Nutrient adequacy and Mediterranean Diet in Spanish school children and adolescents

Abstract

Objective: To evaluate dietary habits and nutritional status of Spanish school children and adolescents, and their relationship with the Mediterranean Diet.

Design: Cross-sectional study by face-to-face interview.

Setting: Free living children and adolescents of all Spanish regions.

Subjects: A random sample of 3166 people aged 6–24 y.

Methods: Home interviews conducted by a team of 43 dietitians included 24-h recalls (a second 24-h recall in 25% of the sample) and a short frequency questionnaire to determine the quality of the Mediterranean Diet (KIDMED).

Results: The participation rate was 68%. In general, the adequacy of the Mediterranean Diet rose with increased mean intakes of the majority of vitamins and minerals and decreased percentages of inadequate intakes (<2/3 of the RNI) for calcium, magnesium, vitamin B6 and C in both sexes, and iron and vitamin A only in females.

Conclusions: This study demonstrates that the Mediterranean Diet contributes to nutritional quality, and also shows concomitant risks as the Mediterranean Diet deteriorates.

Sponsorship: Kellogg's, Foundation for the Advancement of the Mediterranean Diet.

Introduction

The Mediterranean Diet is probably one of the healthiest dietary models known today, with only a few Asian diets, such as the Japanese, being comparable. The health benefits of the Mediterranean Diet have been demonstrated in numerous studies, the most outstanding being the ‘Seven-Countries Study’ conducted by Ancel Keys (1980). The Mediterranean Diet is comprised of the following foods: olive oil, bread, wheat products, vegetables and fruits, pulses and nuts, wine, cheese and yoghurt, fish and certain meats, combined with an active lifestyle conditioned by day-to-day work and commuting.

The Mediterranean Diet used to be highly caloric and rich in vitamins and minerals derived from vegetables and fruits, wholemeal cereals and virgin olive oil and fish, which made the risk of deficient micronutrient intakes quite infrequent. This explains why inadequate intakes of the B group vitamins (B1, B2, niacin, B6, folates or B12) were rare in the Mediterranean basin, where intakes of antioxidant vitamins (vitamins E and C) and carotenes were also high. However, the changes the Mediterranean Diet have undergone with regards to the reduction of calorie consumption and expenditure, the incorporation of low nutrient dense foods (such as soft drinks, sweets, bakery products), and the food processing methods (such as refinement of flour), have contributed to a increased risk of deficient intakes for some vitamins, especially folates, vitamins A and D, as well as inadequate intakes for the rest of the vitamins, in particular among certain population groups or collectives (Serra-Majem et al, 2001b,2002).

The objective of this study was to evaluate the nutritional status of the Spanish population aged 6–24 years, with regard to compliance with the Mediterranean Diet.

Materials and methods

The methodology of the EnKid study has been described elsewhere (Serra-Majem et al, 2001a,2002).

Sample

The target population consisted of all inhabitants living in Spain aged 2–24 y, and the sample population was derived from residents aged 2–24 y registered in the Spanish official population census. The theoretical sample size was set at 5500 individuals, taking into account an anticipated 70% participation rate, which would result in a sample of approximately 3850 individuals. Calculations were made, within a 95% CI, to ascertain the level of precision for estimates of parameters most likely to be compromised (micronutrients) in each stratum, as a function of the maximum sample size that the study permitted. For the purpose of this analysis, only the population aged 6–24 y was included.

Questionnaires

Dietary questionnaires and a global questionnaire incorporating questions related to socioeconomic status, education level and lifestyle factors. The dietary questionnaire used in this analysis was: one 24-h diet recall by subject; and a second 24-h diet recall in 25% of the sample. The 24-h recalls were administered throughout the year in order to avoid the influence of seasonal variations. The questionnaires were conducted in the participant's home. To avoid bias brought on by day-to-day intake variability, the questionnaires were administered homogeneously from Monday to Sunday. In order to estimate volumes and portion sizes, the household measures found in the subjects' own homes were used. The administration of two questionnaires in a subsample allowed us to adjust intakes for random intraindividual variation.

Also, a short (16-item) questionnaire was gathered in the entire sample in order to ascertain the compliance with a Mediterranean Diet model, also described elsewhere (Serra-Majem et al, in press). Based on the given answers, the test classified individuals according to the quality of the Mediterranean Diet categorised as: High, Medium or Poor. The questionnaire is shown in Table 1.

Table 1 KIDMED test to assess the Mediterranean Diet

Fieldwork

Fieldwork was initiated on 1 May 1998 and ended on 30 April 2000. Prior to conducting the interviews, participants were sent a letter of introduction and invitation to collaborate by the study coordinators.

In total, 43 dietitians or nutritionists, who had undergone a rigorous selection, training and standardisation process, conducted home interviews. Survey data were entered by the same field staff into laptop computers, which had software specifically designed for the study. Completed interview data were periodically sent to the coordinating centres in Barcelona and Bilbao.

For children aged 6–13 y, the interviews were answered by the children themselves, with support from the caretaker responsible for his/her feeding. When it was necessary, additional information was obtained from school lunch menus, conducting telephone interviews with the food service director of the school.

Food composition table

The nutrient database software used for the study consisted of the Spanish database from Mataix et al (1998), completed with information from the French (Favier et al, 1995) and British (Holland et al, 1991) food composition tables.

