Vegans abstain from all animal products, for example, meat, fish, milk and dairy products, honey and other substances from animal origin, like milk powder. Nevertheless, countless foods remain that are “vegan” by nature: vegetables, fruits, cereals, legumes, rice, nuts, pasta (if made without eggs, of course), and so on. By contrast, vegetarians eat products made of meat but don’t eat meat and fish itself [1, 2].
Positive results on (mental) health:
- A raw vegan diet brought a positive change in quality of life, and a decrease of anxiety and stress 
- A low-fat vegan diet for people with diabetes or BMI >=25 over 22 weeks showed that general health, physical functioning, mental health, and vitality improved in the vegan group 
- In the vegan group, lower stress and anxiety were observed. In men, lower anxiety was related to a vegan diet; in females, lower stress was related to the vegan diet and a lower daily intake of sweets 
- Vegans tend to be thinner, have lower serum cholesterol, and lower blood pressure, which is reducing their risk of heart disease 
- A vegetarian diet is associated with many health benefits because of its higher content of fiber, folic acid, vitamins C and E, potassium, magnesium, and many phytochemicals and fat content that is more unsaturated 
But is the only difference the food intake? 
- smoke or drink less than average
- exercise more
- care more about the ethics and quality of their food
- are less likely to eat fast food
And there are also negative results:
On the contrary, there are studies stating that a strictly vegan/vegetarian diet may be a risk factor for mental health; e.g. higher anxiety and depression levels compared to people who also ate meat and other animal products [8,9].
But this might be explained by a key bias because the majority of vegan/vegetarian eaters are female, unmarried, younger, and highly educated. These are all characteristics that are associated with a higher prevalence of mental disorders .
So, more research is needed until we can state whether a vegetarian or vegan lifestyle might be beneficial for our mental health or not. Generally speaking, enhancing the fruit, vegetable, and legume content of our everyday food will lead to increased uptake of vitamins, minerals, trace elements, and fibers. These are necessary for a physically healthy lifestyle – and most likely for your mental health status, too.