Vegetarian diets could be linked with higher depression scores, suggests a huge meta-analysis of almost 50,000 people by researchers in Bochum, Germany. The research backs up existing studies that have linked ditching meat to an increased likelihood of depression, but the reason why remains elusive.
Whether vegetarianism actually plays a role in depression is poorly understood. Some studies have pointed the finger at the diet, while others have refuted the findings. To identify a link – if there is one – Sebastian Ocklenburg and Jette Borawski performed a large-scale meta-analysis on published studies that compared the depression scores of non-vegetarians and vegetarians. Their results are published in the Journal of Affective Disorders.
After accounting for duplicates, there were a total of 8,057 vegetarians and 41,832 non-vegetarians included in the analysis. While the sample was large, many of the participants were from similar countries, and so the diversity within the study was relatively low.
The researchers then used a statistical program to scour the studies for mood disorder scores and sufficient data to be considered significant, and 13 studies fit the bill.
Once all the findings were analyzed, the researchers discovered a significant increase in the depression scores of vegetarians compared to non-vegetarians. However, while the data was significant, there was also significant heterogeneity in the studies (how conflicting the results were between each study), indicating there was certainly not a unanimous conclusion.
The authors are clear in their paper that they wish to make no conclusions based on the results – it is still unclear whether the link is causal from the diet, or whether those that experience depression are more likely to choose vegetarianism. In one study included in the analysis, for example, the results indicated that more often than not, people with depressive symptoms started their vegetarian diet after the onset of the disorder, suggesting it is not a causal link. It is suggested that depression may make the person more health-conscious, leading them to vegetarianism, or that depression enhances the feelings of empathy towards animals. This is purely speculation at the current time, however.
With a significant link established, the authors now call for further research to understand its true nature. The first step would be to include more countries into the studies, as there is a clear bias in many of the studies towards a small number of countries. Once these are included, identifying whether the diet underlies the symptoms, or is purely a resulting lifestyle, will be incredibly important.