It’s crazy when you think about all of the different kinds of food we eat.
We just swallow and hope it all works out for the best.
Well, it turns out there are better ways
to think about keeping our bodies humming healthfully along.
Welcome to Nutrition Facts.
I’m your host Dr. Michael Greger.
Today, we look at ways to mitigate a serious mental health disorder: depression.
There is accumulating evidence that brain-derived
neurotrophic factor (BDNF) may be playing a role in human depression.
BDNF controls the growth of new nerve cells, and “so,
low levels [may explain the] atrophy of specific brain areas…
[you see] among depressed patients.”
That may be one of the reasons exercise is so good for our brains.
Start an hour-a-day exercise regimen, and within three months
you can get a quadrupling of BDNF release from your brain.
This makes sense. Any time we were desperate to catch prey
or desperate not to become prey ourselves,
we needed to be cognitively sharp.
And so, when we’re fasting or exercising and in a
negative calorie balance, our brain starts churning out BDNF
to make sure we’re firing on all cylinders.
So, of course Big Pharma is eager to create drugs to mimic
this effect, but is there any way to boost BDNF naturally?
Yes, I just said it— fasting and exercise!
Okay, okay, but is there anything we can add to our diet to boost BDNF?
Well, higher intakes of dietary flavonoids appear to
be protectively associated with symptoms of depression.
The Harvard Nurse’s Study followed tens of thousands of women
for years and found that those who were eating the most
appeared to reduce their risk of coming down with depression.
Flavonoids occur naturally in plants, and so there’s
a substantial amount in a variety of healthy foods.
But wait…how do we know the benefits are from the flavonoids
and not just from eating healthier in general?
You don’t know until you ... put it to the test.
See, some fruits and vegetables have more than others.
Apples have more than apricots, plums more than peaches,
red cabbage more than white, kale more than cucumbers.
So, if you randomize people into one of three groups:
more high-flavonoid fruits and vegetables, more low-flavonoid fruits
and vegetables, or no extra fruits and vegetables at all,
after 18 weeks, only the high-flavonoid group got
a significant boost in BDNF levels, which corresponded
to an improvement in cognitive performance.
The BDNF boost may help explain why each additional
daily serving of fruits and vegetables is associated with
a three percent decrease in the risk of depression.
A teaspoon a day of the spice turmeric may boost BNDF levels
more than 50 percent within a month, consistent with the other
randomized controlled trials that have so far been done.
Nuts may help too. In the PREDIMED study where people were randomized
to be sent weekly batches of nuts or extra virgin olive oil,
the nut group lowered their risk of having low BDNF levels by 78 percent.
And brain-derived neurotrophic factor is not just implicated
in depression but schizophrenia as well.
Have those with schizophrenia undergo a 12-week exercise program
and they get a significant boost in BDNF levels,
leading the researchers to suggest “that exercise induced modulation
of BDNF may play an important role in developing non-pharmacological
treatment for chronic schizophreni[a] patients.”
Okay, but what actually happened to their schizophrenia symptoms.
Let’s find out.
Thirty individuals with schizophrenia randomized to ramp up
to 40 minutes of aerobic exercise three times a week or not.
And there did appear to be an improvement in psychiatric symptoms
such as hallucinations, as well as increasing their quality of life.
In fact, you can actually visualize what happened in their brains.
Loss of brain volume in a certain region appears to be a feature
of schizophrenia, but 30 minutes of exercise three times a week
and you can get up to a 20 percent increase in size
of that region within three months.
Calorie restriction may also increase BDNF levels in schizophrenics,
but they didn’t just have them eat less, but eat healthier—
less saturated fat and sugar, and more fruits and veggies.
It’s like the Soviet fasting trials for schizophrenia.
They reported these truly unbelievable results,
supposedly restoring people to function, fasting described as
an “unparalleled achievement in the treatment of schizophrenia”.
Okay, but part of the problem is that the diagnostic system
the Soviets used is completely different, making any results
hard to interpret. But they do have a subgroup that does
seem to correspond to the Western definition, and they still report
between 40 and 60 percent improvement rates from fasting.
But that's not all they did. After being fasted for up to a month,
they were put on a meat and egg-free diet,
so when they report these remarkable effects even years later,
that’s for those who stuck with the diet.
Those who broke the diet evidently relapsed,
and the closer the diet was followed the better the effect.
They note that “not all patients [were able to] remain vegetarian,”
but they tried to keep meat to a minimum.
And look, we know from randomized controlled trials that just
removing meat and eggs can improve mental states within even
just two weeks, and so it’s hard to know what role
the fasting itself played in the reported improvements.
