Journal of Clinical Nutrition & Dietetics

Keywords

Diet Quality Index-International (DQI-I), Mediterranean diet, Adolescents, Balearic Islands.

Introduction

The Mediterranean diet (MedDiet) includes high amount and frequency consumption of vegetables, fruits, cereals (preferably as whole grain), legumes, nuts and olive oil; moderate consumption of fish and shellfish, white meat, eggs and dairy products; small quantity and frequency consumption of red meat, processed meats, and foods rich in sugars and in fats; and a regular but moderate intake of wine, generally during meals. However, epidemiological evidences suggest that dietary patterns in the Mediterranean countries are changing rapidly, with an increased consumption of animal products and saturated fat and a decline of intake of basic foodstuffs based on vegetables [1].

The MedDiet has been quantified in diet indices that attempt to make a global evaluation of the quality of the diet based on a traditional MedDiet reference pattern. Diet indexes are known as ‘a priori’, as they are built based on dietary guidelines or recommendations, and ‘a posteriori’, as they consists in defining food patterns once the dietary data are collected and using specific statistical analysis [2]. Referring to the ‘a priori’ defined diet indices, a Mediterranean adaptation of the Diet Quality Index-International (DQI-I) was previously stated assessing the diet of young people in southern Spain [3], following the Tur et al. [4] modification of the method developed by Kim et al. [5]. The Mediterranean DQI adaptation focuses on four aspects of high-quality diet (i.e. variety, adequacy, moderation and overall balance). Specific diet components are assessed under each category. Variety is evaluated as overall variety and as variety of protein; adequacy evaluates the intake of those dietary elements that are required to protect against under-nutrition and deficiency disorders; moderation evaluates the intake of food and nutrients related to chronic diseases, which may need restriction; and overall balance examines diet in terms of proportions of energy sources and fatty acid composition [3-5]. These categories help users to identify aspects of their diet that may need improvement.

Because there is evidence that nutritional behaviors track from adolescence into adulthood, the promotion of healthy nutrition during adolescence has the potential to confer significant longterm health benefits [6]. The aim of the present study was to assess the diet quality of Mediterranean adolescents by means of the DQI’s Mediterranean adaptation, and its association with socioeconomic, anthropometric, lifestyle and body image characteristics.

Material and methods

The study is a population-based cross-sectional nutritional survey carried out in the Balearic Islands (2007-2008) that has been described in detail elsewhere [7-10]. Briefly, a multicenter study was performed on Balearic Islands’ adolescents aged 12–17 years. To calculate the number of adolescents to be included in the study in order to guarantee a representative sample of the whole Balearic Islands, we selected the variable with the greatest variance for this age group from the data published in the literature at the time the study was planned; that was body mass index (BMI) [8]. The sampling was determined for the distribution of this variable; the confidence interval (CI) was established at 95% with an error ±0.25. The established number of subjects was 1,500. The total number of subjects was uniformly distributed in the cities and proportionally distributed by sex and age group. The final number of subjects included in the study was 1,231 adolescents (82% participation). The reasons to not participate were (a) the subject declined to be interviewed, and (b) the parents did not authorize the interview.

This study was conducted according to the guidelines laid down in the Declaration of Helsinki, and all procedures involving human subjects were approved by the Balearic Islands’ Ethics Committee (Palma de Mallorca, Spain) no. IB-530/05-PI. Written informed consent was obtained from all subjects and also from the next of kin, caretakers, or guardians on the behalf of the minors participants involved in the study.

