Natural monoamine oxidase enzyme inhibitors in fruits and vegetables may help explain the improvement in mood associated with switching to a plant-based diet.
Images thanks to practicalowl and gloom via Flicker and Mouagip, Nrets, Dake, ThePallanz, and Savant-fou via Wikimedia Commons. Thanks to Ellen Reid, Maxim Fetissenko, PhD, and Laurie-Marie Pisciotta for their help with Keynote.
Why does frequent consumption vegetables appear to cut ones odds of depression by more than half? And by more frequent they mean eating vegetables not 3 or more times a day, but just 3 or more times a week. But even that seemed to cut the odds of developing depression by 60% after controlling for a long list of variables.
In the 2012 study that found that eliminating animal products improved mood within 2 weeks. The researchers blamed arachidonic acid, primarily in chicken and eggs, which may adversely impact mental health via a cascade of brain inflammation, 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. This 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?
Well to understand the latest, we need to understand the underlying biology, the so-called monoamine theory of depression, the thought 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. Here's the end of one nerve and the beginning of another.
This is what it actually looks like under amicroscope. 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, but it's also constantly manufacturing more 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 this constant tapping on the shoulder this constant signaling to the next cell. Amphetamines work in the same way but also increase their release. Ecstacy works like speed but just causes comparatively more serotonin release.
After awhile, the next nerve may be like 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, and so if you have too much of that enzyme in critical parts of your brain, as the study show—the black circles are the levels in the brains of depressed individuals, and white circles that of the healthy individuals, if your levels of your neurotransmitter-eating enzyme is elevated, then your levels 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 like Prozac, the selective serotonin reuptake inhibitors. Now you know what that means—just blocks the reuptake of serotonin. Then there are drugs that just block the reuptake of norepinephrine. Or more dopamine. Or the opposite. But if the problem is too high levels of monoamine oxidase, why not just block the enzyme? Make a monoamine oxidase inhibitor—and of course they did, but they're 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 tamp 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, but people don't eat enough spices to get enough into the brain. This 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, and grapes, and kale, onions, and green tea that may indeed affect our brain biology enough to improve our mood.
To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video. This is just an approximation of the audio contributed by Ariel Levitsky.
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More on the inflammatory omega-6 arachidonic acid in chicken and eggs that may impact mental health via a cascade of brain inflammation in:
For other natural treatments for mental illness, check out:
I got some feedback from those that previewed this video on DVD that my explanation of MAO inhibition was a bit much (too complicated). I think there are different camps of NutritionFacts.org 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?
For more context, check out my associated blog post: Can We Fight the Blues with Greens?
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