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Nutritional status of flexitarians compared to vegans and omnivores - a cross-sectional pilot study



In the Western world, there has been a notable rise in the popularity of plant-based, meat-reduced flexitarian diets. Nevertheless, there is insufficient data on the nutritional status of individuals following this dietary pattern. The aim of this study was to investigate the intake and endogenous status of various nutrients in a healthy German adult study population consisting of flexitarians (FXs), vegans (Vs) and omnivores (OMNs).


In this cross-sectional study, dietary intake of 94 non-smoking adults (32 FXs, 33 Vs, 29 OMNs) between 25 and 45 years of age was assessed using 3-day dietary records. In addition, blood samples were collected to determine different endogenous nutrient status markers.


32%, 82% and 24% of the FXs, Vs, and OMNs respectively reported using dietary supplements. In the FXs, intake of total energy as well as macronutrients and most micronutrients were within the reference range. FXs had higher intakes of fiber, retinol-equ., ascorbic acid, folate-equ., tocopherol-equ., calcium, and magnesium compared to OMNs. However, cobalamin intake in FXs (2.12 µg/d) was below the reference (4 µg/d). Based on 4cB12, 13% of FXs showed a cobalamin undersupply [< -0.5 to -2.5] compared to 10% of OMNs, and 9% of Vs. The median 25(OH)D serum concentrations in FXs, Vs and OMNs were 46.6, 55.6, and 59.6 nmol/L. The prevalence of an insufficient/deficient vitamin-D status [< 49.9 nmol 25(OH)D/L] was highest in FXs (53%), followed by Vs (34%) and OMNs (27%). In FXs and Vs, the supplement takers had better cobalamin and vitamin-D status than non-supplement takers. Anemia and depleted iron stores were found only occasionally in all groups. In women, the prevalence of pre-latent iron deficiency and iron deficiency was highest in FXs (67%) compared to Vs (61%) and OMNs (54%).


Our findings indicated that all three diets delivered sufficient amounts of most macro- and micronutrients. However, deficiencies in cobalamin, vitamin-D, and iron status were common across all diets. Further studies are needed to investigate the nutrient supply status and health consequences of meat-reduced plant-based diets. The study was registered in the German Clinical Trial Register (number: DRKS 00019887, data: 08.01.2020).

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In recent years, plant-based diets have gained interest for a variety of reasons, including ecological, ethical and health considerations, and the number of people following these diets in the Western world has increased. Additionally to vegetarianism and veganism, a plant-based, meat-reduced flexitarian (FX) dietary pattern, characterised by a consciously reduced, “flexible” consumption of meat and meat products, is also gaining popularity [1,2,3,4]. However, up to now the term “flexitarianism” has been interpreted in different ways. Springmann and colleagues [5] define the consumption of meat and meat products ≤ 1 time per week as a FX diet, while Papier et al. [6] suggest a consumption of < 2–3 times/week meat and meat products as a FX diet. Dagevos [7] identifies a FX diet when meat is eaten occasionally without avoiding it entirely. In the present study, participants were defined as FXs if they consumed ≤ 50 g/day (equivalent to ≤ 350 g/week) of meat and meat products, which reflects the lower limits of recommendations from several different nutrition societies [8,9,10,11].

When evaluating a diet, consideration of nutrient intake and endogenous status always plays an important role. It is undisputed that a lacto-ovo-vegetarian diet, based on a wide range of foods, generally fulfils all nutritional requirements in generally in adults [12,13,14]. In contrast, a strict vegan diet can be deficient with respect to micronutrients such as cobalamin as well as calcium, iron and zinc [15,16,17]. Despite growing interest, data on the nutritional situation of FX diets are limited. For example, recent studies by Kwasniewska et al. (2023) and Dawczynski et al. (2022) compared the nutritional status of different plant-based diets (including FXs) with an omnivorous dietary pattern [18, 19]. Their results showed that the intake of several micronutrients can be deficient in FXs. Overall, however, there is currently very little data on the supply of FXs with (critical) nutrients. Groufh-Jacobsen et al. [20] found that young FXs and vegans had higher general nutritional knowledge than lacto-ovo vegetarians, pescatarians and omnivores, although food literacy was moderate across all dietary practices.

Thus, the aim of this cross-sectional pilot study was to compare the nutrient intakes of healthy young and middle-aged subjects on a FX diet with those of vegans and omnivores and evaluate the actual intakes in relation to recommended intakes. To identify potential deficiencies, endogenous concentrations of cobalamin, folate, 25(OH)D, iron and related biomarkers were monitored and evaluated. In addition, differences in concentrations of nutrient status markers depending on the intake of supplements were examined.


Study design and participants

The cross-sectional study was designed and conducted at the Institute of Food Science and Human Nutrition of Leibniz University Hannover, Germany, (hereafter referred to as the Institute) according to the guidelines of the Declaration of Helsinki. It was approved by the Ethics Committee of the Medical Association of Lower Saxony in Hannover, Germany, on the 9th of September 2019 (43/2019). All subjects gave their written informed consent for the use of the data collected prior to their participation. The study was registered in the German Clinical Trial Register under the number DRKS 00019887 (registration data: 08.01.2020). In addition, the STROBE guidelines were applied [21].

The entire study design was published recently [22]. Nutrient intake and status of selected nutrients were compared among FXs, vegans and omnivores. Interested persons were included in the study if they followed the diet for ≥ 1 year:

  • flexitarian (FX) diet, if they consumed meat and meat products ≤ 50 g/day (equivalent to ≤ 350 g/week)

  • vegan (V) diet, if they consumed no food of animal origin

  • omnivore (OMN) diet, if they consumed meat and meat products ≥ 170 g/d on average (equivalent to ≥ 1190 g/week)

Meat and meat products consumption was defined as follows: meat = red and white meat, meat products = ham, sausage, cold cuts, meatballs, meat nuggets.

Consumption limits for meat and meat products were based on [8, 10, 11] for FXs and on per capita consumption between 2011–2018 for OMNs in Germany and on the European average, respectively [23, 24]. Subjects with a consumption of meat and meat products ≥ 50 g/d ≤ 170 g/d were not included in order to achieve a clear differentiation between FXs and OMNs.

We assessed the eligibility of potential participants in several steps. First, subjects had to fulfil an online screening questionnaire. The online screening questionnaire mainly contained questions about the in- and/or exclusion criteria (e.g. age, sex, anthropometrics, health status), but also specific questions about the diet (in particular the consumption of meat and meat products, milk and milk products, eggs etc.) and how long they had been following the diet to check whether the people were suitable for the FX and OMN or the V group. Secondly, potentially suitable people were invited for a face-to-face interview. The subjects were interviewed about the amount of meat and meat products consumed. After the interview it was decided whether the subjects could be included in the study.

