Can We Fight the Blues With Greens?

Why does frequent consumption of vegetables appear to cut one’s odds of depression by more than half? And by more frequent, I mean eating vegetables not 3 or more times a day, but just 3 or more times a week. How are plants doing that?

In a 2012 study that found eliminating animal products improved mood within two weeks, the researchers blamed arachidonic acid, found primarily in chicken and eggs, which they thought might adversely impact mental health via a cascade of brain inflammation. More on this inflammatory omega-6 fatty acid in:

But better moods on plant-based diets could also be from the good stuff in plants—a class of phytonutrients that cross the blood brain barrier into our heads. A recent review in the journal Nutritional Neuroscience suggests that eating lots of fruits and vegetables “may present a noninvasive natural and inexpensive therapeutic means to support a healthy brain.” Yeah, but how?

To understand the latest research, we need to understand the underlying biology of depression—the so-called monoamine theory. The idea is that depression may arise out of a chemical imbalance in the brain. Here’s the oversimplified version: One of the ways the billions of nerves in our brain communicate with one another is through chemical signals called neurotransmitters. If you click on the above video, you can see the end of one nerve and the beginning of another, which will help with this explanation.

Note the two nerve cells don’t actually touch—there’s a physical gap between them. To bridge that gap, when one nerve wants to tap the other on the shoulder it releases chemicals into that gap, including three monoamines: serotonin, dopamine and norepinephrine. These neurotransmitters then float over to the other nerve to get its attention. The first nerve then sucks them back in to be reused the next time it wants to talk. It’s also constantly manufacturing more monoamines, and an enzyme, monoamine oxidase, is constantly chewing them up to maintain just the right amount.

The way cocaine works is by acting as a monoamine reuptake inhibitor. It blocks the first nerve from sucking back up these three chemicals and so there’s a constant tapping on the shoulder—constant signaling—to the next cell. Amphetamines work in the same way but also increase the release of monoamines. Ecstasy works like speed but just causes comparatively more serotonin release.

After awhile, the next nerve may say “enough already!” and down-regulate its receptors to turn down the volume. It puts in earplugs. So you need more and more of the drug to get the same effect, and then when you’re not on the drug you may feel crappy because normal volume transmission just isn’t getting through.

Antidepressants are thought to work along similar mechanisms. People who are depressed appear to have elevated levels of monoamine oxidase in their brain. That’s the enzyme that breaks down those neurotransmitters. In the video, you can see the levels of monoamine oxidase in the brains of depressed individuals versus healthy individuals. The black circles are the levels in the brains of depressed individuals and white circles that of the healthy individuals. If the level of your neurotransmitter-eating enzyme is elevated, then your level of neurotransmitters drops, and you become depressed (or so the theory goes).

So a number of different classes of drugs have been developed. The tricyclic antidepressants, named because they have three rings like a tricycle, appear to block norepinephrine and dopamine re-uptake, and so even though your enzymes may be eating these up at an accelerated rate, what gets released sticks around longer. Then there were the SSRIs (the selective serotonin reuptake inhibitors) like Prozac. Now you know what that means—they just block the reuptake of serotonin. Then there are drugs that just block the reuptake of norepinephrine, or block dopamine reuptake, or a combination. But if the problem is too high levels of monoamine oxidase, why not just block the enzyme? Make a monoamine oxidase inhibitor. Of course they did, but monoamine oxidase inhibitors are considered drugs of last resort because of serious side effects—not the least of which is the dreaded “cheese effect,” where eating certain foods while on the drug can have potentially fatal consequences. If only there was a way to dampen down the activity of this enzyme without the whole bleed-into-your-brain-and-die thing.

Now we can finally talk about the latest theory as to why fruits and vegetables may improve our mood. There are inhibitors of the depression-associated enzyme in various plants. There are phytonutrients in spices, such as clove, oregano, cinnamon, and nutmeg, that inhibit monoamine oxidase, but people don’t eat enough spices to get enough into the brain. A certain dark green leafy has a lot, but its name is tobacco, which may actually be one of the reasons cigarettes make smokers feel so good. OK, but what if you don’t want brain bleeds or lung cancer? Well, there is a phytonutrient found in apples, berries, grapes, kale, onions, and green tea that may indeed affect our brain biology enough to improve our mood, which may help explain why those eating plant-based diets tend to have superior mental health.

For other natural treatments for mental illness, check out:

In health,
Michael Greger, M.D.

PS: I got some feedback from those that previewed this video on DVD that my explanation of MAO inhibition was a bit much. I think there are different camps of viewers. Some that just want to know the bottom-line, and others that are fascinated by the underlying mechanisms and are eager to learn the underlying biology (the “why” not just the “what” and “how”). I’d be interested in everyone’s feedback. Do these more in-depth explanations add or detract from the educational value?

PPS: If you haven’t yet, you can subscribe to my free videos here and watch my live year-in-review presentations Uprooting the Leading Causes of Death and More Than an Apple a Day.

Boost Serotonin Naturally
Green Tea Brain Wave Alteration
Improving Mood Through Diet


Christine Jones
Christine J2 years ago

I appreciate the in-depth information here. Much more useful than the more common, airy-fairy stuff.

Your comment on tobacco makes a lot of sense to me, which is why it is so cruel that patients in mental health facilities are often prevented from smoking. Yes of course it's not healthy, but sometimes it's the last thing in their lives that gives them any pleasure. Plus it's their home, often through no choice of their own, so it's their business if they smoke, so long as they don't expose others to it. I believe we should concentrate on getting people well enough to leave hospital, and then worry about their diet, exercise, smoking and everything else.

Your explanation goes a long way towards explaining why anti-depressants are often great in the beginning, and then lose effectiveness. This can be a really cruel blow to those who feel they've found a "cure" and then slowly get worse. The beauty of vegetables is that they have no side effects and even if they don't help your depression they are still doing you good.

Marie W.
Marie W3 years ago

Mood can be influenced by so many things.

Vicky P.
Vicky P3 years ago

for some maybe, thanks

Elena T.
Elena P3 years ago

Thank you :)

Fred Hoekstra
Fred Hoekstra3 years ago

Thank you Dr. Michael Greger, for Sharing this!

Elena T.
Elena P3 years ago

Thank you :)

Bonnie M.
Bonnie M3 years ago

Good to highlight the importance of a healthy diet, lifestyle and the like. Society is stressed beyond belief and its victims are getting younger. To add to a healthy diet- a commercial puts it this way- Let us add more physical play to the lives of our children and ours.

Lynn C.
Lynn C3 years ago


Ken W.
Ken W3 years ago


Steve McCrea
Steve McCrea4 years ago

Too bad the monoamine hypothesis of depression was thoroughly discredited in the mid-1980s. Not to say that monoamines aren't involved, but serotonin deficiency has NOT been found to be universal or even all that common amongst depressed people.

And based on your statements about cocaine and "down-regulation," it should be obvious that increasing one's serotonin by artificial means will create the same kind of "down regulation" in the serotonin system, which has been scientifically verified. So taking antidepressants, while it may make us feel better in the short run, may also create a dependency on continued or increased antidepressant intake to avoid serotonin shutdown.

Which makes the idea of vegetables to improve mood sound pretty appealing.

---- Steve