INTRODUCTION Social and economic transformations resulting from the emergence of globalization and industrialization have resulted in changes in food consumption. In Brazil, the concern was initially focused on energy deficiency and nutritional deficiencies, but in recent years it has turned to overweight, obesity and, consequently, to chronic non-communicable diseases (NCDs) ¹ . The intake of natural or minimally processed foods has been reduced, while fast foods, soft drinks, sweets and snacks rich in sugar, fat and preservatives have become part of the population’s diet ² . According to the World Health Organization – WHO (1995), adolescence marks the transition from childhood to adulthood, between the ages of 10 and 19 ³ . This is a period characterized by intense physical changes related to puberty, cognitive changes, and psychosocial transformations, and ends with the insertion into adult society ⁴ . It is during this period that eating habits are consolidated, where changes in food consumption occur due to physiological changes and the influence that the social environment exerts on adolescents ⁵ . Among young people, inadequate eating habits are characterized by excessive consumption of sugars, fats, preservatives, and sodium from ultra-processed products, associated with low consumption of fruits and vegetables, favoring weight gain and the emergence of diseases ⁶ . Adolescents are also more susceptible to the influence of the media, which imposes thinness as beauty standards, resulting in negative consequences for food consumption. In order to stay within the standards, they skip important meals such as breakfast or dinner, resulting in low energy and nutrient intake ⁷ . Therefore, they represent a nutritionally vulnerable group, since they have high energy needs, and their eating habits, lifestyle and environmental factors make them more susceptible to NCDs ⁸ . Socioeconomic factors such as parental education and family income are related to the food consumption of adolescents. Those who have better economic conditions have more access to foods with low nutritional value and high caloric density, while in low-income families the consumption and quantity of these foods is higher ⁹ . Inadequate nutrition is one of the most relevant risk markers associated with the current epidemic of chronic noncommunicable diseases, which are the main cause of mortality in Brazil ¹⁰ . Given the complexity of socioeconomic and cultural factors in adolescents’ eating habits, it is necessary to expand public policy actions that can intervene in the determinants of these factors. In this perspective, in order to understand the consumption profile of adolescents and support actions to be implemented and/or reformulated as a measure to promote the health of this population group, this study aimed to evaluate the consumption of ultra-processed foods among adolescents from the 6th to 9th grades of the public school system in Montes Claros – MG. MATERIALS AND METHODS This study is part of the research project entitled “Health in Schools”. This is a quantitative, descriptive and cross-sectional study, carried out with adolescents of both sexes, enrolled in the last four grades of elementary school in municipal public schools in Montes Claros – MG. Montes Claros is a medium-sized city, located in the north of the state of Minas Gerais, Brazil, and represents the main urban center of the region. According to the Brazilian Institute of Geography and Statistics (IBGE) in 2018, the estimated population for 2017 was around 402,027 inhabitants. Montes Claros has 33 municipal public schools in the urban area for elementary school II, with approximately 4,231 students enrolled in 2017. The following parameters were considered to calculate the sample: event prevalence of 50%, 95% confidence level, and standard error of 5%. A correction for the design effect (Deff=2.0) was adopted and an increase of 20% was also established to compensate for possible lack of responses and losses. The participation of at least 750 adolescents was estimated. The inclusion criteria for adolescents were those who were regularly enrolled in the 6th to 9th grade of elementary school, and the signing of the TCLE, demonstrating the consent of the students and their parents/guardians for the students to participate in the research. Students who were not present on the days of data collection, pregnant women and those with chronic debilitating diseases such as chronic anemia, heart failure, severe asthma, those with genetic syndromes and hypothyroidism, or those on chronic use of corticosteroids were excluded from the study. Before starting the research, a pilot study was conducted with adolescents of both genders in order to improve the instruments and methodological procedures. Data collection was carried out in 2017 within the schools during the school day. A team of trained health academics aligned with the methodology carried out the procedure. Initially, the adolescents were informed about the study and verbally questioned about their consent to participate in the research. Those who agreed to participate received a “consent form” to be completed by their parents or guardians and an “assent form” to be completed by the student themselves. One of the instruments used in this study was a structured, self-administered questionnaire containing the demographic variables: gender, age group and grade. In addition, a Food Frequency Questionnaire (FFQ), used to assess the frequency of daily consumption of at least one group of Ultra-Processed Foods (UPF). The variable was investigated based on the question: “In the last 7 days, on how many days did you eat…?”, for each of the following foods/food groups: sweets, soft drinks, processed meats (burgers, sausages, mortadella, salami, ham, nuggets or hot dogs), and packaged snacks. Daily consumption of at least one UPF group was determined by the affirmative answer to the consumption of at least one of the groups on all seven days of the week investigated. First, the frequencies of food consumption of ultra-processed foods in the last week were calculated. Then, the prevalence of frequency of regular consumption was obtained, as well as their respective 95% confidence intervals (95%CI). The chi-square test was used to assess possible differences between the exposure categories. For all analyses, a significance level of 5% was considered. The statistical treatment of the collected information was performed using the Statistical Package for the Social Sciences (SPSS) software, version 20.0. To characterize the sample, descriptive statistical analysis of simple frequencies (n) and percentages (%) were used. This research met the ethical precepts