Dietary assessment

Dietary questionnaires included two non-consecutive 24-hour diet recall periods, one in the warm season (May-September) and one in the cold season (November-March) to account for the influence of seasonal variations, and a semi-quantitative food-frequency questionnaire (FFQ) that has previously been validated [11], applied in other studies and surveys over the Spanish population [12-16] and previously described [8,10]. Conversion of food into nutrients was made using a self-made computerized program (ALIMENTA^®; NUCOX, Palma, Spain) based on Spanish [17,18] and European [19] food composition tables, and complemented with food composition data available for Majorcan food items [20]. In adolescents, increased energy requirements, unstructured eating, concerns with self-image and rebellion against authority may all contribute to poor reported food intake [21]. In studies of both sexes presented separately, females underreported more than males with means ± standard deviation (SD) for energy intake (EI): energy expenditure of 0.85 ± 0.15 and 0.92 ± 0.15, respectively. In the present study, identification of misreporters was conducted on the basis of the ratio of EI to basal metabolic rate (BMR). In spite of BMR is the minimal rate of energy expenditure per unit time at rest, EI: BMR <0.92 (boys) and <0.85 (girls) was considered to represent underreporting [21], while EI: BMR≥2.4 was considered to represent over-reporting [22,23] since few data are published about overreporting. Under-reporters (20%) and over-reporters (2%) were excluded from the analysis [8].

Mediterranean adaptation of the International Diet Quality Index

The diet quality was evaluated using the Mediterranean adaptation of the DQI-I described elsewhere [3]. Briefly, the DQI focuses on four aspects (i.e. variety, adequacy, moderation and overall balance) under each of these categories there are specific components of diet that are assessed (Table 1). The scores for each component is the sum of the scores for each component in that category. The total DQI-I score (range 0-100 points) is the sum of the scores for the four categories. The scoring system is described in detail in Table 2.

Table 1: Diet Quality Index-International (DQI-I) scores and components.

Table 2: Components of the Diet Quality Index (DQI-I) and percentage of sample in component subcategories.

Assessment of other co-variables

Socioeconomic factors and dietary habits

Socioeconomic factors were recorded using a questionnaire that included age group; parental education level (according to years and type of education: low, <6 years; medium, 6–12 years; high, >12 years); and parental profession level (based on the occupation of parents and classified as low, medium and high, according to the Spanish Society of Epidemiology) [24]. The number of daily meals and snacks was calculated from the total eating occasions that participants declared among the following: breakfast; midmorning snack; lunch; mid-afternoon snack; dinner; before going to sleep; others. Three groups of eating frequency were considered: ≤3, 4 and ≥5 times/day [7,8,10]. Distraction during mealtime was also studied using different possibilities: (1) watching TV; (2) listen to the radio; (3) get up from the table; (4) conversation during mealtime. These variables were joined and expressed as (1) attention to mass media (TV + radio); (2) others [7].

Anthropometry measurements

Height was determined using a mobile anthropometer (Kawe 44444, Asperg, Germany) to the nearest millimeter, with the subject’s head in the Frankfurt plane. Body weight was determined to the nearest 100g using a digital scale (Tefal, sc9210, Rumilly, France). The subjects were weighed in bare feet and light underwear. The subjects were asked to stand erect in a relaxed position with both feet together on a flat surface. Triceps and subscapular skinfold thickness (ST) were measured at the right side of the using a Holtain skinfold calliper (Tanner/ Whitehouse, Crosswell, Crymych, UK), and the mean of three measurements was used. Height and weight measures were used to calculate body mass index (BMI, kg/m²). Body fat percentage (%BF) was measured from triceps and subscapular ST according to Slaughter et al. (1988) [25]. This equation has been proposed as the most accurate for estimation of %BF from ST in this particular population of adolescents [26]. %BF and height were used to calculate fat mass index (FMI; kg/m²).

Defining overweight and obesity

Adolescents were classified into three groups as follows: (i) normal-fat (BMI for age and sex <25 kg/m²; FMI<4.58 kg/m² in boys, FMI<7.76 kg/m² in girls); (ii) overweight (BMI for age and sex ≥25-<30 kg/m²; FMI≥4.58 kg/m² in boys, FMI≥7.76 kg/m² in girls); (iii) obesity (BMI for age and sex ≥30 kg/m²; FMI≥4.58 kg/ m² in boys, FMI≥7.76 kg/m² in girls). The variable was labeled as ‘body composition’ [8,9,27]. Age- and sex-specific BMI cut-offs were used according to the International Obesity Task Force and Cole et al. (2000) definitions [28], and FMI cut-offs according to Alvero-Cruz et al. (2010) [29] criteria for adolescents: 4.58 kg/m² in boys and 7.76 kg/m² in girls, as the limit between normal-fat and overfat.

