Markus Keller

Dr. Markus Keller


Research Focus & Metrics

Academic Career Length

6Years (2021-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

Representative Publications

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18 May 2021 in Nutrients
Verified
Journal Article
Open access
PDF file
UAUte Alexy
Ute Alexy
MFMorwenna Fischer
Morwenna Fischer
SWStine Weder
Stine Weder
ALAlfred Längler
Alfred Längler
Andreas MichalsenAndreas Michalsen
Andreas Michalsen
MKMarkus Keller
Markus Keller
There is a lack of data on associations between modern vegetarian and vegan diets and health among children and adolescents. The aim of the Vechi Youth Study was to cross-sectionally examine anthropometry, dietary intakes and nutritional status in a sample of 149 vegetarian, 115 vegan and 137 omnivore children and adolescents (6–18 years old, mean age: 12.7 ± 3.9 years). Group differences of dietary intake (calculated from three-day dietary records), nutrient biomarker and blood lipid concentrations were assessed using an analysis of covariance, adjusted for sex, age and other covariates. The total energy intake did not differ significantly between groups, but intake of carbohydrates was higher among vegetarians and vegans than among omnivores (p = 0.0002, respectively). The median protein intake exceeded 0.9 g/kg body weight/day in all diet groups and was lowest among vegetarians (p < 0.02). There was no significant difference of haemoglobin, vitamin B2, 25-OH vitamin D3, HDL-C and triglycerides blood concentrations between diet groups. Vegan participants had higher folate concentrations than vegetarian participants (p = 0.0053). Ferritin concentration was significantly higher in omnivores than in vegetarians (p = 0.0134) and vegans (p = 0.0404). Vegetarians had lower concentrations of holotranscobalamin (p = 0.0042) and higher concentrations of methylmalonic acid (p = 0.0253) than omnivores. Vegans had the lowest non-HDL-C and LDL-C concentrations in comparison to vegetarians (p = 0.0053 and p = 0.0041) and omnivores (p = 0.0010 and p = 0.0010). A high prevalence (>30%) of 25-OH vitamin D3 and vitamin B2 concentrations below reference values were found irrespective of the diet group. In conclusion, the Vechi Youth Study did not indicate specific nutritional risks among vegetarian and vegan children and adolescents compared to omnivores.

21 December 2022 in Nutrients
Verified
Journal Article
Open access
PDF file
SWStine Weder
Stine Weder
EZEsther H. Zerback
Esther H. Zerback
SWSina M. Wagener
Sina M. Wagener
CKChristian Koeder
Christian Koeder
MFMorwenna Fischer
Morwenna Fischer
MKMarkus Keller
Markus Keller
In regions with low selenium soil concentrations, selenium can be considered a critical nutrient for vegetarians and vegans. While the number of vegetarians and vegans is increasing in many countries, a large research gap remains in this field. For example, to date, no study seems to have assessed selenium intake in vegetarian and vegan children. Therefore, the selenium intake of 1- to 3-year-old vegetarian, vegan, and omnivorous children who participated in the cross-sectional VeChi Diet study was determined. Selenium intake was assessed based on 3-day food diaries (not including supplements) and food selenium concentrations provided by the European Food Safety Authority (EFSA). Between-group differences were assessed with analysis of covariance (ANCOVA). The median daily selenium intake was 17 µg, 19 µg, and 22 µg in vegetarian, vegan, and omnivorous children, respectively. However, only the difference between the vegan and omnivorous children was statistically significant. On average, all three groups met the harmonized average requirement (H-AR) for selenium of 17 µg/day. Nevertheless, the hypothesis that vegetarian and vegan children generally consume less selenium than omnivorous children could be confirmed, and 39% of vegetarians, 36% of vegans, and 16% of omnivores fell below the adequate intake for selenium (provided by EFSA) of 15 µg/day.

