Markus Keller

Dr. Markus Keller


Research Focus & Metrics

Academic Career Length

17Years (2010-Present)

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

Representative Publications

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12 April 2019 in Nutrients
Verified
Journal Article
Open access
PDF file
SWStine Weder
Stine Weder
MHMorwenna Hoffmann
Morwenna Hoffmann
KBKatja Becker
Katja Becker
UAUte Alexy
Ute Alexy
MKMarkus Keller
Markus Keller
Due to the lack of current, large-scale studies examining their dietary intake and health, there are concerns about vegetarian (VG) and vegan (VN) diets in childhood. Therefore, the Vegetarian and Vegan Children Study (VeChi Diet Study) examined the energy and macronutrient intake as well as the anthropometrics of 430 VG, VN, and omnivorous (OM) children (1–3 years) in Germany. A 3-day weighed dietary record assessed dietary intake, and an online questionnaire assessed lifestyle, body weight (BW), and height. Average dietary intakes and anthropometrics were compared between groups using ANCOVA. There were no significant differences in energy intake or density and anthropometrics between the study groups. OM children had the highest adjusted median intakes of protein (OM: 2.7, VG: 2.3, VN: 2.4 g/kg BW, p < 0.0001), fat (OM: 36.0, VG: 33.5, VN: 31.2%E, p < 0.0001), and added sugars (OM: 5.3, VG: 4.5, VN: 3.8%E, p = 0.002), whereas VN children had the highest adjusted intakes of carbohydrates (OM: 50.1, VG: 54.1, VN: 56.2%E, p < 0.0001) and fiber (OM: 12.2, VG: 16.5, VN: 21.8 g/1,000 kcal, p < 0.0001). Therefore, a VG and VN diet in early childhood can provide the same amount of energy and macronutrients, leading to a normal growth in comparison to OM children.

14 April 2016 in SpringerPlus
Verified
Journal Article
Open access
PDF file
KWKatharina Wirnitzer
Katharina Wirnitzer
TSTom Seyfart
Tom Seyfart
CLClaus Leitzmann
Claus Leitzmann
MKMarkus Keller
Markus Keller
GWGerold Wirnitzer
Gerold Wirnitzer
Beat KnechtleBeat Knechtle
Beat Knechtle
Beneficial and detrimental effects of various vegetarian and vegan diets on the health status are well known. Considering the growing background numbers of vegetarians and vegans, the number of vegetarian and vegan runners is likely to rise, too. Therefore, the Nutrition and Running High Mileage (NURMI) Study was designed as a comparative study to investigate the prevalence of omnivores, vegetarians, and vegans in running events and to detect potential differences in running performance comparing these three subgroups. The NURMI Study will be conducted in three steps following a cross-sectional design. Step 1 will determine epidemiological aspects of endurance runners (any distance) using a short standardized questionnaire. Step 2 will investigate dietary habits and running history from eligible participants (capable of running a half-marathon at least) using an extended standardized questionnaire. Step 3 will collect data after a running event on finishing time and final ranking as well as a post-race rating of perceived exertion, mood status, nutrient and fluid intake during the race. Our study will provide a major contribution to overcome the lack of data on the prevalence and running performance of vegetarian and vegan runners in endurance running events. We estimate the prevalence of vegetarians and vegans participating in a running event to be less compared to the respective proportion of vegetarians and vegans to the general population. Furthermore we will validate the subject’s self-assessment of their respective diet. This comparative study may identify possible effects of dietary behavior on running performance und may detect possible differences between the respective subgroups: omnivorous, vegetarian and vegan runners. Trial registration Current controlled trials, ISRCTN73074080

25 August 2016 in European Journal of Nutrition
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Journal Article
Closed access
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Rima ObeidRima Obeid
Rima Obeid
HAHussain M. Awwad
Hussain M. Awwad
MKMarkus Keller
Markus Keller
JGJuergen Geisel
Juergen Geisel

3 November 2024 in Nutrition Bulletin
Verified
Journal Article
Open access
CKChristian Koeder
Christian Koeder
MKMarkus Keller
Markus Keller
Brazil nuts are well known for their extraordinarily high selenium content. For this reason, they are frequently recommended as a kind of natural selenium ‘supplement’, particularly for certain population groups such as vegetarians and vegans in regions with low soil selenium levels. Typically, an intake of one or two Brazil nuts per day is recommended. Brazil nuts, however, also stand out from other nuts in terms of their high (albeit highly variable) radium content. The radium isotopes Ra‐226 and Ra‐228 emit alpha‐ and beta‐radiation, with this type of radiation being particularly harmful when ingested. Consequently, it is important to consider radium levels in Brazil nuts before formulating recommendations for a long‐term, daily intake of these nuts. To date, however, no comprehensive overview of radium levels in Brazil nuts has been published. Therefore, a literature review without time or language restrictions was conducted, including unpublished original data from Germany. The literature review (including the German data) indicated mean Ra‐226 and Ra‐228 levels of 49 (range: 17–205) mBq/g and 67 (range: 12–235) mBq/g, respectively. Assuming a consistent daily intake of one or two Brazil nuts, this would result in an effective dose of ~88–220 μSv/year. This level of exposure appears to be neither clearly harmful nor clearly harmless. As increased radioactivity exposure (at least at higher doses) is associated with increased cancer risk, randomised controlled trials assessing the effect of Brazil nuts on cancer risk biomarkers are needed.

