Across all studies, there was no evidence to support a causal relation between the consumption or avoidance of meat and any psychological outcomes. However, three studies provided evidence suggesting (contradictory) temporal relations between meat-abstention and depression and anxiety. Michalak, Zhang, and Jacobi (2012) demonstrated that the mean age at the adoption of meat-abstention (30.58âyears) was substantially older than the mean age of the onset of metal disorder (24.69âyears). These authors posited that mental disorders may lead to the adoption of a meat-less diet. The authors stated that individuals with mental disorders may âchoose a vegetarian diet as a form of safety or self-protective behaviorâ (Michalak, Zhang, and Jacobi 2012, 6) due to the perception that plant-based diets are more healthful or because individuals with mental disorders may be âmore aware of suffering of animalsâ (Michalak, Zhang, and Jacobi 2012, 2). Interestingly, these investigators also found that people with a lifetime diagnosis of psychological disorders consumed less fish and fast food. While these results conflict with previous research on fast food and mental health (Crawford et al. 2011), they support Matta et al.âs results and hypothesis that the exclusion of any food group, and especially meat and poultry, is associated with increased odds of having symptoms of psychological disorders (Matta et al. 2018).
Conversely, in their longitudinal analysis, Lavallee et al. (2019) found that meat-abstention was linked to âslight increases over timeâ (Lavallee et al. 2019, 153) in depression and anxiety in Chinese students. One important caveat when considering these disparate results on temporal relations may be differences in the factors that led to meat-abstention (e.g., religious practices, health and ethical considerations, or socio-economic status). For example, economically disadvantaged individuals who do not consume meat due to its relative cost may be at risk for ill-health for myriad reasons independent of their lack of meat consumption. Thus, future research examining temporal relations should establish clear distinctions between individuals and populations that abstain from meat consumption due to ethical, religious, and health-related perceptions, or those who do not consume meat for economic reasons.
In 2012, Beezhold and Johnston (2012) conducted a RCT in which 39 self-characterized omnivores (82% female) were assigned to one of three groups: lacto-vegetarian (i.e., avoided all animal foods except dairy), ovo-pescatarian (i.e., avoided meat and poultry but consumed fish and eggs), or omnivore (i.e., consumed meat and/âor poultry at least once daily). Their results suggested that restricting meat, fish, and poultry improved some domains of short-term mood states. As detailed in our discussion, this study had major design flaws (e.g., potential observer-expectancy effects) and errors in interpretation and communication (e.g., nonequivalent groups at baseline, failure to recognize regression to the mean).
Michael St Jules đ¸ comments on Can a Vegan Diet Be Healthy? A Literature Review