The aim was to create a homogeneous cohort in a narrow age range. Hence, people in the age range between 25 and 45 years were included in the study. There were two main reasons for choosing this age group: First, people who follow an FX diet are most likely to be found in this age range. Second, a high level of adherence and motivation can be expected from subjects in this age group.

Further inclusion criteria for participation were: body mass index (BMI) between 20 and 28 kg/m2, metabolically healthy and non-smoker. In contrast, acute febrile infections, metabolic or malignant diseases, diseases of the gastrointestinal tract, pregnancy or lactation, endocrine and immunologic diseases, food intolerances and drug or alcohol dependence led to exclusion. Recruited subjects were matched for age and sex within each group and across the three groups (Fig. 1). Finally, eligible participants were invited to attend an examination day at the Institute. The study was carried out between March and August 2020.

Fig. 1
figure 1

Flow chart of the study

Dietary records and questionnaire of physical activity

Prior to the examination day, participants self-recorded their dietary habits using 3-day dietary records for three consecutive days, including one weekend day. All food quantities were estimated by the participants in household measures or grams. In order to increase the accuracy, participants were instructed in how to complete the 3-day dietary records in face-to-face interview prior study begin. In addition, the blank 3-day food diaries contained detailed information on examples of portion sizes, of sharing recipes or weighing food, etc. All food records were checked for completeness, legibility, and plausibility by nutritionists of the Institute. Any discrepancies were resolved by the dietitians personally with the study participants. In addition, the participants were asked whether they used dietary supplements (yes/no). In general, intakes without supplements were reported. The validated Freiburg questionnaire was used to assess health-related physical activity [25].

Anthropometric data

On the day of the examination at the Institute, height was measured with a stadiometer (Seca GmbH & Co. KG, Hamburg, Germany). Body weight was determined digitally (Seca GmbH & Co. KG, Hamburg, Germany) to the nearest 0.1 kg (lightly dressed, without shoes). From these data, the BMI was calculated according to the standard formula, i.e., the ratio of weight and height to the square [26]. All measurements were taken by trained nutritionists of the Institute.

Biochemical markers

Blood samples were collected by a licensed physician after an overnight fast (≥ 12 h) between 06:00 a.m. and 11:00 a.m. Samples were obtained by puncture of an arm vein with multifly needles into serum monovettes (3 × 7.5 ml), serum gel monovettes (1 × 7.5 ml), and EDTA monovettes (2 × 2.5 ml) from Sarstedt, Nümbrecht, Germany. A 2.5 ml EDTA monovette was centrifuged to separate plasma from serum (10 min at 2500 g). All samples were stored below 5 °C and transported to the laboratory on the same day. The analysis of all blood parameters was performed in an accredited and certified laboratory (Institute of Clinical Chemistry, Hannover Medical School, Germany).

The cobalamin status was evaluated by serum cobalamin, holotranscobalamin (Holo-TC), methylmalonic acid (MMA), total homocysteine (tHcy), and the cobalamin indicator 4cB12. Cobalamin in serum as well as parathormone (PTH) were determined by electrochemiluminescence immunoassay (ECLIA) on Cobas® 8000, module e801, Roche Diagnostics GmbH, Mannheim, Germany. Enzyme immunoassay (ELISA) was used for Holo-TC in serum from Tecan Trading AG, Hamburg, Germany. Gas chromatography coupled to mass spectrometry (GC-MS/MS) was used to analyse MMA in serum (Agilent Technologies GmbH, Waldbronn, Germany). tHcy was determined using the Cobas® 8000, module c502, Roche diagnostics GmbH, Mannheim, Germany, enzyme cycle assay. The folate status was evaluated by serum folate concentrations, which were analyzed by ECLIA on the Cobas® 8000, module e801, Roche diagnostics GmbH, Mannheim, Germany. To calculate the cobalamin indicator 4cB12, four markers were calculated according to the following formula [27]:

$$4cB12=\mathrm{log}10 (\frac{HoloTC*B12}{MMA*tHcy})-age\, factor$$

To evaluate the vitamin D status, serum 25-hydroxyvitamin D [25(OH)D] was analyzed using chemiluminescence immunoassay (CLIA) from Liaison XL, DiaSorin GmbH, Dietzenbach, Germany.

Serum iron was assessed using a spectrophotometric method on the Cobas 8000 module c701 (Roche Diagnostics GmbH, Mannheim, Germany). Serum ferritin was measured by ECLIA and serum transferrin by immunoturbidimetric assay using Cobas 8000, module c701 (Roche Diagnostics GmbH, Mannheim, Germany). Haemoglobin (Hb) was determined by capillary electrophoresis (Sebia GmbH, Fulda, Germany). Transferrin saturation, haematocrit (Hct) and mean corpuscular volume (MCV) were calculated using standard formulas.

Reference values

The Dietary Reference Intakes (DRI) values of the German, Austrian and Swiss Nutrition Societies (D-A-CH) [28] and European Food Safety Authority (EFSA) [29] were used to evaluate nutrient intakes.

Cut-offs for cobalamin and cobalamin status-related biomarkers were applied as follows: Serum cobalamin < 150 pmol/L (deficient cobalamin status) [30], MMA > 271 mmol/L (elevated) [31, 32], Holo-TC < 35 pmol/L (deficient cobalamin status) [33], tHcy > 10 µmol/L (elevated) [34, 35]. The calculated values of the 4cB12 marker were classified into five age-adjusted categories: probable cobalamin deficiency (< -2.5), possible cobalamin deficiency (-2.5 to -1.5), low cobalamin (-1.5 to -0.5), cobalamin adequacy (-0.5 to 1.5), elevated cobalamin (> 1.5) [27].

In accordance with the recommendations from the Institute of Medicine (IOM) and the D-A-CH Nutrition Society, the cut-off for serum 25(OH)D concentrations was set at > 50 nmol/L as an indicator of adequate vitamin D status [36,37,38,39,40]. 25(OH)D concentrations > 75 nmol/L were considered as desirable in view of bone health [41]. Further cut-offs were drawn, in order to evaluate concentrations below 50 nmol/L: 25(OH)D concentrations between 25–< 50 nmol/L were classified as “insufficient” and concentrations < 25 nmol/L as “deficient” according to the classification of numerous recent publications [36,37,38].

The WHO (2015) guidelines were consulted to determine serum folate concentrations (deficient < 6.8 nmol/L) [42]. Parameters of the iron status (serum iron: pre-latent iron deficiency (< 20-14 µmol/L), deficient (< 14 µmol/L); ferritin: depleted iron stores (< 15 µg/l); transferrin saturation: Insufficient iron supply (< 16%); Hb: Anaemia (female < 12 g/dl, male < 13 g/dl); Hct: Deficiency (female < 36%, male < 39%; MCV: Iron deficiency anaemia (< 80 fl)) were set according to WHO [43].

