In the cross-sectional VeChi Youth Study, different dietary patterns were identified not only among omnivore children and adolescents, but also within the vegetarian and vegan diet groups. These dietary patterns were differentially associated with nutrient intake. Regardless of diet group, we observed both, more health-conscious patterns as well as less favorable patterns. The dietary patterns “Vegetables and fruits” (vegetarian and omnivore), “Meat alternatives and potatoes” (vegetarian), “Vegetables and legumes” (vegan), “Fruits and convenience food” (vegan) and “Flexitarian” (omnivore) correlated with higher micronutrient density and therefore seem more health-conscious. In contrast, the patterns “Animal foods” (vegetarian), “Refined carbohydrates” (vegan), “Meat alternatives and juices” (vegan), “Dairy products” (omnivore), “Meat and convenience food” (omnivore) and “Refined grains and juices” (omnivore) were associated with a less favorable micronutrient profile and/or lower intakes of potentially critical nutrients.

Many studies using a posteriori dietary pattern analysis found various dietary patterns among omnivore children and adolescents in Western countries [22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37]. Similar to the present study, these studies were able to identify at least one beneficial pattern considered as healthy, which was characterized by high consumption of unprocessed or minimally processed plant-based foods, such as vegetables, fruits, legumes, whole grains, or nuts [22,23,24,25, 27,28,29,30,31,32,33,34]. In addition, consistent with the VeChi Youth Study, less favorable dietary patterns were identified, that focus on energy-dense and highly processed foods, such as fast food, convenience foods, snacks, sweets or sugar sweetened beverages [23,24,25,26,27, 29, 30, 32, 34, 35].

The two predominant dietary patterns in the omnivore diet group, “Flexitarian” and “Vegetables and fruits”, were both characterized by a high intake of plant-based foods, including meat- and dairy alternatives. This suggests that plant-based dietary patterns are also common among children and adolescents classified as “omnivore”. This would be consistent with the results of several studies that found increasing popularity of flexitarian diets in European countries [2, 56, 57]. Since current research [58] as well as our results show substantial differences between flexitarians and traditional omnivores in terms of food selection, nutrient intake and nutrition status [58], a differentiation between flexitarian and traditional omnivore diets seems to be useful.

To date, a posteriori dietary patterns within vegetarian or vegan diets have only been studied among adult vegans [38, 39], but the dietary patterns in these studies show certain similarities with the vegan dietary patterns found in the VeChi Youth study. In a British study with 129 adult vegans (87% female, age 18–64 years) Gallagher et al. were able to identify four different vegan dietary patterns using PCA (based on 20 food groups), the patterns „Convenience“, „Health conscious“, „Unhealthy“ and „Traditional vegan“ [39]. In a recent Austrian study with 516 vegans (mean age (SD) 28.0 (7.7), 85% female), Haider et al. identified two dietary patterns using PCA (based on 18 food groups), a “Convenience” and a “Health-conscious” pattern [38]. The “Vegetables and legumes” pattern in the VeChi Youth study shows clear parallels with the “Traditional vegan” pattern found in British vegans [39] and the “Health Conscious” pattern in Austrian vegans [38]. All three dietary patterns focus on unprocessed plant foods, especially vegetables, fruits, and potatoes. In accordance with the VeChi Youth Study, Gallagher et al. and Haider et al. also extracted more unfavorable dietary patterns [38, 39]. In particular, the “Refined carbohydrates” pattern in the VeChi Youth study shows parallels with the unhealthier “Convenience” patterns found by Gallagher et al. [39] and Haider et al. [38], as all of these patterns are characterized by higher intake of vegan convenience foods, snacks, sweets and ultra-processed food items. These similarities between our extracted dietary patterns and the vegan dietary patterns in other studies confirm the results of our pattern analysis and show that comparable vegan dietary patterns can be found in vegan children/adolescents and adults.

Unfavorable vegan dietary patterns are associated with a lower intake of legumes, whole grains, nuts, and seeds. However, sufficient intake of these food groups is of particular importance to ensure adequate supply of potentially critical nutrients (such as protein, iron, zinc, calcium, and Vitamin B2) in a vegan diet [18, 19]. In the VeChi Youth Study, the vegan subgroup was found to have the highest overall consumption of these food groups [42]. However, our analysis showed that legumes did not occur equally in all vegan dietary patterns. Only the “Vegetables and legumes” pattern was associated with higher legume consumption, whereas the “Meat alternatives and potatoes” pattern was characterized by lower consumption. Thus, with increasing consumption of meat alternatives, legumes appear to be neglected as a protein source. Higher consumption of whole grains, nuts, and seeds did not distinguish any of the identified patterns, but the “Refined carbohydrates” and “Meat alternatives and juices” patterns were associated with lower consumption of the two food groups. More unfavorable nutrient correlations were also found for these two dietary patterns, once again highlighting the importance of these food groups in providing critical nutrients.