Statistical analyses

Data were analysed using the statistical package SPSS for Windows version 10.0. Data from the 24-h recalls were adjusted for intraindividual variability in order to accurately estimate distribution of intakes and percentage of population groups above or below defined cutoff points (RNI) (Liu et al, 1978).

For the identification of under-reporting of food intake, we used the energy intake/basal metabolic rate (EI/BMR) ratio of less than 1.14 and classified the individual as under-reported (Goldberg et al, 1991). The Reference nutrient values utilised were those elaborated by Departamento de Nutrición (1994).

Results

A total of 3166 individuals participated in the study, which represented 68.2% of the sample. Of them, 1449 were men and 1717 women.

Table 2 shows the mean intakes of energy and nutrients by age and sex with respect to the level of compliance to the Mediterranean Diet Model (KIDMED Index). Energy intake did not change according to the KIDMED Index with the exception of male adolescents aged 15–24 y, who showed tendency towards increased levels. Consumption of fibre, calcium, iron, magnesium, potassium, phosphorus and practically all the vitamins with the exception of vitamin E, increased according to the KIDMED Index.

Table 2 Nutrient intake and adhesion to the Mediterranean Diet by age and sex

In Table 3 percentage of inadequate intakes are presented (less than two-thirds of the RNI) based on the KIDMED Index. These percentages showed declines with increasing index scores for calcium, iron (in females), magnesium, vitamin B6 (excluding males aged 6–14 y), vitamin C and A (in females).

Table 3 Percentage of inadequate intakes (<2/3 RNI*) according to Mediterranean Diet adhesion by age and sex

Discussion

The dietary patterns and nutritional profile derived from enkid data reflect the changes in feeding habits and nutritional status which have occurred in Spain. It is precisely within the child and adolescent cohorts, more than any other age group, where the characteristics of the Mediterranean Diet are unravelling (Gorgojo et al, 1999; Ortega et al, 2001; Serra-Majem, 2000; Serra-Majem et al, 2001a; Sánchez Villegas et al, 2002).

This study demonstrates the high nutritional quality of the Mediterranean Diet, which contributes to the health benefits ascribed to this dietary model. For this reason, apart from better dietary fat quality and the increased quantity of antioxidants (Visioli & Galli, 2001; Su et al, 2002; Barzi et al, 2003), we should also add the factor of enhanced nutritional adequacy. The health advantages of a diet devoid of risks for inadequate intakes vs a deficient diet have been demonstrated in multiple studies (Fairfield & Fletcher, 2002; Fletcher & Fairfield, 2002; Barringer et al, 2003). However, the presence of suboptimal levels does not necessarily mean that biochemical levels or nutrient-related functions are altered. For this reason, the inclusion of biochemical indicators should be included as part of the study design. In general, the influence of intake on biochemical indicators would be important only if differences found between groups were, apart from being significant, also found to be clinically relevant (Olmedilla & Granado, 2000).

Faced with the risk of inadequate vitamin and mineral intakes, the use of fortified foods or supplements is often recommended, if nutrition education is found to be ineffective or not possible (Darnton-Hill & Nalubola, 2002; Roberfroid, 2002). This study demonstrates that when the level of adhesion to a Mediterranean Diet model is optimal, there is a reduced risk of inadequate intakes, thus making fortification and supplementation unnecessary for almost all vitamins and minerals. Health promotion strategies should be prioritised to promote the Mediterranean Diet instead of alternatives such as fortification of supplementation (Bemelmans et al, 2000; Siero et al, 2000).

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Acknowledgements

We express our appreciation to all the Enkid team investigators; a project funded by Kellogg's España SA and Kellogg's Company, Battle Creek, USA via the Fundación Universitaria de Las Palmas de Gran Canaria and the Fundación para la Investigación Nutricional. The Enkid Study Group was composed of: Directors: LI Serra-Majem and J Aranceta Bartrina; Coordinators: L Ribas Barba and C Pérez Rodrigo; Collaborators: R García Closas; L Gorgojo Jiménez, L Jover Armengol; J Ngo de la Cruz; L Peña Quintana; A Pérez Rodrigo; B Román Viñas; G Salvador Castells. Scientific Committee: Á Ballabriga Agudo (Universidad Autónoma de Barcelona); P Cervera Ral (CESNID, U.B.); A Delgado (Universidad del País Vasco); JM Martín Moreno (Ministerio de Sanidad y Consumo, Madrid); J Mataix Verdú (Universidad de Granada); M Moya (Universidad Miguel Hernández); R. Tojo Sierra (Universidad de Santiago de Compostela). We also acknowledge additional support from: E Casals Canudas; I Palma Linares; JJ Garre López; J González García; R del Llano Ribas; RD Vera García; M Olmos Castellvell and V Martín García.

Author information

Guarantor: L Serra-Majem.

Contributors: LIS-M was involved in the study planning, data analysis and paper writing. LR was responsible for the data analysis, paper preparation and edition, and fieldwork quality control. AG contributed to write the paper. CPR also contributed to the study planning and fieldwork quality control. JA also contributed to the study planning.

Correspondence to Ll Serra-Majem.

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Serra-Majem, L., Ribas, L., García, A. et al. Nutrient adequacy and Mediterranean Diet in Spanish school children and adolescents. Eur J Clin Nutr 57, S35–S39 (2003). https://doi.org/10.1038/sj.ejcn.1601812

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Keywords

  • food consumption
  • nutrient intake
  • children
  • adolescent
  • nutrition survey
  • Mediterranean Diet
  • Spain

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