Impact of an eight-week isocaloric vegan dietary intervention on hemogram parameters and lymphocyte subsets: a randomized-controlled trial

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Background Whole food plant-based diets exert anti-inflammatory properties and have been associated with clinical improvements in patients with autoimmune disorders. The underlying mechanisms remain poorly understood and functional insights into nutrient-host physiology cross-talks are urgently warranted. The present study investigated the effects of an isocaloric 8-week vegan diet (VD) intervention on whole blood count parameters and lymphoid composition in comparison to a meat-rich diet (MD). Methods We conducted a two-arm, monocentric randomized-controlled trial with healthy adults who were randomly allocated to either a MD or a VD for 8 consecutive weeks. Foods of animal origin were not permitted on the VD, whereas participants in the MD group were asked to consume at least 150 g of meat per day. Results Fifty-seven participants completed the study. At week 8, significant between-group differences were found for the white blood cell count (median (interquartile range): 5.17 (1.62) *10 3 /µL in the VD group vs. 5.39 (1.92) *10 3 /µL in the MD group, p = 0.029) and the lymphocyte count (1.80 ± 0.53 *10 3 /µL in the VD group vs. 2.06 (0.74) *10 3 /µL in the MD group, p = 0.049). This difference was driven by an increase in lymphocytes in MD group participants over the course of the study. Median change scores in platelets differed between VD and MD participants (− 21 (− 31) *10 3 /µL in the VD group vs. − 1.21 ± 28.37 *10 3 /µL in the MD group, p = 0.035) and so did the neutrophil change scores (− 0.17 (− 0.31) *10 3 /µL vs. 0.13 (0.50) *10 3 /µL, p = 0.034). Mixed models for repeated measures with a time-diet interaction as a fixed effect suggested that changes in white blood cells were driven by the diet factor alone (contrast: − 0.50 (95% CI: − 0.99–(− 0.01)), p = 0.046). Immunophenotyping results suggested significant between-group differences in CD3 + and CD8 + T-cells, and CD19 + B-cells after 8 weeks. CD19 + B-cells decreased significantly in the vegan group (214.77 ± 96.64 at baseline vs. 171.56 (102.73) cells/µL at week 8). Conclusions The present study suggests that a VD, in comparison to a MD, reduces the number of various immune cells even in healthy individuals. A VD may thus exert anti-inflammatory properties. Trial registration Registered at Deutsches Register Klinischer Studien: DRKS00031541.