Data analysis and statistical methods

The sample size of n = 25 per group was based on a significance level (alpha) of 0.05 and a beta of 0.8 to detect between-group differences, assuming an effect size ≥ 0.8. A minimum of 30 participants per intervention group were enrolled, considering an expected dropout rate of 15%. Statistical analyses were performed using SPSS software IBM SPSS Inc. Statistics, Chicago, Il, USA. The normal distribution of the data was tested using the Kolmogorov-Smirnov test. If the data were normally distributed, one-way analysis of variance (ANOVA) was used. If the data were not normally distributed, the Kruskal-Wallis test was used. The post hoc test with Bonferroni correction was applied for significant differences, and the Chi-square test was used to compare frequencies between the three diets. Differences between intake and reference values (100%) were determined using the one-sample t-test for normally distributed data and the Wilcoxon test for non-normally distributed data. Calculations of daily intakes of macro- and micronutrients were performed using the nutrition software PRODI 8.11 (Nutri-Science GmbH, Freiburg, Germany). Statistical significance was set up at p-values ≤ 0.05. Results are presented as median (\(\widetilde{x}\)) with interquartile range (25th and 75th percentiles).


Characterisation of the study population

A total of 94 eligible young/middle-aged subjects participated in the present study. 32 were FXs, 33 were Vs, and 29 were OMNs (Table 1). Within each group and across all three diets, sex and age were matched. However, there were differences in the duration of the diets in the different groups: OMNs maintained their diet significantly longer than Vs and FXs. FXs and Vs showed higher rates of physical activity (h/week), although the difference between Vs and OMNs was significant. In all groups, the BMI was within the normal weight range, with FXs having significantly lower values than OMNs (p = 0.003). 32% of FXs reported taking dietary supplements, compared to 82% of Vs and 24% of OMNs. Thus, FXs and OMNs were significantly less likely to use dietary supplements (p ≤ 0.001 respectively).

Table 1 Characterisation of the study population

Nutrient intake

Total energy, macronutrient, dietary fiber and alcohol intake

The recommended intakes for total energy were met by FXs, whereas Vs and OMNs were below the recommended intakes (Table 2). No group differences were found. Vs had the highest carbohydrate intakes and reached reference values, whereas FXs and OMNs were below the recommended intakes. Fat intake was highest in OMNs, who exceeded the recommended intakes, followed by FXs, who were close to the recommended values. Vs had fat intakes within the reference corridor. As expected, protein intake was highest in the OMNs, followed by the FXs and the Vs. All three diets met the population reference intakes in g/kg body weight/day for protein, although the EN% recommendations were not met, mainly because of the high fat intakes. Fiber intakes were significantly different between the three groups, with Vs having the highest intakes, followed by FXs and OMNs. Reference intakes for fiber were met only by FXs and Vs. Irrespective of gender, all diets were below the maximum tolerated alcohol intake.

Table 2 Total energy, macronutrient, dietary fiber and alcohol intake

Micronutrient intake

The D-A-CH DRIs for most micronutrients were met in all groups, although some micronutrients were consumed in significantly lower or higher amounts (Fig. 2A-C, Additional file 1). FXs significantly exceeded the DRI for ascorbic acid, thiamine, riboflavin, pyridoxine as well as folate, retinol and tocopherol equivalents. Similarly, high intakes were observed for Vs for thiamine, pyridoxine, ascorbic acid and folate, retinol and tocopherol equivalents. In contrast, none of the groups reached the DRI for cobalamin [4 µg], with Vs having the lowest cobalamin intake. The daily intake of dietary vitamin D (without supplements) was very low in the entire group with FX: 2.11 µg/d (1.20–3.21); V: 1.57 µg/d (0.85–3.33); and OMN: 1.94 µg/d (1.19–2.54). Vitamin D intakes were not compared with reference intakes because the study was conducted over several seasons with varying UV radiation and no single vitamin D intake recommendation could be used for comparison.

Fig. 2
figure 2

Micronutrient intake of vitamins and minerals based on 3-day dietary record according to the reference values [100%]

When comparing mineral intakes, FXs met the DRI for calcium [1000 mg], whereas, Vs and OMNs were below. Neither FXs nor OMNs met the recommendations for potassium [4000 mg], whereby Vs reached them. Moreover, FXs as well as OMNs exceeded the recommended values for sodium [1500 mg], while Vs showed an adequate intake. Regardless of diet and sex, zinc intake rates met recommendations. Additionally, in all three diets adequate intake for iron [10 mg] and magnesium [350 mg] was observed in men. In contrast, women met the DRI for magnesium [300 mg] in all groups, but only the V women met the DRI for iron [15 mg].

Biochemical markers

Biomarkers of cobalamin and folate status

Based on the applied markers serum cobalamin, Holo-TC and 4cB12, the cobalamin status of most participants in all three groups was low but adequate (Table 3). Only 13% of FXs, 15% of Vs, and 14% of OMNs showed deficient cobalamin concentrations [< 150 pmol/L]. Based on 4cB12 13% of FXs, 10% of OMNs, and 9% of Vs showed an undersupply in cobalamin [< -0.5 to -2.5]. However, serum cobalamin and Holo-TC concentrations were significantly lower in FXs than in Vs. Not surprisingly, comparison between SU and non-SU showed for all markers that the cobalamin status was worse in non-SU. The lowest concentrations in both markers for Vs who did not take supplements. Furthermore, the 4cB12 marker showed the least favourable cobalamin status for FXs. Despite the lowest values for FXs overall, the evaluation of Vs non-SU showed the lowest concentrations, significantly less than non-SU in OMNs and FXs. Notably, in contrast, SU in the V group showed the highest concentrations in cobalamin, Holo-TC and 4cB12 across the three diets.

Table 3 Biomarkers of cobalamin and folate status

Prevalence of elevated MMA [> 271 nmol/L] and tHcy [> 10 µmol/L] concentrations was highest in FXs, followed by OMNs and Vs. Median serum folate concentrations of all three diet groups showed a low but adequate folate supply: Only 3% of FXs, 0% of Vs, and 7% of OMNs were deficient [< 6.8 nmol/L]. As expected, Vs had significantly higher serum folate concentrations, followed by FXs and OMNs.