A single high-fat meal can drop BDNF levels within hours.
And you can prove it’s the fat itself by seeing the same thing
injecting fat straight into their veins.
Perhaps that helps explain why increased consumption of
saturated fats in a high-fat diet may contribute to brain dysfunction—
neurodegenerative diseases, long-term memory loss, cognitive impairment.
Maybe that helps explain why the standard American diet has been
linked to a higher risk of depression, dietary factors modulating
the levels of brain-derived neurotrophic factor.
If depression can be induced with pro-inflammatory drugs,
might an anti-inflammatory diet be effective in preventing and treating mood disorders?
Depression affects more than 150 million people worldwide,
making it a leading cause of losing healthy years of life
as a result of disability.
In fact by 2020, depression may be the second leading cause
of healthy years of life lost, second only to heart disease.
Why is depression so common?
Well, it is said “Nothing in biology makes sense except
in the light of evolution,”
but why would be evolve to get depressed?
Depression poses a baffling evolutionary puzzle.
It has such negative effects, but remains so common and heritable,
meaning a big chunk of risk is passed down through our genes,
so there must be some kind of adaptive benefit.
Otherwise, presumably, it would have been naturally selected against.
Maybe, depression is an evolutionary strategy for defense against infection.
Infection has been the leading cause of mortality
throughout human history.
The average life expectancy was 25,
and it was not uncommon for half our kids to die.
With such stark capabilities, infection has been a critical
and potent driving force in natural selection.
When we become infected, there is a surge of inflammation
as our body mounts a counterattack, and then what happens?
We feel lousy. We feel sick, we get weak, tired, slow, and sleepy.
We don’t see anyone; we don’t want to do anything;
all we want to do is sleep.
It’s like we’re depressed—
and that’s great for fighting infection.
Not only does that help us conserve energy so we can
put up a good fight, but reduces social contact,
we’re not running around infecting everyone.
It’s the same reason we evolved to think poop doesn’t smell good,
or decaying flesh.
That keeps us safe from infection.
In fact, we see this phenomenon with other social animals
like honeybees and mole rats
who feel impelled to crawl off and die alone when they get sick,
which reduces the risk to the rest of the community.
The relationship between mental health and inflammation
was first noted in 1887, for which the only psychiatrist
to ever win the award got a Nobel Prize.
But what evidence have we accumulated in the century since
that inflammation causes depression?
Well, people who are depressed have raised inflammatory markers
such as C-reactive protein.
Inflammatory illnesses are associated with greater rates of major depression.
Indeed, that’s what’s found in a variety of inflammatory conditions
including more benign inflammatory conditions,
like as asthma and allergies,
and that’s important, suggesting the mood symptoms
are not simply ‘feeling bad about having a terrible disease’
but may be directly tied to the inflammation.
Most powerfully, you can actually induce depression
by inducing inflammation, like when we give interferon
for certain cancers or chronic infections—
up to 50% go on to suffer major depression.
Even just giving a vaccine can cause enough inflammation
to trigger depressive symptoms.
Taken together, these studies are strongly suggestive of
inflammation being a causative factor of mood symptoms.
So can an anti-inflammatory diet help prevent depression?
We didn’t know…
until about 43,000 women without depression were followed,
along with their diets, for about a dozen years
to see who became depressed, and it was those who at a more
inflammatory dietary pattern,
characterized by more soda, refined grains and meat,
suggesting that chronic inflammation may underlie the association
between diet and depression.
Normally, we think of omega-3’s as anti-inflammatory,
but they found fish to be pro-inflammatory,
associated with increased C-reactive protein levels consistent with recent findings
that omega-3’s don’t seem to help with either depression or inflammation.
The most anti-inflammatory diet is plant-based,
which can cut C-Reactive Protein levels by 30% within two weeks.
Perhaps because of the anti- inflammatory properties of antioxidants.
I’ve talked about this before, but never explained WHY
antioxidants are anti-inflammatory.
Oxidative damage caused by free radicals may cause
an autoimmune response in the body by changing the chemical structures
of otherwise ubiquitous molecules to generate new structures
that the body attacks as foreign.
For example, when LDL cholesterol gets oxidized,
our body creates antibodies against it and attacks it.
And so clinical depression can be accompanied by increased oxidative stress
and the autoimmune inflammatory responses it creates.
Free radicals lead to auto-immune inflammation.
Where else does inflammation come from in our diet?
Endotoxins. It’s worth reviewing how the endotoxins in animal products
can cause a burst of inflammation within hours of consumption.
What does it do to our mood?
If you inject endotoxin into people, within a few hours, inflammation shoots up,
and so does feelings of depression,
as well as feelings of social disconnection from people.
