Tryptophan and iron are also found in plentiful amounts in plant based foods. This article does not reference any peer-reviewed research, but instead looks to be taking anecdotal cases as being evidence for a vegetarian diet increasing the risk of mental illness. You can easily still eat a very unhealthy diet while being vegetarian that could easily lead to the symptoms of mental illness from lack of awareness of getting adequate nutrition from healthy food choices.

I would want to see peer-reviewed, scientific studies that control variables before being convinced that not eating meat leads to higher incidence of mental illness. To me, the more logical explanation is that some of those who decide to go vegetarian are not educating themselves on how to properly do it. They might eliminate meat and not change anything else in their diet which could lead to nutritional deficiencies. You need to increase your protein intake from other sources once you get rid of meat, as well as being aware of other key nutrients you were getting from meat that you now need to get from plants, and implement foods that contain them.

Here are a few things that were stated in the article which I find to be rather absurd:

"Then there's tryptophan, an essential amino acid found almost exclusively in poultry."

Doing a quick google search clearly shows that this is false. There are plenty of plant based foods, or even dairy which are all vegetarian that would provide adequate tryptophan.

Link showing foods - http://www.med-health.net/Foods-High-In-Tryptophan.html

"I hear from vegetarians every day; they have this terrible depression and anxiety, and they don't understand why."

So we are going to take a statement made by one person, who we do not even know the intentions of, as being evidence for there being increased incidence of mental illness? Come on now.

If you are educated on how to correctly do a vegan/vegetarian diet, there are no risks.