25(OH)D and parathormone status

The median 25(OH)D concentrations in the FX group was the lowest at 46.6 nmol/L, while Vs and OMNs had slightly higher concentrations with 55.6 nmol/L and 59.6 nmol/L, respectively (Table 4). Consequently, Vs and OMNs were above the cut-off for an adequate vitamin D status [> 50 nmol 25(OH)D/L], while FXs were below the cut-off. As a result, the prevalence of an insufficient/deficient vitamin D status [< 49.9 nmol 25(OH)D/L] was highest in FXs (53%), followed by Vs (34%) and OMNs (27%). As expected, SU showed higher concentrations of 25(OH)D than non-SU across all diet groups. However, all differences were not significant. Vs had significantly higher PTH concentrations compared to FXs (p = 0.026) and OMNs (p = 0.015), however, median PTH concentrations in all three groups were within the reference range (15–65 pg/ml) [44,45,46].

Table 4 Vitamin D and parathormone (PTH) status

Biomarkers of iron status and haematological parameters

Based on markers serum iron and transferrin saturation, many people in this cohort have a poor iron status (Table 5). As expected, males had higher ferritin concentrations than females, with males in the OMN group having the highest ferritin concentrations, followed by males in the FX and V groups (p = 0.001). Women showed the same trend, but without significance. Women tend to be more affected by iron deficiency (ferritin < 15 µg/l) and iron insufficiency (transferrin saturation < 16%) than men. However, depleted iron stores (ferritin), anaemia (Hb) and iron deficiency anaemia (MCV) were observed only in a few subjects of the three dietary groups and mainly in women. In summary, the iron status of participants in the FX and V groups was the least favourable, whereas only a few women in the OMNs group had an inadequate iron status. It should be noted that no differences were observed between the three dietary groups for any of the iron status markers (except ferritin concentration in men).

Table 5 Biomarkers of iron status and haematological parameters


Plant-based diets have gained much interest in recent years and the proportion of the population adopting a FX diet is steadily increasing. While vegetarianism and veganism have been evaluated in numerous studies and compared with omnivorous diets [12, 15, 47,48,49,50,51,52], knowledge about flexitarianism is still limited. Therefore, the aim of the present study was to investigate the intake and endogenous nutrient status of flexitarians compared to vegans and omnivores within a healthy adult study group in Germany. Most of the relevant studies have only used food records to assess macro- and micronutrient intakes, and rarely assessed state-of-the-art endogenous nutrient status markers as in the present study. Our study is therefore of a pilot nature.

In general, the entire study cohort can be classified as healthy and above average active with more than 1 h of physical activity per day in all groups. Among the FXs, 32% reported using dietary supplements, compared to 24% of the OMNs. These results are comparable to the average supplement use observed in other German study cohorts of OMN subjects [49]. In addition, 82% of the Vs reported using dietary supplements. While this may seem high, it is consistent with the results of other studies in which V participants also reported supplement use between 75 and 90% [49, 51, 53, 54]. Thus, both the activity rates and the widespread use of supplements suggest that a proportion of this study cohort leads an active lifestyle and appears to be aware of the potential risks associated with their dietary choices.

All three groups were slightly below the recommended total energy intake with no relevant differences between the diets. However, protein requirements were met in all three groups. The desirable carbohydrate intake was practically only achieved by the Vs, while carbohydrate intake in FXs was halfway between the Vs and the OMNs. A higher fat and protein intake in OMNs compared to Vs in the present study was not surprising, and has been reported previously [12, 17, 19, 48]. The high fiber intake of FXs (and Vs) were close to the recommended amounts and can be considered beneficial [55].

The participants in the FX group reached the DRI for most vitamins (thiamine, riboflavin, pyridoxine, ascorbic acid as well as folate, retinol, and tocopherol equivalents) and minerals (zinc, calcium, magnesium). However, intake rates of FXs were even higher in the majority compared to OMNs. This can be attributed to the increased intake of plant foods, which are considered good sources for these micronutrients.

As green vegetables, fruits and legumes are important sources of folate, it was expected that Vs would have the highest serum folate concentrations compared to FXs and OMNs. This is in line with previous observations [12], where higher folate concentrations in Vs compared to meat eaters were described. In the present study, only one FX woman and two OMN men had deficient folate concentrations [< 6.8 nmol/l] [56]. A significantly higher prevalence of folate deficiency was found in OMNs in comparable studies [57, 58]. As low folate concentrations are also associated with contraceptive use [59], this could not be confirmed by the present data. Overall, the folate status showed that the prevalence of folic acid deficiency was low and can be considered non-critical in the present study population.

Given that the contribution of plant foods to cobalamin is negligible, the low cobalamin status in Vs, who did not take supplements, is not surprising and has been frequently observed in previous studies [12, 47,48,49, 60,61,62,63]. Although cobalamin intake of FXs (and Vs) was less than 50% of the DRI, the markers Holo-TC and 4cB12 showed that only a few participants across all diet groups showed cobalamin deficiency, in contrast to serum cobalamin. Holo-TC and the combined marker 4cB12 are considered more valid for assessing the long-term biostatus of cobalamin status [64,65,66], as cobalamin in serum can fluctuate daily and may inadequately represent the cobalamin status in tissues [67,68,69]. The body’s own cobalamin stores can last for several years. Most subjects eating a FX diet (59%) switched from an omnivore diet only a few years ago (< 5 years). However, the prevalence of cobalamin deficiency, as measured by 4cB12, was highest in the FXs compared to the Vs and OMNs. This also explains the highest prevalence of elevated MMA and tHcy in FXs. We expected that FX participants, most of whom have been on a low meat diet for several years, would still have adequate cobalamin stores. In conclusion, our data suggest that most FX participants have depleted cobalamin stores. Another explanation could be that the FX participants have been restricting their meat intake for a longer time. In consequence, FX subjects appear to be unaware of the critical supply of cobalamin, as only a few participants reported taking supplements. Therefore, to avoid cobalamin deficiency, FXs (similar to Vs) should consider cobalamin supplementation early, as is generally recommended for a V diet.

The most common sources of calcium are milk and dairy products. The finding that FXs had a higher calcium intake than Vs was therefore expected. An adequate intake of calcium, which is particularly important for bone health, is of major concern for Vs. Similarly, lower intakes of Vs compared to OMNs have already been reported [12, 15, 49, 52]. In fact, serum calcium is strictly homeostatically regulated and not directly related to dietary intake. Hence, it is not a suitable valid indicator of calcium status [40]. Therefore, we also examined PTH concentrations. Elevated PTH concentrations may indicate an increased risk of osteoporosis. Vs showed the highest PTH concentrations, but still within reference values. However, these findings emphasize the need for Vs to choose alternative, non-animal sources of calcium (e.g. mineral water, legumes) and/or appropriate supplementation [70, 71]. It should also be noted that the presence of oxalic acid reduces absorption [72].

Adequate vitamin D status is also of particular importance for calcium metabolism, bone health, cardiovascular diseases, immune system, and cancer prevention [73,74,75]. Dietary sources usually cover up only 10% to 20% of the vitamin D requirement and therefore do not significantly influence the vitamin D status [76]. The main part of vitamin D requirements must be met by a) endogenous synthesis of the vitamin requiring sunlight exposure [73, 77], and b) the supplementation of the vitamin or fortification of foods.

