who were overweight were more likely to consume FF less frequently (OR and 95% CI: 0.93 [0.87–0.99]) [44].

Other reasons for the mixed results being reported on the association between FFC and obesity may include that some studies only examined frequency of FFC and did not consider the quantity of FFC. The contribution of FFC to total energy intake varied considerably between populations. FFC played a much more dominant role in American children’s diet than for children’s diet in China. One study reported that FFC contributed to about 20% of American children’s total energy intake, but only < 0.1% for Chinese children [45]. Nevertheless, a growing body of research suggests FFC contributed to increased caloric intake and obesity risk [10, 12].

Of interest, we also found significant associations between maternal education and BMI and their children’s health outcomes. Higher maternal education and lower maternal BMI seem to be protective. Compared to children with mothers having college or above education level, those whose mothers had elementary school or below education were 49% more likely to consume Western FF. Children of mothers with lower education were 71% and 43% more likely to have obesity and central obesity, respectively. As mothers’ BMI increased, their children were more likely to have obesity, central obesity, and hypertension. This indicates mothers should be a key part of future childhood obesity prevention programs in China.

In this study, we defined Western FF as food sold in these fast food chains, e.g. KFC, McDonald’s, Pizza Hut, and defined food from non-westernized style quick service vendors, including food stalls, as Chinese FF. There may be some non-fried food (e.g., steamed buns and noodle soup) sold in food stalls. This would make our estimate more conservative. However, the components, nutrients, and health consequences of Western and Chinese FF may be different. More studies are needed to identify the differences between Western and Chinese FFC and their single and co-association with obesity, hypertension, and other health-related outcomes.

Our study has several main strengths. First, key outcome variables (i.e., height, weight, waist circumference, and BP) were objectively measured rather than self-reported. Second, some important confounders were controlled for in our models testing the associations between FFC and health outcomes, including maternal BMI and maternal education. Some limitations should be considered when interpreting our results. First, the definition of FFC was determined by eating in Western-style FF restaurants or eating a meal or snack in a food stall or in a non-westernized FF restaurant. In this case, FF bought from supermarket and ate at home may have not been considered. Second, we used modified food frequency questionnaires (FFQ) to estimate FFC instead of using 24 dietary recalls. There were both pros and cons of using these methods. Given the large sample in our study, we chose to use FFQ. So, we could not obtain information on the quantity of FFC, total daily energy intake, and FFC’s contribution to total daily energy intake among the children. It may affect the assessment of the relationship between FFC and health outcomes. Third, we could not make causal inference due to cross-sectional data structure. Fourth, study participants were 7–16 years old students from four mega-cities across China, which are more developed than other small cities and rural areas of China. Thus, our results could not represent children and adolescents living in small cities or rural areas of China.

Therefore, more studies, especially longitudinal studies based on large national representative samples with exact measures of quantity of FFC intake and its contribution to total daily energy intake, are needed to detect the association between FFC and health outcomes. We are collecting follow-up data which would allow us to conduct longitudinal studies in the future.

The prevalence of FFC, obesity, and hypertension is high among children in mega-cities in China. The obesity prevalence was much higher in boys, and the FFC and hypertension prevalence was higher in older children. Maternal factors affect child FFC and health outcomes. Children of mothers with low education were more likely to have FFC, and with the increase in maternal BMI, children were more likely to be obese and have hypertension. Associations between FFC and obesity, central obesity, and hypertension were not detected. More studies are warranted. To fight the epidemic of obesity, hypertension, and increasing FFC among children, national and regional programs and policies are needed to create a healthy food environment and promote the development of healthy lifestyles in young people. School-based programs are also needed to provide effective health education and health promotion for children. More attention should be given to boys, and health education should begin at young ages and cover parents.