The prevalence of obesity is one of the main public health problems worldwide, reaching 18% among young people between 5 and 19 years of age in 2016. One possibility of effective treatment can be the Mediterranean diet (MD). Therefore, it is proposed to carry out a nutritional intervention based on this diet to more effectively reduce obesity in adolescents. The main purpose of this multicentre study is to assess whether an energy-restricted Mediterranean-style diet (MD) intervention including healthy products from the Mediterranean basin (mixed nuts, pomegranate and hummus) and sourdough bread is more effective against obesity and associated CVD risk factors than a conventional low-fat diet carrying out a multicentre nutritional and clinical intervention study specifically targeting obese/overweight adolescents (13-17y) from different Mediterranean countries; all combined with an educational web-application designed to encourage healthy behaviours.

It is a multicenter, randomized, controlled intervention study conducted with adolescents with obesity/overweight ≥90 percentile who do not suffer from any chronic disease. 240 subjects will be recruited from three Mediterranean countries: Italy (Parma), Portugal (Coimbra) and Spain (Reus), specifically 80 participants per country, 40 adolescents as an intervention group and 40 as a control group, in Reus. The intervention study is scheduled to begin in January 2021.

The intervention group will receive a diet based on the characteristics of MD, and will be reinforced with satisfying and healthy Mediterranean foods such as sourdough bread (2 servings of 50-60g / day), squeezed pomegranate (4 servings of 200ml / week), hummus/chickpeas (2 portions of chickpeas of 150-200g / week, one in hummus format) and mixed nuts (4 servings of 30g / week); and the control group will receive a recommended diet based on the consumption of low-fat foods. A caloric restriction of 20% of the total energy requirements will be applied to both groups in adolescents with BMI ≥95 percentile (obesity) and a caloric restriction <20% of the total energy requirements will be applied in adolescents with BMI ≥90 to <95th percentile according to overweight (gender/age / physical activity). The diet will be applied for 4 months in both groups. Adolescents from both groups will be given a motivational interview and will be provided with an educational website that will be used during the intervention, through which they will learn.

The principal outcome is BMI z-score, a standardized measure of BMI based on the specific age and gender norms. The effectiveness of the intervention will be evaluated by comparing the BMI z-score between the control (low-fat diet) and intervention (MD) groups.

The secondary outcomes are: Adherence to the DM, KidMed questionnaire; Level of physical activity, PAQ-A questionnaire; Habit/food intake: 3-day dietary record, Helena study food frequency questionnaire, Knowledge about food and nutrition, a questionnaire from Helena's study; Quality of life, kid screen-27 Index; Sociodemographic data of the parents; Anthropometric data: weight, height, BMI, body composition, waist circumference, waist-hip ratio; Clinical variables: blood pressure, Biochemical variables and omic determinations: in urine, blood and feces.

In total, the adolescents will receive 5 visits:

• 1 pre-selection visit (to check inclusion / exclusion criteria in the study) (V0)
• 1 inclusion visit (V1) in which stool, urine, and blood samples will be collected, anthropometric measurements (such as weight and waist circumference) and blood pressure will be taken, and questionnaires and records will be answered dietary.
• 1 follow-up visit (V2), at 2 months, in which anthropometric and blood pressure measurements will be taken and questionnaires and dietary records will be answered.
• 1 final visit (V3), at 4 months, in which stool, urine, and blood samples will be collected, anthropometric and blood pressure measurements will be made, and questionnaires and dietary records will be answered.
• 1 post-intervention follow-up visit (V4), 4 months after the end of the intervention, in which anthropometric and blood pressure measurements will be taken and questionnaires and dietary records will be answered.

Inclusion Criteria:

• boys and girls aged 13-17 years
• having obesity, defined as an age- and sex-specific BMI in the 95th percentile or greater (1), or great overweight (age- and sex-specific BMI in the ≥90th to <95th percentile),
• having informed consent (sign by both, one parent and the adolescent),
• and to have a mobile phone with internet access.

Exclusion Criteria:

• having diabetes and other metabolic, endocrine and chronic disorders;
• intake of antibiotics, drug, probiotics or nutritional supplements in the last month;
• prescribed medicine to control hypertension, inflammation or dyslipidemia,
• following a prescribed diet for any reason, including weight loss, in the last 3 months;
• following a religion-restricted diet;
• and having allergies or food intolerances in: nuts, pomegranate, bread and/or chickpeas.

The data will be shared with other researchers involved in the MED4Youth study

Study protocol will be published in a scientific international journal. Clinical Study Report will be published at the end of the study.

Data will be only shared with the researchers involved in the study. Protocol and results will be shared with scientific community

Due to the nature of the study, the participants cannot be blinded to the intervention, although the investigators who will perform the sample and data analysis will be blinded.