As expected and found in numerous studies [17, 77,78,79], intake of vitamin D from diet without supplements was very low in all groups (FX: 2.11 µg (1.20–3.21), V: 1.57 µg (0.85–3.33); OMN: 1.94 (1.19–2.54). Since the study was conducted at different seasons of the year (March to August 2020) resulting in individually varying vitamin D requirements, no uniform DRI could be assumed. We therefore did not compare the vitamin D intake with the DRI. In the absence of endogenous synthesis, vitamin D intake recommendation is between 15 µg/d [80] and 20 µg/d by [28, 81].

In the present study, the median 25(OH)D concentration in serum was poorest in the FXs compared to Vs and OMNs. In the FXs, the prevalence of an insufficient and deficient vitamin D status was 53% compared to 34% in the Vs and 27% in the OMNs. As dietary vitamin D intake via food did not differ between the groups, the difference in vitamin D status is due to other causes. Rather, the observed 25(OH)D concentrations are strongly influenced by the intake of supplements. For the FXs and Vs, the median 25(OH)D concentrations were higher for the SU than for the non-SU, while the median 25(OH)D concentrations of the non-SU were below 50 nmol/L and thus indicate an insufficient or deficient vitamin D status.

Another reason for the differences in the vitamin D status between the three groups could be differences in self-synthesis depending on sunlight (UV-B) exposure. Intensity of UV-B radiation during the study and individual sunlight exposure of the participants are unknown. However, if we infer “duration of sunlight exposure” from “physical activity” - assuming that sports are essentially done outdoors - FXs were almost as active as Vs and significantly more active than OMNs. Nevertheless, it is not possible to explain the differences in the vitamin D status between the three groups. However, our results clearly indicate that the risk for vitamin D deficiency increases without using supplements.

For iron, men’s dietary intakes were above the DRI in all groups. In women, however, iron intakes were below the DRI for FXs and OMNs, while female Vs showed iron intakes above the DRI. Similar results with significantly higher iron intakes in vegetarians or Vs compared to OMNs have already been found in other studies [12, 49]. The reason for this could be a high consumption of iron-rich plant foods such as whole grains or legumes. However, the availability of plant iron species is significantly lower compared to haem-bound iron from meat and meat products. The simultaneous intake of food components that reduce (e.g., phytate) or increase (e.g., ascorbic acid) iron availability also plays an important role and reduces the significance of purely quantitative iron intake values. A conclusion on the iron supply can therefore only be drawn employing biomarkers of iron status and haematological parameters.

As expected, all iron status markers showed significantly better iron status in men than in women in all groups. The ferritin concentrations clearly show that the OMNs had the highest iron stores despite lower iron intake, which is primarily related to the higher availability of haem-bound iron from meat and meat products as described above. Despite the highest absolute iron intake, the Vs showed the lowest ferritin status. However, serum iron and transferrin saturation values indicate that insufficient iron intake and resulting iron deficiency occur not only in women, but also in men of all three groups. It should be noted that the number of people with an inadequate iron status in each group was very small. In consequence, the results should be treated with caution and cannot be generalised.


The study has several potential limitations. The lack of statistical significance (p > 0.05) between groups for some variables (e.g., 25(OH)D, serum iron) may be due to the relatively small sample size and power of the study. This is to be expected given the exploratory nature of the study and justifies the need for a future study with larger sample sizes that would be well powered to detect small effect sizes and/or more conclusively indicate whether or not certain measures differ between diets. As a FX diet is not clearly defined, our results cannot be extrapolated to a plant-based, meat-reduced FX diet in general. Most participants were recruited through notice boards and online communities dedicated to plant-based diets. Therefore, a particular health consciousness of some subjects cannot be excluded. However, this is a general phenomenon in nutrition studies. The assessment of nutrient intake via 3-day dietary records may be somewhat biased due to possible over- or underreporting by participants and the fact that the diet during the three days may not be representative of the subject’s usual diet. In addition, the estimation of nutrient amounts in foods and food products using software-based calculation tools is vulnerable to potential errors in nutrient composition found in food databases of the nutrient intake calculation software. For a more precise evaluation of predictors of the vitamin D status, the daily sunlight exposure and the corresponding season should have been recorded in more detail. Also, we did not accurately document the intake of supplements. The study participants only stated whether they used dietary supplements, but no detailed information on frequency, composition, and dosage of dietary supplements was collected. Finally, we have no information on the prevalence of helicobacter pylori infection or atrophic gastritis in our cohort to predict dietary malabsorption of cobalamin.


In summary, the results showed that all three diets were able to provide adequate intakes of most macro- and micronutrients. However, differences could be observed in certain aspects: FXs had higher intakes of fiber, retinol equ., ascorbic acid, folate equ., tocopherol equ., calcium, and magnesium compared to OMNs. Conversely, biomarker analysis revealed a prevalence of cobalamin and iron deficiencies for FXs. Furthermore, all three groups had a very low dietary vitamin D intake and a high prevalence of an insufficient/deficient vitamin D status. Remarkably, the Vs showed awareness of micronutrient deficiencies, with over 80% using supplements. In contrast, FXs appeared to be less aware of such deficiencies, with only about 30% using supplements. In the case of vitamin D in particular, the risk of a deficiency increases if supplements are not used, regardless of the diet.

Availability of data and materials

The datasets used and/or analyzed during the current study available from the corresponding author on reasonable request.


  1. Koch F, Heuer T, Krems C, Claupein E. Meat consumers and non-meat consumers in Germany: a characterisation based on results of the German National Nutrition Survey II. J Nutr Sci. 2019;8:e21.

    Article  PubMed  PubMed Central  Google Scholar 

  2. Wozniak H, Larpin C, de Mestral C, Guessous I, Reny JL, Stringhini S. Vegetarian, pescatarian and flexitarian diets: sociodemographic determinants and association with cardiovascular risk factors in a Swiss urban population. Br J Nutr. 2020;124(8):844–52.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  3. Malek L, Umberger WJ. Distinguishing meat reducers from unrestricted omnivores, vegetarians and vegans: a comprehensive comparison of Australian consumers. Food Qual Prefer. 2021;88:104081.

    Article  Google Scholar 

  4. Neff RA, Edwards D, Palmer A, Ramsing R, Righter A, Wolfson J. Reducing meat consumption in the USA: a nationally representative survey of attitudes and behaviours. Public Health Nutr. 2018;21(10):1835–44.

