2.1. Study Sample

The DONALD study is an ongoing, open cohort study conducted in Dortmund, Germany, which started to collect information on diet, growth, development and metabolism of healthy children and adolescents in 1985. Since then, 35–40 infants are newly recruited every year. Eligible are healthy German infants (i.e., infants free of diseases affecting growth and/or dietary intake), whose parents are willing to participate in a long-term study and of whom at least one has sufficient knowledge of the German language. The participants are first examined at the age of 3 months and return for three more visits in the first year, two in the second year and thereafter annually until young adulthood. In the first study years, approximately 300 participants >2 years old were also recruited. Yearly examinations include 3-day weighed dietary records, anthropometric measurements, collection of 24-h urine samples (starting at age 3–4 years), interviews on lifestyle and medical examinations. Parental examinations (anthropometric measurements, lifestyle interviews) take place every four years. Further details on the study have been described elsewhere [37,38]. The study was approved by the Ethics Committee of the University of Bonn according to the guidelines of the Declaration of Helsinki, and all examinations are performed with parental and later on, children’s written consent.

At the start of the dataset compilation for the current investigation (October 2017) 17,107 records were available from the DONALD database. Incomplete records (<3 days, n = 176) were excluded as well as records from <3 years old (n = 5618) or >18 years old (n = 421) participants and records carried out after December 2016 (n = 131). For the present evaluation, we hence analysed 10,761 complete dietary records from 1312 DONALD study participants (660 boys, 652 girls). Per participant, between one (n = 153, 11.7%) and sixteen (n = 184, 14.0%) dietary records [median (Q1; Q3): 8 (3; 13)] were available.