Summary
This meta-analysis found that compared to “meat consumers,” “meat abstainers” had higher symptom levels of depression and anxiety. The size of this effect was comparatively small. This correlation was also found for the subgroup of vegans compared to meat consumers for depression, not anxiety. A strength of this study is the assessment of study quality and the comparison between findings of high and low quality studies, in which the higher quality studies showed a stronger correlation of meat abstention with symptoms of depression and anxiety. Furthermore the authors only included studies that distinguished clearly between meat consumers and meat abstainers to avoid errors in reporting quantities of foods. Among the limitations of this study are the missing information on potential other explanations, and differences between the two groups. It was not taken into account how long the participants already followed their non-meat diet. Since only one randomized controlled trial was included in this meta-analysis, statements about causality cannot be made. Finally, the range and average severity of symptoms is not reported (e.g., mild, moderate or severe). In conclusion the authors found higher levels of symptoms for depression and anxiety among non-meat eaters but evidence of temporal and causal connections are missing.
In this meta-analysis, we examined the quantitative relation between meat consumption or avoidance, depression, and anxiety. In June 2020, we searched five online databases for primary studies examining differences in depression and anxiety between meat abstainers and meat consumers that offered a clear (dichotomous) distinction between these groups. Twenty studies met the selection criteria representing 171,802 participants with 157,778 meat consumers and 13,259 meat abstainers. We calculated the magnitude of the effect between meat consumers and meat abstainers with bias correction (Hedges’s g effect size) where higher and positive scores reflect better outcomes for meat consumers. Meat consumption was associated with lower depression (Hedges’s g = 0.216, 95% CI [0.14 to 0.30], p < .001) and lower anxiety (g = 0.17, 95% CI [0.03 to 0.31], p = .02) compared to meat abstention. Compared to vegans, meat consumers experienced both lower depression (g = 0.26, 95% CI [0.01 to 0.51], p = .041) and anxiety (g = 0.15, 95% CI [-0.40 to 0.69], p = .598). Sex did not modify these relations. Study quality explained 58% and 76% of between-studies heterogeneity in depression and anxiety, respectively. The analysis also showed that the more rigorous the study, the more positive and consistent the relation between meat consumption and better mental health. The current body of evidence precludes causal and temporal inferences.