    Article  PubMed  PubMed Central  Google Scholar 

  5. Springmann M, Wiebe K, Mason-D’Croz D, Sulser TB, Rayner M, Scarborough P. Health and nutritional aspects of sustainable diet strategies and their association with environmental impacts: a global modelling analysis with country-level detail. Lancet Planet Health. 2018;2(10):e451-61.

    Article  PubMed  PubMed Central  Google Scholar 

  6. Papier K, Tong TY, Appleby PN, Bradbury KE, Fensom GK, Knuppel A, et al. Comparison of major protein-source foods and other food groups in meat-eaters and non-meat-eaters in the EPIC-Oxford cohort. Nutrients. 2019;11(4):824.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  7. Dagevos H. Finding flexitarians: current studies on meat eaters and meat reducers. Trends Food Sci Technol. 2021;114:530–9.

    Article  CAS  Google Scholar 

  8. Deutsche Gesellschaft für Ernährung e. V. 10 Regeln der DGE für eine vollwertige Ernährung überarbeitet. 2017.

  9. Willett W, Rockström J, Loken B, Springmann M, Lang T, Vermeulen S, et al. Food in the Anthropocene: the EAT–Lancet Commission on healthy diets from sustainable food systems. Lancet. 2019;393(10170):447–92.

    Article  PubMed  Google Scholar 

  10. Montagnese C, Santarpia L, Buonifacio M, Nardelli A, Caldara AR, Silvestri E, et al. European food-based dietary guidelines: a comparison and update. Nutrition. 2015;31(7):908–15.

    Article  PubMed  Google Scholar 

  11. U.S. Department of Health and Human Services and U.S. Department of Agriculture. 8th edition. 2015–2020 dietary guidelines for Americans.

  12. Schüpbach R, Wegmüller R, Berguerand C, Bui M, Herter-Aeberli I. Micronutrient status and intake in omnivores, vegetarians and vegans in Switzerland. Eur J Nutr. 2017;56(1):283–93.

    Article  PubMed  Google Scholar 

  13. Craig WJ. Nutrition concerns and health effects of vegetarian diets. Nutr Clin Pract. 2010;25(6):613–20.

    Article  PubMed  Google Scholar 

  14. Position of the American Dietetic Association and Dietitians of Canada: vegetarian diets. Can J Diet Pract Res. 2003;64(2):62–81.

  15. Neufingerl N, Eilander A. Nutrient intake and status in adults consuming plant-based diets compared to meat-eaters: a systematic review. Nutrients. 2021;14(1):29.

    Article  PubMed  PubMed Central  Google Scholar 

  16. Pawlak R, Lester SE, Babatunde T. The prevalence of cobalamin deficiency among vegetarians assessed by serum vitamin B12: a review of literature. Eur J Clin Nutr. 2014;68(5):541–8.

    Article  CAS  PubMed  Google Scholar 

  17. Davey GK, Spencer EA, Appleby PN, Allen NE, Knox KH, Key TJ. EPIC-Oxford: lifestyle characteristics and nutrient intakes in a cohort of 33 883 meat-eaters and 31 546 non-meat-eaters in the UK. Public Health Nutr. 2003;6(3):259–69.

    Article  PubMed  Google Scholar 

  18. Kwaśniewska M, Pikala M, Grygorczuk O, Waśkiewicz A, Stepaniak U, Pająk A, et al. Dietary antioxidants, quality of nutrition and cardiovascular characteristics among omnivores, flexitarians and vegetarians in Poland—the results of multicenter national representative survey WOBASZ. Antioxidants. 2023;12(2):222.

    Article  PubMed  PubMed Central  Google Scholar 

  19. Dawczynski C, Weidauer T, Richert C, Schlattmann P, Dawczynski K, Kiehntopf M. Nutrient intake and nutrition status in vegetarians and vegans in comparison to omnivores - the Nutritional Evaluation (NuEva) study. Front Nutr. 2022;9:819106.

    Article  PubMed  PubMed Central  Google Scholar 

  20. Groufh-Jacobsen S, Larsson C, Daele WV, Margerison C, Mulkerrins I, Aasland LM, et al. Food literacy and diet quality in young vegans, lacto-ovo vegetarians, pescatarians, flexitarians and omnivores. Public Health Nutr. 2023:1–26.

  21. von Elm E, Altman DG, Egger M, Pocock SJ, Gøtzsche PC, Vandenbroucke JP. The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement: guidelines for reporting observational studies. J Clin Epidemiol. 2008;61(4):344–9.

    Article  Google Scholar 

  22. Bruns A, Mueller M, Schneider I, Hahn A. Application of a modified healthy eating index (HEI-Flex) to compare the diet quality of flexitarians, vegans and omnivores in Germany. Nutrients. 2022;14(15):3038.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  23. Bundesanstalt für Landwirtschaft und Ernährung RM Kritische Infrastruktur Landwirtschaft, Bonn. Bericht zur Markt- und Versorgungslage Fleisch 2018. 2018.

  24. Agricultural output - meat consumption - OECD data. Organisation for Economic Co-operation and Development (OECD). Per capita meat consumption in the EU28.

  25. Frey I, Berg A, Grathwohl D, Keul J. Freiburger Fragebogen zur körperlichen Aktivität-Entwicklung. Prüfung und Anwendung Soz Präventivmed. 1999;44(2):55–64.

    Article  CAS  PubMed  Google Scholar 

  26. Eknoyan G. Adolphe Quetelet (1796–1874)—the average man and indices of obesity. Nephrol Dial Transplant. 2008;23(1):47–51.

    Article  PubMed  Google Scholar 

  27. Fedosov SN, Brito A, Miller JW, Green R, Allen LH. Combined indicator of vitamin B12 status: modification for missing biomarkers and folate status and recommendations for revised cut-points. Clin Chem Lab Med. 2015;53(8):1215–25.

    Article  CAS  PubMed  Google Scholar 

  28. DGE - ÖGE - SGE. D-A-C-H-Referenzwerte für die Nährstoffzufuhr. 2019.

  29. European Food Safety Authority E. 2019. Dietary reference values for the EU.

  30. de Benoist B. Conclusions of a WHO Technical Consultation on folate and vitamin B12 deficiencies. Food Nutr Bull. 2008;29:S238–44.

    Article  PubMed  Google Scholar 

  31. Herrmann W, Schorr H, Bodis M, Knapp JP, Müller A, Stein G, et al. Role of homocysteine, cystathionine and methylmalonic acid measurement for diagnosis of vitamin deficiency in high-aged subjects. Eur J Clin Invest. 2000;30(12):1083–9.

    Article  CAS  PubMed  Google Scholar 

  32. Herrmann W, Obeid R, Schorr H, Geisel J. Functional vitamin B12 deficiency and determination of holotranscobalamin in populations at risk. Clin Chem Lab Med. 2003;41(11):1478–88.