established by Resolution no. 466/2012 and was approved by the Human Research Ethics Committee of the State University of Montes Claros (CEP), under protocol number 1,908,982. RESULTS The study included 1,475 adolescents with a mean age of 13.00 ± 1.34 years, of which 50.1% (n = 739) were female and 49.9% (n = 736) were male. Most of the interviewees were enrolled in the 7th grade of elementary school (Table 1). Table 2 shows the distribution of the weekly frequency of consumption of ultra-processed foods among the adolescents evaluated. It was observed that processed meats and soft drinks were consumed weekly by 77% of the students, with 33.7% and 12.5% ​​consuming sweets and soft drinks daily, respectively. It was also recorded that almost half of the students (44.2%) had not consumed packaged snacks in the week prior to the study. Figure 1 reveals that high proportions of ultra-processed food consumption were found among adolescents in the seven days prior to the study (61.2%). Among these, the most consumed were sweets, followed by soft drinks, processed meats and packaged snacks (48%, 23.5%, 19% and 13%, respectively). Table 3 presents the analysis of the frequency of regular consumption of ultra-processed foods according to sex and age group. It was observed that the regular consumption of sweets and packaged snacks was significantly associated with sex, being more prevalent in females (P<0.001). The prevalence of regular consumption of UPF was also higher among females (p=0.002). Regarding regular consumption according to age group, higher prevalences were observed in adolescents aged 13-14 years (p=0.041). DISCUSSION Adolescence promotes greater autonomy in making one’s own decisions about eating behavior, which can negatively influence lifestyle. Social interaction becomes more important, interfering in the formation of eating habits and, therefore, behavioral changes tend to occur at this stage ¹¹ . Such changes are related to the high intake of processed products and the decrease in the consumption of natural foods . Currently, there is a rapid increase in these changes in eating behavior in underdeveloped countries, which are undergoing economic, social and technological changes, resulting in greater purchasing power, which facilitates access to ultra-processed foods ^12,2 . Studies carried out by Monteiro et al. in 19 countries found that 26.4% of the total energy in the participants’ diet came from processed foods. In Portugal and Italy, the average household availability of ultra-processed foods was 10.2% and 13.4%, respectively; in Germany, 46.2% and the United Kingdom, 50.4%. This same study revealed an association between the availability of ultra-processed foods and obesity among adults ¹³ . In Brazil, in a study conducted by Louzada et al., individuals with high consumption of ultra-processed foods had a significantly higher body mass index and were more likely to develop obesity when compared to individuals with low consumption ¹⁴ . The present study revealed high consumption of at least one food from the UPF group. Costa et al. investigated the regular intake of four groups of salty UPF among adolescents. Daily consumption of at least one UPF group was reported by almost 40% of the students, and the highest percentage was observed among females (51.3%) ¹⁵ . Another study conducted with adults from Pelotas by Gigante et al., demonstrated that the intake of ultra-processed foods contributed to more than 50% of the total calories consumed by the participants, with a higher prevalence among females ¹⁶ . The pattern of sweets intake was marked by high consumption, characterizing it as an unhealthy eating factor. Correa et al. identified a similar eating pattern among adolescents, with 41.3% consuming sweets on five or more days a week, where cookies and soft drinks were consumed by 35.1% and 33.2% of participants, respectively ¹⁷. Inadequate eating habits among adolescents may be related to the frequency with which they eat out, skip meals, or replace them with easily accessible industrialized preparations such as fast food ⁵ . Messias et al., evaluated the consumption of ultra-processed foods by students in the public school system and found high rates of products with high sugar and sodium content. Among the processed foods rich in sodium most cited by both sexes are sausages and pizzas (1,117.3 mg on average and 736.7762 mg, respectively). Those with high sugar content are chocolate powder and stuffed cookies representing 77.39 g and 40.62 g, respectively ¹⁸ . Inadequate diets and a sedentary lifestyle are associated with the emergence of diseases such as obesity, diabetes, cardiovascular disease, hypertension, and cancer. This is an alarming factor, considering that adolescence is an important phase of growth and development ¹⁶ . Although similarities were found with the dietary pattern reported by other authors, the comparison of the present study with others should be carried out carefully due to the differences in the characteristics of the studied population and in the instruments used to assess the dietary pattern. This study has limitations arising from the dietary record, such as underestimation of food consumption and/or modification of habitual consumption in the days prior to the research. The present study contributes to other findings in the literature and its results reflect the need to monitor the food consumption of ultra-processed foods, and reinforce the need for public policy actions aimed at food and nutrition that emphasize the reduction in the consumption of UPF. CONCLUSION This study showed high prevalence of regular consumption of ultra-processed foods among adolescents enrolled in the public school system of Montes Claros. Among the ultra-processed foods analyzed, sweets with the highest weekly consumption record stand out. The highest prevalence of regular consumption of UAP was found among female adolescents aged 13-14 years. Considering this scenario, it is necessary to raise awareness among adolescents about the consequences of excessive consumption of ultra-processed foods, through actions to promote healthy eating in the school environment. Such strategies are essential to prevent the intake of unhealthy foods from continuing into adulthood and, consequently, causing chronic non-communicable diseases. NOTE Funding source: Voluntary Scientific Initiation Program (ICV) of the State University of Montes Claros (Unimontes), Institutional Program of Scientific Initiation Scholarships for Medical Education – PIBIC/EM, National Council for Scientific and Technological Development (CNPq), to the Scientific Initiation Program with Scholarship (PROIC BOLSA) of the Ibituruna School of Health (FASI).