1 March 2017 in The American Journal of Clinical Nutrition
Verified
Journal Article
Closed access
ASAnne-Kathrin Siebert
Anne-Kathrin Siebert
Rima ObeidRima Obeid
Rima Obeid
SWStine Weder
Stine Weder
HAHussain M Awwad
Hussain M Awwad
ASAndreas Sputtek
Andreas Sputtek
MKMarkus Keller
Markus Keller
Background: The oral application of vitamin B-12 may prevent its deficiency if the vitamin is absorbed via the mucosal barrier.Objectives: We studied the effect of the use of a vitamin B-12-fortified toothpaste on vitamin-status markers in vegans and assessed the efficiency of markers in the identification of vitamin-augmentation status.Design: In this 12-wk, double-blinded, randomized, placebo-controlled study, 76 vegans received either a placebo (n = 34) or vitamin B-12 (n = 42) toothpaste. Sixty-six subjects (n = 30 in the placebo arm; n = 36 in the vitamin B-12 arm) completed the intervention. Serum and plasma concentrations of vitamin B-12, holotranscobalamin, total homocysteine (tHcy), and methylmalonic acid (MMA) were measured before and after the intervention.Results: Both postintervention concentrations of vitamin B-12 and holotranscobalamin and their changes over 12 wk were higher in the vitamin B-12 group (mean ± SD change: 81 ± 135 pmol/L for vitamin B-12 and 26 ± 34 pmol/L for holotranscobalamin) than in the placebo group (-27 ± 64 and -5 ± 17 pmol/L, respectively) after adjustment for baseline concentrations. Postintervention concentrations of MMA and their changes differed significantly between groups (MMA changes: -0.169 ± 0.340 compared with -0.036 ± 0.544 μmol/L in vitamin B-12 and placebo groups, respectively; P < 0.001). After adjustment for baseline tHcy, postintervention concentrations of tHcy tended to be lower (P = 0.051), and the changes in tHcy (-0.7 ± 4.4 compared with 2.0 ± 5.6 μmol/L, respectively) were greater in the vitamin B-12 group than in the placebo group. Changes in vitamin B-12 markers were more prominent in vegans who reported that they had not taken vitamin B-12 supplements.Conclusion: Vitamin B-12 that is applied to the oral cavity via toothpaste enters the circulation and corrects the vitamin B-12 markers in the blood of vegans who are at higher risk of vitamin B-12 deficiency. This trial was registered at clinicaltrials.gov as NCT02679833.

19 July 2025 in Lipids in Health and Disease
Verified
Journal Article
Open access
SWStine Weder
Stine Weder
SMSandra Müller
Sandra Müller
Christine DawczynskiChristine Dawczynski
Christine Dawczynski
MKMarkus Keller
Markus Keller
The long-chain polyunsaturated fatty acid arachidonic acid (ARA, 20:4n-6) is virtually non-existent in plant foods. Concerns have therefore been raised that a predominantly plant-based diet, i.e., a vegetarian or vegan diet, could lead to ARA deficiency. ARA is discussed as conditionally essential, particularly in early infancy and childhood. Therefore, the authors of this position paper provide an overview of the state of scientific research on ARA for Western countries, with a special focus on risk groups, e.g., pregnant and breastfeeding women, infants, and children. We discuss whether ARA is potentially essential in critical life stages and whether a plant-based diet is appropriate in relation to ARA. Preliminary recommendations are derived on the basis of the available literature: healthy adults and pregnant and lactating women are able to synthetize ARA from linoleic acid (LA, 18:2n-6) and, therefore, do not require ARA supplementation, even with plant-based diets. Owing to the importance of ARA in early childhood, infants should be breastfed or given ARA-containing formula. According to current data, it can be assumed that infants, children, and adolescents are also capable of producing sufficient amounts of ARA regardless of their diet. However, these data are sparse. Furthermore, owing to the lack of reference ranges, there are no suitable test methods for diagnosing deficiency. All in all, owing to insufficient data, these recommendations are preliminary, and further studies with risk groups are urgently needed.