Assessment of physical activity

Physical activity was evaluated according to the guidelines for data processing and analysis of the international physical activity questionnaire (IPAQ) [30] in the short form, and its specific modification for adolescents (IPAQ-A) [31]. The specific types of activity assessed were walking, and moderate (i.e. physical activity at school), and vigorous (i.e. sport practice) activity. According to the AVENA (Alimentación y Valoración del Estado Nutricional en Adolescentes: Food and Assessment of Nutritional Status of Adolescents) study [32], the questionnaire also included information on television (TV) viewing, computer use and video games to the nearest 10 min. Sedentary behaviour was established with a cut-off level of 300 min of moderate/vigorous physical activity per week [27,33].

Body image

Perceived body image was measured using the Stunkard scale [34], which consists of silhouette drawings ranging from 1 to 9 with monotonic increments in overweight percentage where 1 is the leanest and 9 is the heaviest. Separate figures for boys and girls were used. Participants were asked to identify of the 9 body figures: (a) ‘Which silhouette looks most like yourself?’ and (b) ‘Which silhouette would you like to look like?’ The difference between perceived body image and desired body image was used to determine the level of dissatisfaction with current body image [10]. Values other than zero represent dissatisfaction with perceived body image. A positive value was indicative of the participant’s desire to be thinner than his/her perceived current size, while a negative value reflected the participant’s desire to be thicker than his/her current perceived size [10].

Statistics

Analyses were performed with Statistical Package for the Social Sciences version 21.0 (SPSS, Inc., Chicago, IL, USA). Scores of the Mediterranean modified DQI-I and its four main categories were expressed as the mean and score obtained for each component of the DQI-I, and the percentage of the population for each component subcategory was calculated. ANOVA, univariate and multivariate linear regression analysis were used to assess the association between modified DQI-I scores and values of socioeconomic, dietary habits, lifestyle, anthropometric and body image variables. The level of significance was established for P values <0.05.

Results

Characteristics of participants have been previously published elsewhere, and means and SD are corresponding to the data of population [7,8,27]. The mean total modified DQI score was around 47.0% (SD: 9.8%) of the possible score (100%). The best achieved score was for the variety one, followed by the adequacy and moderation scores. Overall balance was the weakest area of the diet (Table 1). Regarding the variety category, only 15.2% of adolescents daily consumed at least one serving from each food; 31.5% missed only one food group and 36.8% missed two food groups; and only 18.1% had also three or more different sources of protein per day (Table 2). According to the adequacy category, a large proportion of the population reported an intake of fibre, proteins, iron and vitamin C over 50% the recommendations; about half the population reported an intake of fruit group, grain group, and calcium over 50% the recommendation; and most of adolescents failed to meet the recommended levels of vegetables intake. According to the moderation category, only 10.6% and 3.0% of adolescents achieved the fat (≤30% of total EI) and saturated fat goals (≤7% of total EI), respectively. Cholesterol intake was ≤300 mg/d in 45.7% of the population. Moreover, only 2.1% of adolescents consumed empty-calorie foods less than five times a week. A very poor balance was also found for energyyielding nutrients as well as among fatty acids.

The univariate linear regression analysis showed that age and media screen time were inversely correlated with the DQI score; whereas a direct correlation with parental educational level was found (Table 3). The DQI score also decreased in physically inactive adolescents and in those adolescents who wish a thicker body shape; whereas increased in those adolescents who wish a thinner body shape. No association between sex, parental socioeconomic status, body composition, daily meals & snacks, breakfast habit, and attention to mass media with DQI score were found. The multivariate linear regression also showed that age group (β = -1.087, SEM β = 0.509, P = 0.033), parental educational level (β = 1.098, SEM β = 0.490, P = 0.025), media screen time (β = -1.923, SEM β = 0.519, P < 0.001) and body image dissatisfaction (β = -1.346, SEM β = 0.561, P = 0.017) were the main associated variables with the DQI score (data not shown).

