Study design and study population
The dietary surveys, EsKiMo I and II, are cross-sectional surveys, performed by the Robert Koch Institute (RKI) as part of KiGGS (Fig. 1) and funded by the BMEL. KiGGS is a nationwide representative survey on the health of children and adolescents and is part of the health monitoring system in Germany and includes three waves by now. The KiGGS baseline survey, conducted between 2003 and 2006, examined children and adolescents aged 0 to 17 years. Study design and details of the population sampling of the KiGGS baseline survey have been described elsewhere [23]. KiGGS Wave 1, the first follow-up study, was conducted as a telephone interview among participants of KiGGS baseline after about 6 years (2009–2012), also with newly invited participants aged 0–6 years [24]. Data of the second follow-up study, KiGGS Wave 2, are collected from September 2014 until August 2017 among participants of the baseline survey. In addition, a new sample of 0- to 17-year-olds is drawn, which allows cross-sectional analysis in a representative sample of this age range.
EsKiMo II is conducted within the cross sectional study population of KiGGS Wave 2. Data from about 2400 children and adolescents aged 6–17 will be collected between June 2015 and September 2017 by trained nutritionists of the RKI. Participants of EsKiMo II are a subsample of the KiGGS Wave 2 cross sectional study population who gave their consent to be contacted by further studies. All cross sectional participants who took part in the physical examination of KiGGS Wave 2, plus a random sample of cross sectional participants who only answered the KiGGS questionnaire, are invited to participate in EsKiMo II. All 167 KiGGS sample points (Fig. 2) are visited by trained nutritionists within 3 to 6 months after KiGGS Wave 2. The order of the sample point visits is precisely planned considering all German regions throughout the year to achieve a nationwide representative sample, as well as to avoid seasonal effects.
Study procedures
About four weeks before a sample point is visited, the selected children and adolescents and their parents receive an invitation letter, including a flyer with comprehensive study information, to participate in EsKiMo II. After a few days, potential participants are contacted by phone by trained interviewers, to provide more information about the background, relevance and study procedures of EsKiMo II. Upon written or oral acceptance, appointments are made within the time frame in which the sample point is visited.
A written informed consent is obtained by parents and all participants over the age of 14 years before data collection. The study is approved by Federal Commissioner for Data Protection and Freedom of Information and by the ethics committee of the Hannover Medical School (Number 2275–2015).
Home visits are performed by trained nutritionists. During these visits families with children aged 6–11 are instructed on the completion of weighted food records and adolescents aged 12–7 years are interviewed about their usual dietary intake. A short additional computer assisted interview about dietary habits is conducted for both age groups. All participants receive a monetary incentive upon their participation. In addition, they receive a personal evaluation of the reported food intake, along with corresponding nutrition information, within three months after data collection. Figure 3 gives an overview of the time schedule of the practical study procedures of EsKiMo II.
Dietary assessment
Weighted food records
Parents or legal guardians of children aged 6–11 years receive a standardized instruction by trained nutritionists at home about the completion of the weighted food. If parents or legal guardians are willing to take part in EsKiMo II but have logistical problems (such as time constraints), it is offered to conduct instructions by telephone while the required study materials are provided by post.
Parents or legal guardians of 6- to 11-years-old children have to complete two food records for their child: the first food record over three days has to be completed on predefined random selected days in the week after the home visit and a second food record over one-day should be completed on a randomly selected day between 14 and 90 days later.
For each food consumed, detailed information has to be recorded, by means of exact description of the food, including brand and product names; when applicable, fat content, particularly for milk, cheese and butter; condition at retail (e.g. frozen, conserved, fresh); preparation; kind of packaging (e.g. metal, plastic, paper); and if it is organic. Moreover, the exact time of consumption, the place of preparation, and both the weighted amount served and weighted plate wastes have to be listed. Parents or legal guardians are also asked to report the exact recipes of homemade meals. In addition, deviations from usual food intake caused by illness, celebration days or other special occasions, as well as medication and dietary supplement use, should be reported for each day. For foods consumed out of home, i.e. at schools, restaurants or while staying at friends, a separate food record is provided. It is a short, less detailed version of the weighing record, and when weighting of the amount of food consumed is not possible, portion sizes can be estimated either using a picture book of portion sizes provided or by household measures.