27 September 2022 in Nutrients
Verified
Journal Article
Open access
PDF file
EHEva Hohoff
Eva Hohoff
HZHelena Zahn
Helena Zahn
SWStine Weder
Stine Weder
MFMorwenna Fischer
Morwenna Fischer
ALAlfred Längler
Alfred Längler
UAUte Alexy
Ute Alexy
The aim was to analyse the total food costs and the impact of food groups on total food costs among vegetarian, vegan and omnivore children and adolescents in Germany. Based on three-day weighed dietary records of 6–18-year-old children and adolescents of the VeChi Youth Study, the total daily food costs and food group costs (both EUR/day, EUR/1000 kcal) of a vegetarian (n = 145 records), vegan (n = 110) and omnivore (n = 135) diet were calculated. Minimum retail prices of 1000 empirically selected foods reported in the dietary records were linked to individual food intakes. The group differences were analysed using ANCOVA or Kruskal-Wallis tests. Vegans had the highest energy adjusted total food costs at 2.98 EUR/1000 kcal, vegetarians the lowest at 2.52 EUR/1000 kcal. Omnivores also had significantly higher costs than vegetarians with 2.83 EUR/1000 kcal/1000 kcal (p = 0.01), but the total costs did not differ significantly between omnivores and vegans (EUR/d and EUR/1000 kcal). Compared to vegetarians, vegans had significantly higher expenditures (EUR/day) on fruit (p = 0.0003), vegetables (p = 0.006), dairy alternatives (p = 0.0003) and legumes/nuts/seeds (p = 0.0003). Expenditure on starchy foods was significantly higher in the vegetarian or vegan than in the omnivore diet (p = 0.0003). Omnivores spent a quarter of their total food costs on animal source foods (25%), which is equivalent to the sum of food costs for legumes/nuts/seeds, dairy alternatives and meat alternatives in vegans and additionally dairy in vegetarians. The VeChi Youth Study indicated that financial constraints are not necessarily a barrier to switching to a more plant-based diet.

29 April 2024 in Nutrients
Verified
Journal Article
Open access
PDF file
SGSelma Kronsteiner Gicevic
Selma Kronsteiner Gicevic
LBLeonie-Helen Bogl
Leonie-Helen Bogl
MWMaria Wakolbinger
Maria Wakolbinger
SMSandra Müller
Sandra Müller
JDJoelina Dietrich
Joelina Dietrich
Eva SchernhammerEva Schernhammer
Eva Schernhammer
Background: Plant-based diets are not inherently healthy. Similar to omnivorous diets, they may contain excessive amounts of sugar, sodium, and saturated fats, or lack diversity. Moreover, vegans might be at risk of inadequate intake of certain vitamins and minerals commonly found in foods that they avoid. We developed the VEGANScreener, a tool designed to assess the diet quality of vegans in Europe. Methods: Our approach combined best practices in developing diet quality metrics with scale development approaches and involved the following: (a) narrative literature synthesis, (b) evidence evaluation by an international panel of experts, and (c) translation of evidence into a diet screener. We employed a modified Delphi technique to gather opinions from an international expert panel. Results: Twenty-five experts in the fields of nutrition, epidemiology, preventive medicine, and diet assessment participated in the first round, and nineteen participated in the subsequent round. Initially, these experts provided feedback on a pool of 38 proposed items from the literature review. Consequently, 35 revised items, with 17 having multiple versions, were suggested for further consideration. In the second round, 29 items were retained, and any residual issues were addressed in the final consensus meeting. The ultimate screener draft encompassed 29 questions, with 17 focusing on foods and nutrients to promote, and 12 addressing foods and nutrients to limit. The screener contained 24 food-based and 5 nutrient-based questions. Conclusions: We elucidated the development process of the VEGANScreener, a novel diet quality screener for vegans. Future endeavors involve contrasting the VEGANScreener against benchmark diet assessment methodologies and nutritional biomarkers and testing its acceptance. Once validated, this instrument holds potential for deployment as a self-assessment application for vegans and as a preliminary dietary screening and counseling tool in healthcare settings.

