2.2 Data collect
The study was conducted between August 2018 and February 2020 and included 101 participants; however, for the present analysis, we excluded 5 participants due to not having any blood pressure measurements at follow-up.
Children and their guardians participated in individual consultations and standardized monthly educational activities based on the 10 steps of the Food Guide for the Brazilian Population. The guidelines included changes in the family's behavior in relation to food choices and purchases, with a focus on quality, encouraging a reduction in the consumption of UPF.
Data collection for the present study took place at baseline and the second, fifth, and sixth-month follow-up. The research assistants responsible for the collection were trained in order to standardize data measurement and ensure reliability.
Outcome
Blood pressure was measured at all appointments, with a digital monitor HEM-742 (Omron Healthcare Inc.), previously validated for use in adolescents13, on the right arm supported at the level of the heart, using an appropriate cuff size, with the child sitting with feet on the floor and at rest for 5 minutes before measurement14,15. Two measurements were taken, with a minimum interval of 2 minutes, and the average was calculated. If the difference between the 2 measurements was equal to or greater than 5 mmHg, a third measurement was performed.
The SBP and DBP values obtained in mmHg were transformed into a Z score, using the mean and standard deviation of the blood pressure values of the American pediatric population, according to sex, age, and height in Z score15.
Blood pressure was classified based on sex, age, and height as normotension, if SBP or DBP values < 90th percentile; prehypertension, if SBP or DBP ≥ 90th and < 95th percentile or SBP ≥ 120mmHg or DBP ≥ 80mmHg; and, hypertension, if the SBP or DBP ≥ 95th percentile15.
The models were tested to assess the variation of systolic and diastolic blood pressure over time, using blood pressure measurements in mmHg and Z score.
Exposure
Food consumption was assessed using a 24-hour dietary recall (R24h) performed at each visit, using netbooks equipped with a program based on the multiple-pass method and developed to evaluate the food consumption of Brazilian adolescents16. Respondents provided detailed information on all foods and beverages consumed in the 24 hours: meal occasion, time, place, and amount of food in household measures. The reported amounts of food were converted into grams or milliliters, and then the nutritional composition was estimated using the Brazilian Table of Food Composition (TACO), of the State University of Campinas17.
The nutritional composition of local preparations was calculated based on the individual components of each preparation, according to information in technical publications from teaching and research institutions. For every 100 grams of edible parts of foods and preparations, total energy (kcal), UPF energy (kcal), sodium (mg), and potassium (mg) values were calculated. Food intake was also classified based on NOVA food classification, defining each food and beverage into 1 of the 4 food groups based on their extent and purpose of industrial food processing: (1) Unprocessed or minimally processed foods; (2) Processed culinary ingredients; (3) Processed foods; (4) Ultra-processed foods18.
Through the sum of energy and grams of food items included in each group, it was possible to calculate the relative contribution of each group to the total daily energy value.
Urinary casual samples were collected at the clinic after 12 hours of fasting, for sodium and potassium measurements at three times: baseline, in the second and fifth- month follow-up. Urinary sample analyzes were performed at the hospital's clinical laboratory. The Na/K ratio was calculated using sodium and potassium concentrations (mEq/L).
Covariates
The independent variables used in this study were age (years), race/skin color self-reported (black, white, light-skinned black, Asian or indigenous), weight, and height.
Body weight was measured using a portable electronic scale (Tanita BC-558) and height was measured in duplicate using a portable anthropometer (AlturExata). Both measurements were taken at each visit, with the children barefoot, wearing light clothing, with their arms extended along the body, and positioned in the Frankfurt horizontal plane19.
The classification of nutritional status was based on body mass index (BMI) values for age, in z-scores, according to sex, based on the curves proposed by the WHO20. BMI for age was calculated using the WHO AnthroPlus software20, and the values obtained were classified according to the cutoff points recommended for children aged 5 to 19 years: low weight (BMI for age <-2 z-scores ), eutrophic (BMI for age ≥ – 2 and ≤ + 1 z-scores), overweight (BMI for age > + 1 and ≤ + 2 z-scores), obese (BMI for age > + 2 and < + 3 z-scores), and severely obese (BMI for age > + 3 z-scores).
The project was approved by the Research Ethics Committee of the Pedro Ernesto University Hospital (CAAE: 87593118000005259). The Informed Consent Form was signed by the child's parents or legal guardians and the children signed the Informed Assent Form.