Vegetarians have about twice as many episodes of depression as meat eaters, according to a new study.
The study, based on survey data from Brazil, is consistent with earlier research that found higher rates of depression among those who give up meat. However, the new study suggests that this relationship exists regardless of dietary intake.
It may seem simple to look at the relationship between a diet and certain health problems and assume that the former causes the latter through some form of nutritional deficiency.
However, the new analysis, published in the Journal of Affective Disorders, took into account a wide range of dietary factors, including total calorie intake, protein intake, micronutrient intake and level of food processing. This suggests that the higher rates of depression among vegetarians are not caused by the nutritional content of their diet.
So what could explain the link between vegetarianism and depression? Is there some non-nutritional mechanism that causes the former to cause the latter? Or is the relationship due to something else entirely?
First, it is possible that depression makes people more likely to become vegetarians rather than the other way around. Symptoms of depression can include rumination on negative thoughts, as well as feelings of guilt.
Assuming that depressed and non-depressed individuals are equally likely to encounter the chilling truth of slaughterhouses and factory farms, it is possible that depressed individuals are more likely to ruminate on these thoughts and more likely to feel guilty about their role in creating demand .
The depressed vegetarian, in this case, is not necessarily wrong to think so. While depression is sometimes characterized as unrealistically negative perceptions, there is evidence to suggest that people with mild to moderate depression have more realistic judgments about the outcome of uncertain events and more realistic perceptions of their role and abilities.
In this case, there is really cruel treatment of animals in meat production. And this is really caused by consumer demand for cheap meat.
Second, it is possible that following a vegetarian diet causes depression for reasons other than diet. Even if no “happy nutrients” are missing from a vegetarian diet, giving up meat can cause depression by other means.
For example, adopting a vegetarian diet can affect one’s relationship with others and participation in social activities, and can sometimes be associated with teasing or other forms of social ostracism.
It’s worth noting that the new study is based on survey data collected in Brazil, a country famous for its heavy meat diet. Some survey data has shown a sharp increase in vegetarianism in Brazil in recent years, from 8% in 2012 to 16% in 2018. However, the recent survey surveyed more than 14,000 Brazilians and found just 82 vegetarians – barely more than half per cent.
One has to wonder if the same relationship between vegetarianism and depression would be seen in India or other countries where vegetarianism is more of a social norm. More importantly, as the rate of vegetarianism increases in the UK and other developed countries, will we see the relationship disappear over time?
Finally, it is possible that neither vegetarianism nor depression causes the other, but both are linked to some third factor. This could be any number of characteristics or experiences associated with both vegetarianism and depression.
For example, women are more likely than men to be vegetarians and to experience depression. However, the Brazilian study took gender into account, excluding this particular third variable.
One variable not examined, but plausibly associated with both vegetarianism and depression, is exposure to violent images of the meat industry. Preventing animal cruelty is the most commonly cited reason vegetarians give for avoiding meat.
Documentaries like Dominion and Earthlings that depict cruelty in the meat industry cannot easily be described as friendly films. One can easily imagine that a person consuming this type of media would become both a vegetarian and, especially when most people choose to look the other way, depressed.
There are several possible reasons for the link between vegetarianism and depression. This new study suggests that a vegetarian diet is not the cause of depression.
Conversely, vegetarian social experience may contribute to depression, depression may cause an increased likelihood of becoming a vegetarian, or both vegetarianism and depression may be caused by a third variable, such as exposure to violent images of the meat industry.
Chris Bryant, Honorary Research Associate, Department of Psychology, University of Bath
This article is republished from The Conversation under a Creative Commons license. Read the original article.