Supporting materials, such as a digital kitchen scale and a picture book [25, 26] for estimation of portion sizes, are provided. The 3-day-weighted food record is given to the families by the interviewer or sent per mail, if the instructions are made by telephone. The separate weighted food record is either provided directly by the interviewer (if it should be completed within the next 21 days after the instruction) or sent by mail.
Dietary history interview
Adolescents aged 12–17 years are interviewed face-to-face about their food intake within the past four weeks using the Dietary Interview Software for Health Examination Studies (DISHES). The software was developed at the RKI based on a modified dietary history method to collect data about usual dietary intakes [27]. Portion sizes can be estimated using tableware models as well as a picture book of portion sizes [25, 26]. The DISHES software was updated for EsKiMo II, integrating an actual version of the food portion database and the German Food Code and Nutrient Database Version 3.02 (BLS 3.02).
Additional questionnaire
In addition to both dietary assessment tools, a computer assisted interview is conducted with the parents or legal guardians of the 6 to 11 year olds or the adolescents themselves to assess additional information, such as in-home and in-school-meals, specific diets, and frequency of consumption of particular food groups. This also includes dietary supplement use within the last four weeks for adolescents, covering the same reference period as DISHES, or within the last 12 months for the 6–11-year-olds. If possible, pictures of the supplement packages are taken to identify the used products.
Body weight and height
Body weight and height are self-reported and inquired during the DISHES interview for adolescents and during the additional questionnaire for the 6 to 11 year olds.
Data handling
The completed food records are sent back to the RKI. Upon arrival, they are checked for completeness and plausibility, and, if necessary, inquiries are cleared by telephone. The food records are coded according to a standardized data entry manual by a trained nutritionist using the coding software EAT version 5.3, developed by the Paderborn University. After data entry, data are further handled and checked for plausibility. The amount of each food consumed is calculated as the amount served minus the amount remaining. The composition of self-prepared dishes is calculated from raw ingredients from the reported recipes.
Data from the DISHES interviews are digitally available immediately after the field phase. After some minor corrections based on notes of the interviewers during the field work, plausibility checks are applied and, when applicable, corrections are performed to the data from the DISHES interview. Plausibility checks include the identification of unusual amounts of foods consumed, i.e. extremely low or extremely high amounts, unusual table ware for foods (i.e. meat from a glass) or beverage powder without liquid.
With the consent of participants, a digital audio recording of the DISHES interview is conducted for quality assurance. These recordings are used to improve the overall data quality, since it allows verifying specific data which seem to be implausible. It is also beneficial for training purposes, interviews quality control, and the systematic recapturation of interviews, assuring standardization over time.
All reported foods are coded using the codes of the German national food composition database BLS 3.02 [28]. Throughout the field phase, information on new foods and products available on the market, which are not yet available in the BLS, is gathered in an additional food database.
For the tableware used in the DISHES interview and for the picture book, a specific food portion size database was developed with corresponding weight amounts for each reported food. The database was used in previous surveys (e. g. GeNuS and EsKiMo I [22]) and is continuously updated during the field phase of EsKiMo II.
The nutrient composition of reported supplements is collected with a supplement database made available by the Max Rubner Institute (MRI). This database was updated for EsKiMo II. The nutrient composition from all dietary supplements reported in EsKiMo II is checked with the available product information from the photographed packages, internet, other available databases, and, if available, by manufacturer information.
To further improve the representativeness of the EsKiMo II data and to correct for deviations in the population structure (e.g. age, sex, community size) between the net study sample and the German population aged 6–17 years in 2015, results will be weighted by specific weighting factors. For the food records, the weighting factor will also be corrected for unbalanced days of the week.