The researchers administered two validated psychological questionnaires, the Profile of Mood States (POMS) and the Depression Anxiety and Stress Scales (DASS) to 39 healthy adults to assess their mental health at the start of the study, and then randomly assigned them to one of three diet groups:
- A control group, which maintained regular intake of flesh foods;
- A fish group, which eliminated meat, poultry and eggs but consumed 3-4 servings per week of seafood; and
- A vegetarian group which eliminated all meat. poultry, eggs and seafood.
After 2 weeks, the researchers found that the group assigned to the vegetarian diet improved significantly on both the DASS and POMS scales, while the fish group experienced no significant improvement.
The researchers were particularly interested in participants’ blood levels of 3 fatty acids (components of fat) that affect mental health: eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and arachidonic acid (AA), EPA and DHA, which are both long-chain omega 3 fats, are touted for their ability to decrease anxiety and depression.
Yet while the fish-eating group experienced significant increases in their EPA and DHA intakes (see chart below), their mood states were not improved. On the other hand the vegetarian group significantly reduced their EPA and DHA intakes, but their mood improved substantially.
The researchers speculated that one explanation for this unexpected result was that the AA intake of the fish eaters was essentially the same as that of the control group, while the vegetarian group reduced their intake of AA to virtually zero (no great surprise, since AA is not found in plant foods).
AA gives rise to inflammatory prostaglandins, hormone-like substances which are associated with anxiety and depression.
In another study which used a cross-sectional design (i.e. assessing the mood state of people on their habitual diets, at one point in time), the same team of researchers also found that vegetarians reported significantly less negative emotion than omnivores.
Study subjects with the highest intake of EPA, DHA and AA had the worst mental health, while those with the highest intake of the plant-derived short-chain omega 3 fat, alpha-linolenic acid, and the omega 6 fat linoleic acid, experienced better mood.
These 2 studies validate my extensive clinical experience, which is that people who adopt a healthy plant-based diet feel dramatically better within a very short period of making their dietary changes.
Considering that anti-depressants may take several weeks to take effect, have a poor efficacy rate overall, and come with some very nasty side effects (including an increased risk of suicide in the first couple of weeks of taking them), dietary change should be the first treatment option explored for all people experiencing anxiety, depression, and elevated stress levels.