    Article  CAS  PubMed  Google Scholar 

  33. Hvas AM, Nexo E. Holotranscobalamin as a predictor of vitamin B12 status. Clin Chem Lab Med. 2003;41(11):1489–92.

    Article  CAS  PubMed  Google Scholar 

  34. Malinow MR, Bostom AG, Krauss RM. Homocyst(e)ine, diet, and cardiovascular diseases: a statement for healthcare professionals from the Nutrition Committee, American Heart Association. Circulation. 1999;99(1):178–82.

    Article  CAS  PubMed  Google Scholar 

  35. Obersby D, Chappell DC, Dunnett A, Tsiami AA. Plasma total homocysteine status of vegetarians compared with omnivores: a systematic review and meta-analysis. Br J Nutr. 2013;109(5):785–94.

    Article  CAS  PubMed  Google Scholar 

  36. Lips P, Cashman KD, Lamberg-Allardt C, Bischoff-Ferrari HA, Obermayer-Pietsch B, Bianchi ML, et al. Current vitamin D status in European and Middle East countries and strategies to prevent vitamin D deficiency: a position statement of the European Calcified Tissue Society. Eur J Endocrinol. 2019;180(4):P23-54.

    Article  CAS  PubMed  Google Scholar 

  37. Amrein K, Scherkl M, Hoffmann M, Neuwersch-Sommeregger S, Köstenberger M, Tmava Berisha A, et al. Vitamin D deficiency 2.0: an update on the current status worldwide. Eur J Clin Nutr. 2020;74(11):1498–513.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  38. Gellert S, Ströhle A, Bitterlich N, Hahn A. Higher prevalence of vitamin D deficiency in German pregnant women compared to non-pregnant women. Arch Gynecol Obstet. 2017;296(1):43–51.

    Article  CAS  PubMed  Google Scholar 

  39. Maretzke F, Bechthold A, Egert S, Ernst JB, Melo van Lent D, Pilz S, et al. Role of vitamin D in preventing and treating selected extraskeletal diseases—an umbrella review. Nutrients. 2020;12(4):969.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  40. Ross AC, Taylor CL, Yaktine AL, Del Valle HB. Institute of Medicine (US) Committee to Review Dietary Reference Intakes for Vitamin D and Calcium. Dietary reference intakes for calcium and vitamin D. Washington (DC): National Academies Press (US); 2011. (The National Academies Collection: Reports funded by National Institutes of Health).

    Google Scholar 

  41. Holick MF, Binkley NC, Bischoff-Ferrari HA, Gordon CM, Hanley DA, Heaney RP, et al. Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2011;96(7):1911–30.

    Article  CAS  PubMed  Google Scholar 

  42. World Health Organization, Department of Nutrition for Health and Development (NHD). Serum and red blood cell folate concentrations for assessing folate status in populations. 2012.

  43. World Health Organization, UNICEF, United Nations University. Iron deficiency anaemia: assessment, prevention and control: a guide for programme managers. 2001.

  44. Yalla N, Bobba G, Guo G, Stankiewicz A, Ostlund R. Parathyroid hormone reference ranges in healthy individuals classified by vitamin D status. J Endocrinol Invest. 2019;42(11):1353–60.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  45. Thomas L, Herrmann W, Obeid R. Labor und Diagnose, 10. Auflage, Release 4. 2022.

  46. Pagana KD, Pagana TJ, Pagana TN. Mosby’s® diagnostic and laboratory test reference. 15th ed. Elsevier; 2020. ISBN: 9780323675215.

  47. Nebl J, Schuchardt JP, Ströhle A, Wasserfurth P, Haufe S, Eigendorf J, et al. Micronutrient status of recreational runners with vegetarian or non-vegetarian dietary patterns. Nutrients. 2019;11(5):1146.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  48. Elorinne AL, Alfthan G, Erlund I, Kivimäki H, Paju A, Salminen I, et al. Food and nutrient intake and nutritional status of Finnish vegans and non-vegetarians. PLoS One. 2016;11(2):e0148235.

    Article  PubMed  PubMed Central  Google Scholar 

  49. Weikert C, Trefflich I, Menzel J, Obeid R, Longree A, Dierkes J, et al. Vitamin and mineral status in a vegan diet. Dtsch Arztebl Int. 2020;117(35–36):575–82.

    PubMed  PubMed Central  Google Scholar 

  50. Clarys P, Deliens T, Huybrechts I, Deriemaeker P, Vanaelst B, De Keyzer W, et al. Comparison of nutritional quality of the vegan, vegetarian, semi-vegetarian, pesco-vegetarian and omnivorous diet. Nutrients. 2014;6(3):1318–32.

    Article  PubMed  PubMed Central  Google Scholar 

  51. Kristensen NB, Madsen ML, Hansen TH, Allin KH, Hoppe C, Fagt S, et al. Intake of macro- and micronutrients in Danish vegans. Nutr J. 2015;14:115.

    Article  PubMed  PubMed Central  Google Scholar 

  52. Allès B, Baudry J, Méjean C, Touvier M, Péneau S, Hercberg S, et al. Comparison of sociodemographic and nutritional characteristics between self-reported vegetarians, vegans, and meat-eaters from the NutriNet-Santé study. Nutrients. 2017;9(9):1023.

    Article  PubMed  PubMed Central  Google Scholar 

  53. Vollmer I. Vegan diet: utilization of dietary supplements and fortified foods. An internet-based survey. Ernährungs Umschau. 2018;65(9):144–53.

    Article  Google Scholar 

  54. Kuszak AJ, Hopp DC, Williamson JS, Betz JM, Sorkin BC. Approaches by the US National Institutes of Health to support rigorous scientific research on dietary supplements and natural products. Drug Test Anal. 2016;8(3–4):413–7.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  55. Reynolds AN, Akerman A, Kumar S, Diep Pham HT, Coffey S, Mann J. Dietary fibre in hypertension and cardiovascular disease management: systematic review and meta-analyses. BMC Med. 2022;20(1):139.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  56. Institute of Medicine (US) Standing Committee on the Scientific Evaluation of Dietary Reference Intakes and its Panel on Folate, Other B Vitamins, and Choline. Dietary reference intakes for thiamin, riboflavin, niacin, vitamin B6, folate, vitamin B12, pantothenic acid, biotin, and choline. Washington (DC): National Academies Press (US); 1998. (The National Academies Collection: Reports funded by National Institutes of Health).

  57. Robert Koch-Institut. Folatversorgung in Deutschland. 2016.

  58. Pfeiffer CM, Sternberg MR, Zhang M, Fazili Z, Storandt RJ, Crider KS, et al. Folate status in the US population 20 y after the introduction of folic acid fortification. Am J Clin Nutr. 2019;110(5):1088–97.

