What you eat impacts your mood and a study published in the October 2015 issue of the journal "Nutritional Neuroscience" found that there was a very strong correlation between vegetarian and vegan diets and an overall happier mood with less stress, anxiety and depression.

The findings, which are not conclusive, are the opposite of previous findings, which found greater feelings of stress, anxiety and depression in herbivores.

Study Methodology

The new study pulled participants from diet-related social networks on the Internet. Participants willingly agreed to answer questions relating to their diet and their mood. The study polled adult vegetarians, vegans and omnivores of all genders, across a wide geographic area.

Study participants were given a Depression, Anxiety and Stress Scale-21 (DASS-21) test, which asks questions relating to the participant's mood over the week prior to taking the survey.

Participants have the option of answering "Did not apply to me at all," applied to me some of the time," "applied to me a good part of the time" or "applied to me most of the time" to questions.

Questions on the DASS-21 ask about both physical symptoms, such as trembling or getting to sleep easily and psychological symptoms, such as feelings of unworthiness or agitation. Lower scores indicate less depression, anxiety and stress.

Study Findings

Based on participants' DASS-21 scores, both vegans and vegetarians reported less depression than omnivores. Average anxiety scores were lower in male participants only, particularly those who reported a higher fruit and vegetable intake. Lower stress scores were found in female participants only, relating to a plant-based diet and a reduction of sugar-based sweets.

A Need for More Research

While this study indicates that there doesn't seem to be any negative impact from a plant-based diet and that it could even possibly improve mood, the results are inconsistent with previous studies on the subject, which found higher stress and anxiety levels among vegetarians and vegans.

The difference could be due to a number of factors, including sample selection, selection-bias, sample size, methodological differences or the fact that all of the studies on the subject thus far have required participants to self-rank and self-report their state of mind.

While the study in "Nutritional Neuroscience" took age and gender into account when analyzing the findings of the research, they did not factor in socioeconomic status, race, education or any of the other factors that could have influenced the results one way or the other. Easy access to food from both an economic standpoint and geographic standpoint, for example, could easily lead to lower stress levels.

Because this study flies in the face of previous findings within the scientific community, more research is necessary to draw a conclusion as to whether vegetarians or vegans truly are happier than their omnivorous counterparts. As the study authors themselves said, there doesn't appear to be any inherent harm in a plant-based diet.

A Biological Basis for Benefits?

It's unclear why a vegetarian or vegan diet might be psychologically beneficial to some, but determining why the results of various studies are so vastly different takes time and more research.

However, there may be a biological basis for the benefits of a vegan diet: the 2014 issue of the scientific journal "Nutrients" ran a study on the gut microflora of vegans compared to vegetarians and omnivores. The study found that the gut profile - the bacteria, pathogens and other microorganisms found in the stomach - were vastly different between vegans and omnivores, with only a slight difference between vegetarians and vegans.

Vegans were found to have fewer pathogenic microorganisms - the kind of microorganisms that cause inflammation and disease - in their stomachs. Vegans also had a higher abundance of protective gut microflora, the type of microorganisms that promote health and prevent disease and inflammation.

The research is a promising start to understanding how vegetarians and vegans differ from their omnivorous counterparts and why a vegetarian and vegan diet might be beneficial. The results are unclear on whether starting a therapeutic vegetarian or vegan diet would help those suffering from stomach issues.

Speculations on Mental Health Benefits of a Vegan Diet

The study in "Nutrients" looks promising when we consider it from a mental health standpoint: a large majority of the body's serotonin, the "feel good chemical" that regulates moods and happiness, is produced in our stomachs. A healthier stomach environment might very well be more hospitable to proper serotonin synthesis and storage, but again, more research is needed.

There could also be other mental health benefits to vegan and vegetarian diets that aren't biologically-based. For example, if a person adopts a vegetarian or vegan diet for ethical reasons, they naturally might feel happier knowing that they're not contributing to the demand for factory-farmed animals that may face horrible lives and even more horrible deaths.

At this point, any speculation on why a vegan or vegetarian diet is beneficial to mood is just that: speculation. As time goes on and more research is conducted, we may have solid answers on the how's and why's of the beneficial nature of vegetarian and vegan diets. Until then, keep eating your veggies: it can't hurt.