In my video Plant-Based Diets for Improved Mood and Productivity, I discuss a recent systematic review and meta-analysis of dietary patterns and depression that concluded that a healthy diet pattern was “significantly associated with a reduced odds of depression.” However, out of the 21 studies the researchers were able to find in the medical literature, they were only able to find one randomized controlled trial, the study design that provides the highest level of evidence. It was the study I profiled in my Improving Mood Through Diet video, in which removing meat (including fish and poultry) and eggs improved several mood scores in just two weeks.

We’ve known those eating plant-based diets tend to have healthier mood states—less tension, anxiety, depression, anger, hostility, and fatigue—but we couldn’t tell if it was cause and effect until it was put to the test, which researchers finally did. What could account for such rapid results?

Eating a vegetarian diet gives you a better antioxidant status, which may help with depression, as I discussed in Antioxidants and Depression. Also, as I previously addressed in A Better Way to Boost Serotonin, consumption of even a single carbohydrate-rich meal can improve depression, tension, anger, confusion, sadness, fatigue, alertness, and calmness scores among patients with premenstrual syndrome. But what about long term?

Overweight men and women were randomized into two groups: one following a low-carb, high-fat diet and the other following a high-carb, low-fat diet for a year. By the end of the study, who had less depression, anxiety, anger, hostility, feelings of dejection, tension, fatigue, confusion, fewer mood disturbances, and better vigor? “The sustained improvements in mood in the LF [low-fat] group compared with the LC [low-carb] group are consistent with results from epidemiological studies showing that diets high in carbohydrate and low in fat and protein are associated with lower levels of anxiety and depression and have beneficial effects on psychological well-being.”

The overall amount of fat in the research subjects’ diet didn’t change significantly, though. But the type of fat did. Their arachidonic acid intake fell to zero. Arachidonic acid is an inflammatory omega-6 fatty acid that can adversely affect mental health via a “cascade of neuroinflammation”—that is, it may inflame your brain. High levels of arachidonic acid in the bloodstream have been associated with a greater likelihood of suicidal risk and major depressive episodes, for example. How can we stay away from the stuff? Americans are exposed to arachidonic acid primarily through chicken and eggs. So, when we remove eggs, chicken, and other meat we eliminate preformed arachidonic acid from our diet.

Although high-quality treatment studies examining diet’s impact on depression are scarce, there was the successful two-week trial discussed earlier and, even better, a twenty-two-week study. Overweight or diabetic employees of a major insurance corporation received either weekly group instruction on a whole food, plant-based diet or no diet instruction for five and one-half months. There was no portion size restriction, no calorie counting, no carb counting, and no change in exercise. No meals were provided, but the company cafeteria did start offering daily plant-based options such as lentil soup, minestrone, and bean burritos.

Participants ate no meat, eggs, dairy, oil, or junk, yet they reported greater diet satisfaction compared with the control group participants who had no diet restrictions. More participants in the plant-based intervention group reported improved digestion, increased energy, and better sleep than usual at week 22 compared with the control group. They also reported a significant improvement in physical functioning, general health, vitality, and mental health. The plant-based group beat out controls on nearly every measure.

There were also significant improvements in work productivity, thought to be due in large part to their improvements in health. What this study demonstrated is that a cholesterol-free diet is acceptable, not only in research settings but also in a typical corporate environment, improving quality of life and productivity at little cost. All we needed was a large, controlled trial for confirmation, but we didn’t have such a thing… until now.

A study of ten corporate sites across the country from San Diego, California, to Macon, Georgia, with the same set-up as before found that a plant-based nutrition program in a multi-center, corporate setting improves depression, anxiety, and productivity. Significant improvements were found in depression, anxiety, fatigue, emotional well-being, and daily functioning. “Lifestyle interventions have an increasingly apparent role in physical and mental health, and among the most effective of these is the use of plant-based diets.”

The pilot data on workplace interventions can be found in my videos Slimming the Gecko and Plant-Based Workplace Intervention.

Diet can help at home, too. See:

And, for background on the inflammatory fatty acid arachidonic acid, see my videos Inflammatory Remarks About Arachidonic Acid, Chicken, Eggs, and Inflammation, and Chicken’s Fate Is Sealed.

In health,

Michael Greger, M.D.