Although previous research has demonstrated that inflammatory activity
contributes to depressive symptoms,
no work in humans has examined the effect of experimentally induced
inflammation on anhedonia—
a key diagnostic feature of depression,
as well as anhedonia, the lack of reaction to pleasurable stimuli—
this is an an important symptom of depression.
No work has been done that is....
until now.
Within hours of endotoxin hitting their bloodstream,
these experimental subjects not only started to feel depressed,
but they had significant reductions in activity
in the reward center of the brain.
They were less excited about winning money
playing video games, for example in the study.
But by eliminating animal products, and eating antioxidant rich diets,
we may be able to prevent or treat depression.
The most comprehensive controlled trial of diet and mood
finds that a plant-based nutrition program in a workplace setting
across ten corporate sites significantly improves depression, anxiety, and productivity.
A 2014 systematic review and meta-analysis of dietary patterns
and depression concluded that a healthy diet pattern was significantly associated
with the reduced odds of depression.
But out of the 21 studies they could find in the medical literature,
they were only able to find one randomized controlled trial,
considered the study design that provides the highest level of evidence.
And it was the study I profiled in "Improving Mood Through Diet",
in which removing meat, fish, poultry and eggs
improved several mood scores in just two weeks.
We've known those eating plant-based tend to have healthier mood states
less tension, anxiety, depression, anger, hostility and fatigue,
but you couldn't tell if it was cause and effect
until you put it to the test, which they finally did.
But what could account for such rapid results?
Well, eating vegetarian does give you a better antioxidant status,
which may help with depression.
Also, as I've previously addressed,
how consumption of even a single carbohydrate-rich meal
can improve depression, tension, anger, confusion, sadness, fatigue, alertness,
and calmness scores among patients with PMS, but what about long term?
Overweight men and women were randomized into a low carb, high fat diet
or high carb, low fat diet for a year.
By the end of the year, who had less depression, anxiety, anger and hostility,
feelings of dejection, tension, fatigue, better
vigor, less confusion or mood disturbances?
These sustained improvements in mood in the low fat group
compared with the low carb group
are consistent with results from epidemiological studies
showing that diets high in carbohydrate and low in fat and protein
are associated with lower levels of anxiety and depression
and have beneficial effects on psychological well-being.
The overall amount of fat in their diet didn't change in this study, though.
But the type of fat did.
Their arachidonic acid intake fell to zero.
Arachidonic acid is an inflammatory omega-6 fatty acid
that can adversely impact mental health via a cascade of neuroinflammation.
It may inflame our brain.
High blood levels in the bloodstream have been associated
with a greater likelihood of suicide risk, for example,
and major depressive episodes.
How can we stay away from the stuff?
Well, Americans are exposed to arachidonic acid
primarily through chicken and eggs.
But when you remove chicken and eggs, and other meat,
we can eliminate preformed arachidonic acid from our diet.
So while high-quality treatment studies investigating the impact of diet
on depression are scarce, there is that successful 2-week trial,
but even better: How about 22 weeks?
Overweight or diabetic employees of a major insurance corporation
received either weekly group instruction on a whole food plant-based diet
or no diet instruction for five and a half months.
There was no portion size restriction, no calorie counting, no carb counting.
No change in exercise.
No meals were provided, but the company cafeteria did start offering
daily options such as lentil soup, minestrone, bean burritos.
No meat, eggs, dairy, oil or junk, yet they reported greater diet satisfaction
compared with the control group participants who had no diet restrictions.
How'd they do though?
More participants in the plant-based intervention group
reported improved digestion, increased energy, better sleep than usual
at week 22 compared with the control group.
They also reported a significant increase in physical functioning,
general health, vitality, and mental health,
where the plant-based group beat out controls on nearly every measure.
There was also significant improvements in work productivity,
thought to be due in large part to their improvements in health.
So what this study demonstrated was that a cholesterol-free diet is acceptable,
not only in research settings, but in a typical corporate environment,
improving quality of life and productivity at little cost.
All we need now is a large, randomized trial for confirmation,
but we didn't have such a thing, until now.
Ten corporate sites across the country from San Diego to Macon, Georgia.
Same kind of set up as before.
Can a plant-based nutrition program in a multi-center, corporate setting
improve depression, anxiety, and productivity?
Yes. Significant improvements in depression, anxiety, fatigue,
emotional well being, and daily functioning.
Lifestyle interventions have an increasingly apparent role
in physical and mental health, and among the most effective
of these is the use of plant-based diets.
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please go to the Nutrition Facts Podcast landing page.
There you’ll find all the detailed information you need –
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