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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

Read more: Health, Depression, Diet & Nutrition, Eating for Health, General Health, Mental Wellness, Videos, ,

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Dr. Michael Greger

A founding member of the American College of Lifestyle Medicine, Michael Greger, M.D., is a physician, author, and internationally recognized speaker on nutrition, food safety, and public health issues. Currently Dr. Greger serves as the Director of Public Health and Animal Agriculture at The Humane Society of the United States. Hundreds of his nutrition videos are freely available at


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9:32PM PDT on Oct 27, 2013

Mood can be influenced by so many things.

9:30PM PDT on Oct 27, 2013

for some maybe, thanks

5:10PM PDT on Oct 26, 2013

Thank you :)

5:55AM PDT on Oct 26, 2013

Thank you Dr. Michael Greger, for Sharing this!

1:28AM PDT on Oct 24, 2013

Thank you :)

2:01PM PDT on Oct 22, 2013

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.

7:27PM PDT on Oct 21, 2013


7:01PM PDT on Oct 21, 2013


9:51AM PDT on Oct 21, 2013

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

10:22PM PDT on Oct 20, 2013


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people are talking

80 %, thank you .... great questions


I should have qualified "close-up" as right in front of their nose/face. A few inches away they can …

Very scary. Hopefully this is a far from typical situation.


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