Assessing the change in diet from baseline to first re-examination – results from the German National Cohort (NAKO)

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Abstract Background In the NAKO cohort, dietary assessment instruments were applied at baseline (2014–2019) and during the first re-examination (2019–2024). The aim was to assess and describe changes in dietary intake over time, and to evaluate the possible consequences of pooling dietary data from both assessment periods for NAKO participants with insufficient or missing dietary information at baseline. Methods Full dietary information in both examination waves was collected in a group of 9,035 participants recruited in the study centers in Berlin-South and Freiburg. The mean difference between the baseline and first re-examination visit was 4.8 years (SD = 0.5). For both time periods, the usual intake of food items for each participant was estimated per examination wave using the modified Multiple Source Method (MSM) that incorporated repeated 24-hour food lists (24 h-FL) and a food frequency questionnaire (FFQ), combined with external data from the German National Nutrition Survey II (NVS II). Total energy intake and macronutrient intake were derived by linking food items to the German food composition database. On the individual level, differences in intake estimates were examined and the concordance was assessed. Results Overall, the results showed a high concordance of energy and macronutrient intake estimates between both time periods (ICC ≥ 0.70 for macronutrients) and only small mean differences. On average, energy intake decreased by 56 kcal/day in males and 37 kcal/day in females. At the food group level, only small changes were observed, except for the consumption of meat and meat products, as well as milk and dairy products. In females, average meat and meat product consumption decreased from baseline to the first re-examination by 7.3 g/day and in males by 14.6 g/day; the intake of milk and dairy products decreased by about 20 g/day in both females and males. Conclusion In this NAKO sub-sample, habitual intake estimates for energy, macronutrients and most food groups were highly consistent between recruitment and first re-examination. While changes in two specific food groups were observed, overall macronutrient and energy intake remained stable over the five-year period. These findings suggest that in case of incomplete dietary data at baseline, it may be appropriate to use data from both examination waves to estimate a person’s usual dietary intake.