Table 3: Association between Diet Quality Index (DQI-I) and sociodemographic and body image variables.

Discussion

The adaptation of the DQI-I by Mariscal-Arcas et al. [3] was used to assess the diet quality in a representative sample of a Mediterranean adolescent population with the aim of ascertaining possible nutritional problems related to the nutrition transition that may be appeared, which is especially common among young generations. The mean DQI score obtained for the Mediterranean adolescents was 47% of the full score, which is more lower than the mean scores reported in the USA and China in 1993-96 (≥20 years old) [5] and also southern Spain in 1999-2000 (6-18 years old) [3], but higher than mean scores observed in adult Balearic Islands’ population (16-65 years old) in 1999-2000 [4]. According to the criteria of Kim et al. [5], scores below 60% indicate a poorquality diet, but it is arguable whether DQI-I criteria for highquality diets are wholly applicable to Mediterranean-type diets [3,4]. To assess adolescents’ diet quality, data from the HELENA (Healthy Lifestyle in Europe by Nutrition in Adolescence) study were also included into the Diet Quality Index for Adolescents, including a specific Meal index (DQI-AM) [35]. The DQI-AM consisted of the arithmetic mean of four components: diet quality, dietary diversity, dietary balance and meal frequency and ranged from -25 to 100%. The DQI-AM score is not comparable with our data, however, the mean overall DQI-AM score and the scores of all its components were higher in southern Europe than in northern Europe, with exception of the DQI meal component [35].

In the present population, variety and adequacy had the highest scores as also found in adult Balearic Islands’ population [4] and in children and adolescents in southern Spain [3]. In the HELENA study, DQI meal and DQI diversity had the highest scores [35].

Variety. Variety in the diet was evaluated as overall variety and variety within protein sources. The DQI-I assumes that a diet including various protein sources is also a feature of a good varied diet [3]. However, the studied adolescent population is undergoing a change in dietary patterns [8] and protein variety may be associated to changes in traditional protein sources.

Adequacy. Adequacy reflects compliance with prevailing recommendations to ensure a healthy diet. The diet of the present population was assigned a high average score in this category for adequate intakes of proteins, iron and vitamin C but a low score for intake of vegetables. Previously, Mariscal-Arcas et al. [3] observed a high score for intake of protein, iron but also calcium, and a low score for intake of fruit, vegetables, grain and fibre among children and adolescents in southern Spain.

Moderation. In agreement with adult Balearic Islands’ population [4], adolescents’ diet is characterized by lack of moderation and it is highly unbalanced. Scores obtained for moderation in total fat and saturated fat consumption were very poor [3,4]. The DQI-I establishes moderate fat consumption as <30% of total energy, lower than the percentage found in the Spanish diet. In fact, only 10.6% of Balearic Islands adolescents had a fat intake at or below 30% of energy intake, similar than in adults (14.5%) [4]. It is known that total fat intake in Mediterranean countries is in the range of 38-40%, and olive oil is the central elemental of Mediterraneantype diets, a key contributor to its healthy properties [36,37]. Therefore, as have been suggested previously [3,4] quality rather than the quantity of fat should be take into account in dietary evaluations and guidelines.

Overall balance. The proportionally in energy sources and fatty acid composition is also examined by overall balance category. The present population had a mean macronutrient ratio of 44:17:39 (carbohydrate:protein:fat) [38]. The proportion of adolescents with a fatty acid ratio <1.7 was similar to previous studies [3,4]. However, the 2010 nutritional objectives for the Spanish population recommended 15-20% of total EI from MUFA and ≥5% from PUFA, being olive oil the main source of unsaturated fat in the Mediterranean area [39].

