Michael Greger, MD March 27, 2014
Why does frequent vegetable consumption seem to cut the chances of depression by more than half?
In 2012, researchers found that eliminating animal products improved mood for two weeks. Researchers blame arachidonic acid, found mainly in chickens and eggs, for negative effects on mental health. This acid provokes the development of brain inflammation.
But the improvement in plant-based mood may also be due to the phytonutrients found in plants, which cross the blood-brain barrier in our heads. A recent review in the journal Nutritional Neuroscience suggests that eating fruits and vegetables may represent a non-invasive natural and inexpensive treatment and prevention of brain disease. But how?
To understand the latest research, we need to know the underlying biology of depression, the so-called monoamine theory of depression. This idea is that depression can arise from a chemical imbalance in the brain.
One way that the billions of nerves in our brains can communicate with each other is through the mediation of chemical signals called neurotransmitters. The two nerve cells don’t really touch – there is a physical gap between them. To bridge this gap, when one nerve wants to fire another, it releases chemicals in that gap, including three monoamines: serotonin, dopamine, and norepinephrine. These neurotransmitters then swim to another nerve to get his attention. The first nerve sucks them back up again for reuse the next time it wants to talk. It also constantly produces monoamines and enzymes, monoamine oxidases, constantly absorbs them and maintains only the right amount.
How does cocaine work? It acts as a monoamine reuptake inhibitor. It blocks the first nerve, preventing it from sucking back that trio of chemicals that are forced to constantly tap on the shoulder and constantly signal to the next cell. Amphetamine works in the same way but also increases the release of monoamines. Ecstasy works like an amphetamine, but causes a comparatively greater release of serotonin.
After a while, the next nerve may say, “That’s enough!” and suppress your receptors to turn down the volume. This is comparable to earplugs. So we have to take more and more drugs to get the same effect, and then when we don’t get them, we can feel gross because the normal transmission just doesn’t get through.
Antidepressants are thought to involve similar mechanisms. People suffering from depression have elevated levels of monoamine oxidase in the brain. It is an enzyme that breaks down neurotransmitters. If our neurotransmitter levels drop, we become depressed (or so the theory goes).
Thus, a number of different classes of drugs have been developed. Tricyclic antidepressants block the reuptake of norepinephrine and dopamine. Then there were SSRIs (Selective Serotonin Reuptake Inhibitors), like Prozac. Now we know what that means – they simply block the reuptake of serotonin. There are also drugs that simply block the reuptake of norepinephrine, or block the reuptake of dopamine, or a combination of both. But if the problem is too much monoamine oxidase, why not just block the enzyme? Make monoamine oxidase inhibitors. They did, but monoamine oxidase inhibitors are considered drugs with a bad reputation due to serious side effects that can be potentially fatal.
Now we can finally talk about the latest theory as to why fruits and vegetables can improve our mood. Depression inhibitors are found in various plants. Spices like cloves, oregano, cinnamon, nutmeg inhibit monoamine oxidase, but people don’t eat enough spices to heal their brains. Tobacco has a similar effect, and this may actually be one of the reasons for the mood boost after smoking a cigarette.
Okay, but what if we don’t want to trade bad moods for lung cancer? The monoamine oxidase inhibitor found in apples, berries, grapes, cabbage, onions, and green tea can actually affect our brain biology enough to improve our mood, and it could help explain why those who prefer plant-based diets tend to have a higher mental health score.
Their other natural remedies for mental illness can recommend saffron and lavender.