Many of the associations between dietary patterns and energy and nutrient intake in the VeChi Youth study can also be found in other studies with omnivore children and adolescents [22, 25, 30, 37], supporting the findings of our analysis. Across these studies a posteriori dietary patterns considered healthier were associated with a more beneficial nutrient profile [22, 25, 30, 37]. As the vegetable and fruit-rich patterns in the VeChi Youth Study, the “Health conscious” or “Traditional/health-conscious” dietary patterns identified in 3-9-year-old children [30] and 13-year-old adolescents [37] in the Avon Longitudinal Study of Parents and Children (ALSPAC), were correlated with higher energy-adjusted intakes of dietary fiber and most micronutrients [30, 37]. Ambrosini et al. [22] also found these correlations in 13-year-old adolescents in the Australian Raine study. In addition, there was an inverse association between the “Healthy” pattern and energy-adjusted saturated fat intake [22], as was also shown in all three dietary groups in the VeChi Youth study. The same correlations between the above-mentioned nutrients and the identified “Healthy” patterns were also shown by Richter et al. [25] in 12- to 17-year-old girls and boys in the EsKiMo.

Similarly to other studies, the dietary patterns in the VeChi Youth study considered as unhealthier were associated with a more unfavorable nutrient profile. The vegan pattern “Refined carbohydrates” in the VeChi Youth Study showed particularly high agreement in nutrient correlations with the unfavorable dietary patterns “Snacks/sugared drinks” in the ALSPAC [37] and “Western” in the Raine study [22]. The three patterns were similar not only in the high factor loadings for sweets, snack foods, and sugar-sweetened beverages, but also correlated with higher total sugar intake and lower intakes of protein, dietary fiber, and most micronutrients (especially magnesium, iron, and zinc) [22, 37].

Patterns with individual food groups, which are classified as unfavorable due to their high degree of processing, however, cannot be clearly classified as unhealthy. In the present work, e.g. the dietary pattern “Fruits and convenience food” was the only vegan pattern to show significant positive correlations with the intake of the critical nutrients protein, zinc and calcium. This may due to the fact, that several plant-based dairy alternatives are fortified with minerals, e.g. calcium (27). In addition, negative correlations with the intake of energy, added sugars and saturated fatty acids were observed. This underlines that vegan convenience foods or more highly processed plant-based alternative products are not to be classified as unfavorable per se, but, depending on their ingredients and nutrient enrichment, can contribute to an adequate intake of critical nutrients. With increasing consumption of meat alternatives, legumes appear to be neglected as a protein source. Thus, our results can contribute to the debate about the composition of meat- and dairy alternatives and whether they should be equated to other highly processed foods [59,60,61,62].

The strengths of the VeChi Youth Study include the detailed dietary survey using 3-day weighed dietary records, in which fortified foods as well as plant-based convenience foods and alternative products were taken into account. Another strength is the large study population of vegetarian and vegan children and adolescents, including an omnivore control group, with equal age distribution and matching sociodemographic characteristics of the three diet groups.

However, the analysis also has some limitations. Due to the above-average socioeconomic status of the study participants and the regional focus in North Rhine-Westphalia, the VeChi Youth Study is not representative and the results can therefore only be generalized to a limited extent. However, the high socioeconomic status as well as the high proportion of urban residents in the study population correspond to the known sociodemographic characteristics of vegetarians and vegans [3]. In contrast, the rather high socioeconomic status in the omnivore group is probably due to selection bias [42]. Thus, in a representative study, potentially larger differences between dietary patterns and associations with health-related outcomes would be detectable.

The sample size for the pattern analysis was relatively small, as the power calculation was carried out for a different outcome, which may also affect the representativeness of our results. Overall measure of sampling adequacy according to KMO indicated insufficient suitability of the data for PCA, however the observed patterns seem plausible for vegan, vegetarian and omnivore diets. In addition, in order to obtain reliable results in the PCA, it is recommended that the number of study participants should be at least five times as large as the number of analyzed variables (food groups) [50, 63], which we were able to fulfil in our analyses. Furthermore, Bartlett test for sphericity showed a significant result in all three diet groups (P < 0.001), which indicates the adequacy of the data for PCA. Due to the small sample size, it was not possible to perform stratified analyses in addition to stratification of the diet group and thus to determine age- or sex-specific differences in dietary patterns. Therefore, we could not rule out the possibility that different age- and sex-distributions in the diet groups may have influenced our results. However, prospective studies with omnivore populations have found consistent dietary patterns from childhood to adolescence [24, 30, 64] and very similar patterns in younger girls and boys [27, 28, 32]. In adolescents, on the other hand, different dietary patterns have been found according to sex [25, 26, 65]. The extent to which vegetarian or vegan children and adolescents show age- or sex-specific differences in their dietary patterns is not known and should therefore be investigated in future studies.

With regard to the dietary assessment, it should be mentioned that the record duration of 3 days might not be sufficient for recording the participants’ habitual diet. However, more records days are discussed to may cause a decline in the quality of information [66]. As the participants were free to choose the days of the dietary records, it cannot be ruled out that the records were also completed on uncommon, unrepresentative days, such as holidays. Moreover, the dietary records were completed on three consecutive days, but at different times of the year. It is therefore possible that seasonal differences in the participants’ diet al.so had an impact on the results.

A general limitation of PCA is subjectivity, especially when aggregating food groups, determining the number of patterns to be derived, and labelling the components [67]. The population specificity also makes the identified dietary patterns difficult to reproduce. Therefore, to increase comparability with other studies, a methodological approach analogous to that used in other studies was adopted in extracting the dietary patterns [25, 26]. Furthermore, dietary patterns extracted by PCA are only able to explain a small proportion of variance in diets [68]. In the present evaluation, the individual dietary patterns extracted based on 17, 21, and 22 food groups could each explain only 7.4–13.0% of the variance in food group intake. However, these proportions of variance are consistent with the results of other studies in children [27, 35] or adolescents [