In the present study, the multivariate linear analysis showed that the main determinants associated with the DQI score were four: age, parental educational level, media screen time, and body image dissatisfaction. Physical activity level was also associated with the DQI score in age-adjusted linear analysis. No gender difference was observed in DQI mean score, despite the fact that girls showed higher adherence to the Mediterranean Diet than boys [40] and they were also less likely to follow a Western dietary pattern than boys [8]. The literature has also reported that girls paid more attention to foods than boys, met nutritional recommendations, and tried to prevent or reverse the obese state and improve health status [41].

Parental educational level. Parental educational level and socioeconomic status have a marked effect on children’s and adolescent’s lifestyles and dietary habits [42]. Previously, we reported that maternal educational level was associated with diet quality [14] and adherence to the Mediterranean dietary pattern among adolescents [40]. In the HELENA study, DQI was positively correlated with both parental and maternal educational level, in spite of this association was more pronounced in northern Europe than in southern Europe [35]. Contrarily to the present findings, in the HELENA study the DQI was also positively correlated with parental occupational level and this correlation was independent of the geographical area [35].

Media screen time and physical activity. Previously, we have also reported that media screen time is a good proxy for dietary pattern [8]. An association between >2 h/d watching TV and major consumption of high-fat snacks and high-sugar drinks has also been previously demonstrated [43,44]. In opposite, physical activity level has been associated with food choice, and cereals, fruits and vegetables often appear in the diet of active adult and children [45]. Children who follow a healthy diet are those who might also maintain high levels of physical activity [46]. In a previous study, we also found that sedentary and low-active adolescents showed the lowest adherence to the Mediterranean dietary pattern [40]. Therefore, it is important to note that sedentary pursuits are related to diet quality.

Body image dissatisfaction. Our results also suggest that is self-perception rather than body composition that is more closely related to diet quality. In fact, body image has been found to be a powerful determinant of adolescent nutritional habits and food choices [47]. Therefore, understanding how satisfaction with current body shape affects the food preferences and overall adolescent diet is a key issue for the development of strategies aimed at influencing dietary behavior.

Limitations of the study

The present study has several limitations. Firstly, dietary and physical activity data were based on self-reports; however, in many cases, self-reporting is the only feasible method of assessing dietary intake in epidemiological studies. Although epidemiologists made every effort to get as accurate data as possible, there is a possibility that mis-reporting occurred [48]. Secondly, nutrient intake was assessed by two non-consecutive 24 h recalls as in a previous European study performed on 1135 and 633 participants (aged 12.5-17.5 years) from northern and southern Europe, respectively [35]. Thirdly, different revised DQIs have been recently published [3,49], making comparisons between them difficult. Fourthly, body fat was calculated using Slaughter et al.’s equations [25] that have been suggested previously by Rodríguez et al. [26]. However, the present study did not take into account pubertal development despite that chronological age may vary dramatically during this phase. Therefore, as in a previous study [50] in which adolescents have been classified according to their pubertal stage, boys were divided into two groups: pubertal (12 to 14 years old) and post-pubertal (15 to 17 years old).

Conclusions

The assessed Mediterranean adolescents showed a poor-quality diet. While parental educational level and physical activity level were directly associated with diet quality, age and media screen time were inversely associated with diet quality. Body image is also a powerful determinant of adolescent diet quality. Adolescents constitute priority targets for action and should be more aware about the diet quality and its health benefits. Programs to promote the traditional Mediterranean dietary pattern among adolescents and their relatives, combined with active lifestyle, would likely result in a more favorable future health profile.

Acknowledgements

Funding: Spanish Ministry of Health and Consumption Affairs (Projects 05/1276, 08/1259, 11/01791, 14/00636, Red Predimed- RETIC RD06/0045/1004, and CIBEROBN CB12/03/30038), Grant of support to research groups no. 35/2011 (BI Govnt.) and EU FEDER funds.

Authors' contributions

MMB, JP and JAT conceived, designed, devised and supervised the study, MMB, JP and JAT collected and supervised the samples. MMB and JAT analyzed the data and wrote the manuscript. All authors read and approved the final manuscript.

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