15 May 2024 in Proceedings
Verified
Conference Paper
Open access
PDF file
LKLaureen Kuhl
Laureen Kuhl
VKVanessa Keller
Vanessa Keller
SWStine Weder
Stine Weder
UAUte Alexy
Ute Alexy
MFMorwenna Fischer
Morwenna Fischer
WGWencke Gwozdz
Wencke Gwozdz
Background and objectives: There is a lack of data on the environmental impact of children’s and adolescents’ food consumption as most studies only consider adult dietary intake and, in addition, use hypothetical diets or focus on specific food products. Hence, our aim was to assess two indicators of environmental impact of the total diet among omnivorous (OM), vegetarian (VG), and vegan (VN) children and adolescents from Germany. Methods: Greenhouse gas emissions (GHGE) and land use (LU) were calculated using 3-day weighed dietary records from 820 participants (1–18 years old) of the cross-sectional VeChi Diet Study (n = 430, 1–3 years of age, conducted 2016–2018), the VeChi Youth Study (n = 390, 6–18 years, 2017–2019), and the life cycle-analyses food-item (SHARP-Indicators) database. Group differences of indicators were analysed using analysis of covariance. Results: On average, food consumption of OM, VG, and VN diets caused GHGE of 2.6, 1.6, and 1.0 kg CO2eq/kg food and LU of 3.1, 2.0, and 1.6 m2·year/kg food, respectively. The median total daily GHGE and LU amounts differed significantly between diet groups (p < 0.001). Standardisation to energy intake per 1000 kcal (GHGE: (OM) 2.2, (VG) 1.3, (VN) 0.9 kg CO2eq/1000 kcal; LU: (OM) 2.5, (VG) 1.6, (VN) 1.3 m2·year/1000 kcal) confirmed these results. Discussion and conclusions: To the best of our knowledge, this is the first evaluation to show that even in children and adolescents, the GHGE and LU caused by an OM diet is considerably higher than the GHGE and LU on a VG or VN diet. In this way, plant-based diets performed better in terms of environmental sustainability.

17 July 2025 in Nutrients
Verified
Journal Article
Open access
PDF file
JNJosefine Nebl
Josefine Nebl
PBPauline Bruns
Pauline Bruns
MMMeike Meier
Meike Meier
FMFrank Mayer
Frank Mayer
Martin SmollichMartin Smollich
Martin Smollich
MKMarkus Keller
Markus Keller
Background/Objectives: Although there is an increasing interest among athletes in adopting plant-based diets, there is insufficient research available to determine how a vegan diet affects soccer performance. Methods: This interventional pilot study examined the effect of an 8-week vegan diet (VEG, n = 10) on nutritional status and athletic performance in semi-professional soccer players compared to controls (CON, n = 8). The study employed a controlled, non-randomized, longitudinal pilot study design during the season to compare the two groups. Results: Both groups displayed overall differences in nutrient intake, including insufficient energy and carbohydrates (t2: 46.2 [40.3–52.2] En% (VEG) vs. 37.6 [34.1–41.1] En% (CON); p = 0.036, Cohen’s d = 1.321). Notably, biochemical parameters 25(OH)D and ferritin levels fell within the normal ranges for both groups. The VEG group exhibited favorable changes in total and LDL cholesterol levels. Both groups had increased performances on the treadmill over the entire course of the study (VEG: +0.87 km/h (6.6%); CON: +0.96 km/h (7%); p > 0.05). The initial relative VO2max at t0 was comparable between the groups. Primarily due to the significant weight loss in the VEG group (−1.94 kg, p = 0.007) rather than a change in absolute VO2max values, we found an increased relative VO2max in the VEG group, which was significantly different from that of the CON group (57.0 [53.7–60.3] mL/kg/min (VEG) vs. 51.6 [48.1–55.0] mL/kg/min (CON); p = 0.041, Cohen’s d = 1.675). Conclusions: These findings suggest that a short-term vegan diet does not adversely affect training-induced performance improvements and may be suitable for semi-professional soccer players.