Introduction

dolescence is referred to the age group of 10-19 years, and it is one of the most important periods of human development, since physical, psychological and social maturity happens in this period [1, 2]. Adolescents are at risk of many health-threatening behaviors, such as excess food intake and decrease in physical activity, which could be a threat to their future health [3]. Nutrition as an essential factor for growth and reproduction [4], plays a key role in children’s and adolescents’ health and directly affects their physical, mental, and cognitive development [5-7].

Nutritional issues in adolescents are mainly characterized by increased need for energy and nutrient intake and the changes in eating habits, which could induce different types of nutrition-related disorders in adulthood [8]. The unhealthy eating habits such as skipping breakfast, low intake of fruits, and high consumption of fast food/junk food are common in adolescents. These habits were strongly influenced by family members, peers and social media [9, 10]. Junk food and fast food are all definitions that have been used to describe the quick, unhealthy, hunger satisfying foods, which are easy to make and easy to consume. Junk foods are high in sugar or salt and calories and often poor in minerals, vitamins and fibers which can increase the incidence of diseases such as obesity, diabetes, cardiovascular diseases, and hypertension in adulthood [11-13].

Delicious taste and attractive food advertisement play an important role in attracting adolescents towards consuming junk food [14-16]. Advertising is one of the most tangible and crucial components of marketing process [17]. Advertisements influence the audience’s mind through media such as TV, radio, Internet, billboards, newspapers and magazines. These communication tools for transferring advertising messages can have a major role in the effectiveness of an advertisement [18]. Advertising affects food preferences, food consumption behavior and sales of a brands’ products [19].

There is strong evidences that food advertising influences children’s food preference, purchase and consumption [6, 20]. Each child in the United States on average watches 13 food advertisement on TV daily, and 30% of all TV advertisementviewed by children and adolescents [21]. It was estimated that the children view more than 40,000 TV food advertisement per year, 98% of which are about the foods containing high fat, sodium, and sugar levels [22, 23]. Food industries use the techniques such as animation, visual effects, story-telling, gift advertising, and music for more influence on children and adolescents [24]. TV is an integral part of children’s life in the world [25] andamong the various methods of advertising, TV advertisement has been recognized as the most effective method [26].

Excessive exposure to food advertisementgiven by media increases the probability of junk food consumption and subsequently chronic diseases in adulthood [27]. Also it increases the tendency to consume foods with high fat, sugar and salt levels especially in children and adolescents who spend more time watching TV [28]. On the other hand, the media including TV play an important role in formation of beliefs, behaviors, emotions, social personality, and social relations [29] as well as eating behaviors [30]. Obviously,it is necessary to improve nutritional behaviors and habits of adolescents [31]. Considering insufficient evidences and the negative consequences of junk food consumption [32], this study aimed to examine the relationship of junk food consumption with exposure to food advertisements in high school students.

Materials and Methods

This is an analytical study with cross-sectional design conducted in 2016. The study population consisted of all public high school students from two educational districts of Rasht city in Iran including 14 girls’ schools and 8 boys’ schools in the first educational district, and 12 girls’ schools and 11 boys’ schools in the second educational district (n=13654). The samples were selected by using cluster random sampling method where each classroom was considered as a cluster. The sample size was calculated 336 based on the study of Dehdari et al. [12] who reported R2=0.30 for the correlation between junk food consumption and behavioral intention, and considering 95% confidence leveland P=0.05.

Given the average number of 30 students per each classroom, 12 classrooms (4 from each grade) were selected randomly. One boys’ school and one girls’ school were selected randomly from both educational districts. Then,from these four selected schools, one classroom was selected randomly from each grade (a total of 3 classroomsfrom each school). Finally, 342 questionnaires were distributed among subjects. Only one male student refused to complete the questionnaire. Thus, data from 341 completed questionnaires were collected. Inclusion criteria were: studying in the 10th, 11th and 12th grades and having no any specific illnesses that may influence their diet based on a self report.

The self report Questionnaire designed by the researcher which had two parts adapted from similar studies. The first part records demographic characteristics of students, and the second part assess the source and frequency of exposure to fast food/junk food advertisement and the frequency of fast food/junk food consumption [33]. The validity of questionnaire was approved by a panel of faculty members of Guilan University of Medical Sciences. The frequency of junk food consumption rated on a scale from 1=Never to 9=More than once per day.

The frequency of junk food consumption based on type (sweetand carbonated drinks, energy drinks, fruit-flavored drinks, fast food meals, fried foods, sweet and salty snacks) was assessed in the range of “never” to “more than 4 times per week or every day”. The frequency of junk food consumption was divided into two categories: moderate level (less than median including score zero) and high level (more than median including score 1). The median was determined with a score of 5 indicating “once a week”. The frequency of exposure to food advertisement was rated as “rarely”, “from time to time”, “quite often”, “very often”. The source of exposure to food advertisement was evaluated based on the platforms of advertisement (TV, radio, school, newspaper, magazine, Internet and social networks, outdoor billboards/public places, and more than one source).

Data were collected in four days from November 27 to December 4, 2016. The questionnaires were completed within 20 minutes by the subjects. After collecting data, they were analyzed in SPSS V. 21 softwareusing descriptive and inferential statistics. Since the level of junk food consumption was a ranked variable, Kruskal-Wallis test was used to compare the difference in junk foodconsumption frequency based on thefrequency and source of exposure to junk food advertisement.