    Article  PubMed  PubMed Central  Google Scholar 

  59. Shere M, Bapat P, Nickel C, Kapur B, Koren G. Association between use of oral contraceptives and folate status: a systematic review and meta-analysis. J Obstet Gynaecol Can. 2015;37(5):430–8.

    Article  PubMed  Google Scholar 

  60. Green R, Allen LH, Bjørke-Monsen AL, Brito A, Guéant JL, Miller JW, et al. Vitamin B12 deficiency. Nat Rev Dis Primers. 2017;3(1):1–20.

    Google Scholar 

  61. Woo KS, Kwok TCY, Celermajer DS. Vegan diet, subnormal vitamin B-12 status and cardiovascular health. Nutrients. 2014;6(8):3259–73.

    Article  PubMed  PubMed Central  Google Scholar 

  62. Marrone G, Guerriero C, Palazzetti D, Lido P, Marolla A, Di Daniele F, et al. Vegan diet health benefits in metabolic syndrome. Nutrients. 2021;13(3):817.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  63. Mądry E, Lisowska A, Grebowiec P, Walkowiak J. The impact of vegan diet on B-12 status in healthy omnivores: five-year prospective study. Acta Sci Pol Technol Aliment. 2012;11(2):209–12.

    PubMed  Google Scholar 

  64. Nexo E, Hoffmann-Lücke E. Holotranscobalamin, a marker of vitamin B-12 status: analytical aspects and clinical utility. Am J Clin Nutr. 2011;94(1):359S-365S.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  65. Fedosov SN. Biochemical markers of vitamin B12 deficiency combined in one diagnostic parameter: the age-dependence and association with cognitive function and blood hemoglobin. Clin Chim Acta. 2013;422:47–53.

    Article  CAS  PubMed  Google Scholar 

  66. Campos AJ, Risch L, Nydegger U, Wiesner J, Dyck MVV, Seger C, et al. Diagnostic characteristics of 3-parameter and 2-parameter equations for the calculation of a combined indicator of vitamin B12 status to predict cobalamin deficiency in a large mixed patient population. Clin Lab. 2020;66(10).

  67. Valente E, Scott JM, Ueland PM, Cunningham C, Casey M, Molloy AM. Diagnostic accuracy of holotranscobalamin, methylmalonic acid, serum cobalamin, and other indicators of tissue vitamin B12 status in the elderly. Clin Chem. 2011;57(6):856–63.

    Article  CAS  PubMed  Google Scholar 

  68. Hannibal L, Lysne V, Bjørke-Monsen AL, Behringer S, Grünert SC, Spiekerkoetter U, et al. Biomarkers and algorithms for the diagnosis of vitamin B12 deficiency. Front Mol Biosci. 2016;3:27.

    Article  PubMed  PubMed Central  Google Scholar 

  69. Obeid R, Herrmann W. Holotranscobalamin in laboratory diagnosis of cobalamin deficiency compared to total cobalamin and methylmalonic acid. Clin Chem Lab Med. 2007;45(12):1746–50.

    Article  CAS  PubMed  Google Scholar 

  70. Weaver CM, Alexander DD, Boushey CJ, Dawson-Hughes B, Lappe JM, LeBoff MS, et al. Calcium plus vitamin D supplementation and risk of fractures: an updated meta-analysis from the National Osteoporosis Foundation. Osteoporos Int. 2016;27(1):367–76.

    Article  CAS  PubMed  Google Scholar 

  71. Vannucci L, Fossi C, Quattrini S, Guasti L, Pampaloni B, Gronchi G, et al. Calcium intake in bone health: a focus on calcium-rich mineral waters. Nutrients. 2018;10(12):1930.

    Article  PubMed  PubMed Central  Google Scholar 

  72. Mangels AR. Bone nutrients for vegetarians. Am J Clin Nutr. 2014;100:469S-475S.

    Article  CAS  PubMed  Google Scholar 

  73. Prietl B, Treiber G, Pieber TR, Amrein K. Vitamin D and immune function. Nutrients. 2013;5(7):2502–21.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  74. Charoenngam N, Holick MF. Immunologic effects of vitamin D on human health and disease. Nutrients. 2020;12(7):2097.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  75. Souberbielle JC, Body JJ, Lappe JM, Plebani M, Shoenfeld Y, Wang TJ, et al. Vitamin D and musculoskeletal health, cardiovascular disease, autoimmunity and cancer: recommendations for clinical practice. Autoimmun Rev. 2010;9(11):709–15.

    Article  CAS  PubMed  Google Scholar 

  76. Lehmann U, Gjessing HR, Hirche F, Mueller-Belecke A, Gudbrandsen OA, Ueland PM, et al. Efficacy of fish intake on vitamin D status: a meta-analysis of randomized controlled trials12. Am J Clin Nutr. 2015;102(4):837–47.

    Article  CAS  PubMed  Google Scholar 

  77. Rabenberg M, Scheidt-Nave C, Busch MA, Rieckmann N, Hintzpeter B, Mensink GBM. Vitamin D status among adults in Germany – results from the German Health Interview and Examination Survey for Adults (DEGS1). BMC Public Health. 2015;15:641.

    Article  PubMed  PubMed Central  Google Scholar 

  78. Pilz S, März W, Cashman KD, Kiely ME, Whiting SJ, Holick MF, et al. Rationale and plan for vitamin D food fortification: a review and guidance paper. Front Endocrinol (Lausanne). 2018;9:373.

    Article  PubMed  Google Scholar 

  79. Aoun A, Maalouf J, Fahed M, El Jabbour F. When and how to diagnose and treat vitamin D deficiency in adults: a practical and clinical update. J Diet Suppl. 2020;17(3):336–54.

    Article  CAS  PubMed  Google Scholar 

  80. EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA). Dietary reference values for vitamin D. EFSA J. 2016;14(10):e04547.

    Article  Google Scholar 

  81. German Nutrition Society, Bonn, Germany. New reference values for vitamin D. Ann Nutr Metab. 2012;60(4):241–6.

    Article  Google Scholar 

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AB: Conceptualisation and study design, methodology, data acquisition, evaluation and curation, writing-original draft preparation; JN: Conceptualisation and study design; WJ: reviewing and editing; AH: Conceptualisation and study design, methodology, reviewing and editing, supervision; JPS: Data validation, methodology, writing, reviewing, and editing. All authors have read and agreed to the submitted version of the manuscript.

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Correspondence to Jan Philipp Schuchardt.

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Additional file 1.

Daily intake of vitamins and minerals.

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Bruns, A., Nebl, J., Jonas, W. et al. Nutritional status of flexitarians compared to vegans and omnivores - a cross-sectional pilot study. BMC Nutr 9, 140 (2023).

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