Major depression is one of the most commonly diagnosed mental illnesses. Now, everyone feels sad occasionally. A full range of emotions is part of what makes us human. Depression, however, is not just sadness. It is characterized by weeks of such symptoms as low or sad mood, diminished interest in activities that used to be pleasurable, weight gain or loss, fatigue, inappropriate guilt, difficulty concentrating, and recurrent thoughts of death.
Growing evidence indicates that positive psychological well-being seems to be associated with reduced risk of physical illness, and prospective studies that follow individuals over time have found that people starting out happier may indeed end up healthier and less likely to get sick. So mental health does appear to play a part in physical health, which is why it’s crucial that the food you eat support both your mind and your body. Common foods from leafy green vegetables to your basic garden-variety tomato may positively affect your brain chemistry and help ward off depression. In fact, even simply smelling the common spice saffron may improve your emotional state.
Studies on the emotional health and mood states of those eating plant-based diets suggest that eating less meat may not only be good for us physically, but good for us emotionally too. Researchers employed two psychological tests, the Profile of Mood States (POMS) and the Depression and Anxiety Stress Scale (DASS). POMS measures levels of depression, anger, hostility, fatigue, and confusion, while DASS gauges other negative mood states as well, including hopelessness, lack of interest, anhedonia (lack of pleasure), agitation, irritability, and impatience with other people. Subjects eating plant-based diets appeared to experience significantly fewer negative emotions than omnivores. Those eating better also reported feeling more “vigor.”
The traditional explanation of how depression works, known as the monoamine theory, proposes that the condition arises out of a chemical imbalance in the brain. The levels of an important class of neurotransmitters called monoamines, which includes serotonin and dopamine, are controlled by an enzyme called monoamine oxidase (known as MAO) that breaks down any excess monoamines. People who are depressed appear to have elevated levels of this enzyme in their brains. Thus, the theory goes, depression may be caused by abnormally low levels of monoamine neurotransmitters due to elevated levels of the neurotransmitter-munching enzyme.
Many plant foods, including apples, berries, grapes, onions, and green tea, contain phytonutrients that appear to naturally inhibit MAO, as do such spices as cloves, oregano, cinnamon, and nutmeg. This may help explain why those eating plant-rich diets have lower rates of depression. Even on a day-to-day basis, studies have shown that the more fruits and vegetables you eat, the happier, calmer, and more energetic you may feel that day—and this positivity can spill over into the next day.
Avoiding the blues is not just about eating your greens, though. There are also components in certain foods that may increase the risk of depression, such as arachidonic acid, that is blamed for potentially impairing mood by inflaming the brain. The top-five sources of this inflammation-promoting compound in the American diet are chicken, eggs, beef, pork, and fish, although chicken and eggs alone contribute more than the other top sources combined. There are data suggesting that people with higher levels of arachidonic acid in their blood may end up at significantly higher risk of suicide and episodes of major depression.