Plasma concentrations of the cytokines Interleucin-6 (IL-6) and Tumor Necrosis Factor (TNF) alfa, the adipokine adiponectin and the acute-phase protein c-reactive protein (CRP) (measured as high-sensitive) in plasma will be used as markers of subclinical inflammation and related to the other early metabolic syndrome and cardiovascular risk markers.

Self-reported data collected by computer-assisted questionnaire interview with the parents, either personal (month 0) or by telephone (month 3 and 6). Outcomes are the number of days, during the last two weeks, with: asthma symptoms, use of asthma-medicine, hay-fever symptoms, use of hay-fever-medicine, atopic eczema, symptoms such as sore throat or fever, and the use of pain killers or antibiotics. The number of days of absence from school due to illness, the number of days of illness during weekends and holidays, and number of visits to the doctor will also be evaluated.

Among those children with a diagnosis of Attention Deficit/Hyperactivity Disorder (ADHD) or Attention Deficit Disorder (ADD), the mean daily dose of methylphenidate (based on reported intake of drugs containing this substance) during the last two weeks will be evaluated.

Content of saturated fatty acids, monounsaturated fatty acids, polyunsaturated fatty acids, total n-3 and n-6 polyunsaturated fatty acids and the n-6:n-3 ratio in whole-blood measured as weight% relative to the weight of total fatty acids.

Reading proficiency is assessed by means of the Danish Sentence Reading test 2 having two measures: Percentage of correct sentences read within eight minutes. Reading speed - number of sentences reached.

Mathematics proficiency is assessed by means of the Danish MG test for 3rd and 4th grade. They each have one measure: Number of correct results within 45 minutes.

Student learning is assessed by means of the Danish LRS Learning Rating Scale filled out by students. The scale contains four subscales and one combined scale (sum score) adding the four subscales. The subscales cover: academic learning, social situation in school, teaching style appropriateness, and school expectations.

Student wellness is assessed by means of the Danish WRS Wellness Rating Scale filled out by students. The scale contains five subscales and one combined scale (sum score) adding the five subscales. The subscales cover: Living environment, school, school mates, family, and self concept.

Physical activity is measured using actigraphy. Outcome measures will be counts/min, time spent in sedentary, light, moderate and vigorous activities.

Questions regarding TV-watching, playing with videogames and physical activity, will help identify activity-pattern.

Sleep is measured using actigraphy with the monitor placed on the right hip for all students and on the non-dominant wrist for a sub-sample. Using a sleep diary, total sleep time and sleep efficiency will be derived from these actigraphy measurements.

In addition, at month 0, the abbreviated version of the Children's Sleep Habits Questionnaire (CSHQ) is used to identify sleep problems.

Fitness is measured using the Andersen test, which is an intermittent running test to estimate maximal oxygen uptake (mL*min-1*kg-1).

Dietary intake is measured as micro-and macronutrients as well as food groups (e.g. fish and fruit/vegetables) by means of a 7-day dietary survey, which is a web based recall record method developed especially for children. Families without internet access can use a paper version of a 7-day dietary survey. The meal time perception is measured as well.

Body weight (in kg, BMI and BMI z-score calculated on the basis of the current references from the World Health Organization (WHO)

Body composition will be determined by Dual energy X-ray Absorptiometry (DXA) scanning. The parameters included are total body Fat Free Mass Index (FFMI in kg/m2), total body Fat Mass Index (FMI in kg/m2), total body fat percentage and the ratio between android and gynoid fat mass in kg.

Leptin and ghrelin. If resources are available at the end of the study period, ghrelin will be separated in acylated and deacylated ghrelin, and both the effect of the intervention on total, acylated, deacylated and the ratio between acylated:deacylated ghrelin will be assessed. If the resources are too tight at the end of the study, only total ghrelin will be used.

Serum concentrations of 25-hydroxyvitamin D [25(OH)D] will be used as marker of vitamin D status, related to food intake and time of season.

Bone Health will be evaluated by DXA scanning (total body and spine Bone Mineral Content (BMC), Bone Mineral Density (BMD), and Bone Area (BA). Osteocalcin and serum Parathyreoideahormon (PTH) are also included as markers of bone health.

Whole-blood hemoglobin and serum ferritin will be used as measures of iron status

The following five measures from the attention test D2 will be used:

TN=Total Number of items processed E%=Percentage of errors

The Omega-3 index in whole-blood is defined as the weight percentage of eicosapentaenoicacid + the weight percentage of docosahexaenoic acid in whole-blood