Results

As shown in Table 1, most of the subjects were female (52.2%) and 11th grade students (37.5%). In terms of the frequency of exposure tojunk food advertisement, 37.2%, 33.4% and 15.3% of subjects reported “from time to time”, “quite often” and “very often”, respectively. Moreover, 51.9% of samples were exposedto more than one source of junk food advertisement. TV was reported as the most common source of exposure to junk food advertisement (19.9%). Regarding the frequency of junk food consumption, 0.6% reported never, 22.6% less than once a month, 8.8% once a month, 11.7% once a fortnight, 19.4% once a week, 21.7% 2-3 times per week, 5.9% 4-6 times per week, 3.8% once a day, 5.6% more than once a day. In terms of the junk food type, sweet snacks (27.3%), fried foods (11.7%), salty snacks (11.4%), sweet and carbonated drinks, energy drinks, fruit flavored drinks (5.3%), and fast food meals (4.4%) were consumed by the students more than 4 times per week or every day by subjects.

The Kruskal-Wallis test results, shown in Table 2, indicated that a significant difference between the frequency of junk food consumption and the frequency of exposure to junk food advertisement (P=0.0001). This means that the more frequent junk food advertisement viewing can be associated with more frequent consumption of junk foods.

Discussion

In this study, nearly half of subjects were exposed to junk food advertisement “quite often” and “very often”, which isconsistent with the result of Esmi et al. who reported that the most of children and adolescents viewed TV commercials “sometimes”, “always” and “very often” [34]. In the study of Hovington, majority of adolescents were exposed to junk food advertisement “quite often” and “very often” [35]. Moreover, our results showed that more than half of subjects had been exposed to more than one source of junk food advertisement. TV was mentioned as the most common source of exposure to food advertisement. This is in agreement with the results of Joseph et al. who showed that TV was the most popular source of information about fast foods [14].

After TV, the internet/social networks and school were the most common source of junk food advertisementin our study according to the report of students, but none of them reported the radio as a source of exposure. It can be related to low usage rate of the radio by this age due to reduced popularity and also lower focus of food industries on the radio advertising due to the lack of attractive images and light/color techniques to attract children and adolescents. In the study of Hovington, TV, outdoor billboards and public places were the most common sources [35]. This indicates the focus of food industries on attracting adolescents throughthe visual techniques, and the important effect of the media on adolescents’ eating habits.

Based on the frequency of junk food consumption, our resultsshowed that few subjects reported “once a day” more than once a day”; while the study results of Ritchie [36] Akman et al. [37] and Jaisheeba et al. [38] were in reverse. This discrepancy may be due to differencein junk food definition, living environment, eating habits, and data collection methods. Similar studies have shown the high intake of junk food in urban areas especially among adolescents and young people. Although the junk food consumption rate among high school students was noticeable in this study, but incomparison withother similar studies,the reported rate was lower.

Furthermore, the results showed that a significant difference in junk food consumption frequency based on the frequency of exposure to food advertisement. This indicates that the higher exposure to junk food advertisement can be associated with higher consumption of junk foods. Kuhi et al. also found a significant and positive association between exposure to advertisements and fast food consumption; those who were more exposed to advertisements, had eaten more fast food [39]. In the study of Purushothamanet al., all of adolescents reported that advertisements influenced them to eat more junk foods [40]. According to the results of current study and other similar studies, it can be stated that the media and their food advertisement have very important role in adolescents’ eating habits.

In this study, the median and mean of junk food consumption frequency in adolescents exposed to more than one advertising source were more than others. The highest frequency of junk food consumption was reported by adolescents who had been exposed to only one advertising source including school, internet/social networks and TV, respectively. However, there was no statistically significant difference in the median of junk food consumption frequency and source of exposure to food advertisement.

The results of Scully et al. [20] and Yarmohammadi et al. [41] showed a significant association between the time of viewing TV commercials and fast food consumption rate. Our results also showed that, compared to students with no exposure to digital advertisement, exposed students had higher consumption of junk foods. Kuhi et al. concluded that advertisement was the most important variable effecting students’ tendency towards fast food consumption [39].

Nowadays, there are numerous local and satellite TV channels that make programs especially for adolescents who are spending more time on social networks and surfing Internet. On the other hand, makin ghighly paying advertisement is one of the best ways tosurvive for these programs. Therefore, the adolescents who have view these programs have higher rates of fast food consumption. So, it is necessary to control media advertising and makes a framework for monitoring the food advertisement.

Some of the study limitations were using a self-report questionnaire, recall bias, and collecting data during the academic year which can influence the outcome. It is recommended that further studies be conducted using different sources of data and a larger sample size over a wider time range.

Ethical Considerations

Compliance with ethical guidelines

The participants were informed about the study objectives and an informed consent form was signed by them and one of their parents; they were also assured of theconfidentiality of their information. Moreover, they were allowed to leave the study at any time and the study results would be available tothem. This study obtained its ethical approval (Code: IR. GUMS. REC. 1395. 257) from Guilan University of MedicalScience.

Funding

This paper was extracted from the master thesis of the first author approved by the Research Committee of Guilan University of Medical Sciences in Rasht, Iran. This study was financially supported by this university.

Authors contributions

Conceptualization: Saeid Moradi Latreyi and Leila Mirhadyan; Manuscript draft preparation: Afsaneh Pasha and Leila Mirhadyan; Statistical analysis: Ehsan Kazemnezhad Leili; Review and editing: All authors.

Conflict of interest

The authors declared no conflicts of interest.

Acknowledgements

The authors would like to thank the Social Determinants of Health Research Center, Guilan University of Medical Sciences, and the faculty members of the Nursing Department at Guilan University of Medical Sciences, as well as the staff of the studied high schools.

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