Vegans are at an increased risk for certain micronutrient deficiencies, foremost of vitamin B12. Little is known about the short-term effects of dietary change to plant-based nutrition on vitamin B12 metabolism. Systemic biomarkers of vitamin B12 status, namely, serum vitamin B12 and holotranscobalamin, may respond quickly to a reduced intake of vitamin B12. To test this hypothesis, 53 healthy omnivore subjects were randomized to a controlled unsupplemented vegan diet (VD, n = 26) or meat-rich diet (MD, n = 27) for 4 weeks. Vitamin B12 status was examined by measurement of serum vitamin B12, holotranscobalamin (holo-TC), methylmalonic acid (MMA) and total plasma homocysteine (tHcy). Holo-TC decreased significantly in the VD compared to the MD group after four weeks of intervention, whereas metabolites MMA and tHcy were unaffected. Body weight remained stable in both groups. VD intervention led to a significant reduction of cholesterol intake, and adequate profiles of nutrient and micronutrient status. Lower intake of vitamin B12 was observed in VD, which was mirrored by a lower concentration of serum vitamin B12 and reduced holo-TC after 4 weeks. Plasma holo-TC may be a fast-responding biomarker to monitor adequate supply of vitamin B12 in plant-based individuals.

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Background Vegan diet (VD) is reported to show beneficial health effects including cardiovascular and anti-inflammatory protection, but the underlying mechanisms remain unclear. We hypothesized that adipokines, a special type of cytokine produced by the white adipose tissue with known effects on metabolism and the immune system, may contribute to the observed anti-inflammatory effects of VD. Methods A parallel group interventional trial was designed to evaluate the effect of VD compared to meat-rich diet (MD) on serum levels of two central adipokines, leptin and adiponectin. Fifty-three healthy, omnivore participants (62% female, average age 31 years and BMI 23.1 kg/m2) were randomly assigned to VD or MD for 4 weeks. Results End value comparison between VD group and MD group showed a significantly lower level of adiponectin in the MD group (11.6 vs. 15.5 µg/mL, p = 0.025) indicating a moderate effect size (Cohen’s d = 0.524). Participants’ sex affected adipokine levels requiring a separate analysis of male and female participants. Leptin was increased by MD only in male participants (p = 0.019) whereas adiponectin remained stable. Female participants in VD group showed higher adiponectin levels at the end of trial (compared to VD-baseline, p = 0.023, as well as compared to MD group, p = 0.015). The end concentration of adiponectin depended on diet in female participants (p = 0.010). Conclusion The results of our trial suggest that plasma concentration of leptin and adiponectin do not explain the immunomodulatory potential of VD in healthy participants, but it appears that diet modifies adipokine levels in a sex-specific manner.Trial registration: German Clinical Trial register (DRKS00011963), registered 30 March 2017, https://www.drks.de/drks_web/navigate.do?navigationId=trial.HTML&TRIAL_ID=DRKS00011963.