“Fruits and Vegetables Put to the Test for Boosting Mood”
There are two components of psychological health: the absence
of mental health disorders such as depression, as well as
the existence of positive psychological well-being.
That's the focus of an emerging field of positive psychology
focusing on happiness, life satisfaction, and flourishing,
which may translate to physical benefits such as improvements
in blood pressure, immune function, and longevity.
What is the contribution of food consumption to well-being?
Well, studies have linked the consumption of fruits and vegetables
with enhanced well-being. A systematic review of research found evidence
that consuming fruits and vegetables was associated with
increased psychological well-being. Okay, but that's just an association.
A famous criticism in this area of research is that maybe there's just
some inherent personality trait or type of family upbringing
that might lead people simultaneously
to eat in a healthy way, and also to have better mental well-being.
So the diet is merely correlated with, but incorrectly gives
the appearance of helping to cause the level of well-being.
But recent research circumvented this problem by seeing
if changes in diet are correlated with changes in mental well-being,
in effect studying the evolution of well-being and happiness
after increases in the consumption of fruits and vegetables.
And look at that graph—a straight-line increase between how much more fruits
and veggies people started eating and their change in life satisfaction
over time. Increased fruit and vegetable consumption appeared
predictive of increased happiness, life satisfaction, and well-being—
up to 0.24 life-satisfaction points for an increase of eight portions a day.
What does that mean? Is that a lot? Is that a little?
That's a lot, equal in size to the psychological gain
of going from unemployed to getting a job.
My Daily Dozen recommendation is for at least nine servings
of fruits and veggies a day.
This study was done in Australia. It was repeated in the UK, and
researchers there found the same thing, though the Brits may need
to bump up their daily minimum to more like 10 or 11 servings a day.
Okay, but does eating fruits and veggies also reduce the risk of depression
and anxiety? I mean well-being is nice,
but governments and medical authorities are often interested
in the determinants of major mental illness, not life satisfaction.
And indeed, using the same data set but instead looking for mental illness,
eating fruits and vegetables may help to protect against future risk
of clinical depression and anxiety as well.
A systematic review and meta- analysis of dozens of studies found
that every 100-gram increased intake of fruit was associated with a 3% reduced
risk of depression. That's about half an apple, yet less than 10%
of most Western populations even consume a bare minimum.
Maybe the problem is we're just telling people about the long-term benefits
of fruit intake for chronic disease prevention,
rather than the near-immediate improvements in well-being.
So maybe we should be advertising the happiness gains,
but first we need to make sure they're real.
We've been talking about associations. Yes, a healthy diet may reduce the risk
of future depression or anxiety, but being diagnosed with depression
or anxiety today could also lead to lower fruit and vegetable intake.
Now, in these studies you can indeed show that the increase in fruit
and vegetable consumption came first, and not the other way around,
but as the great enlightenment philosopher pointed out,
just because the cock crows before the dawn
doesn't mean the cock caused the sun to rise.
To prove cause-and-effect
you need to put it to the test with an interventional study.
Unfortunately, to date many studies were like this,
where those randomized to eat fruit showed significant improvements
in anxiety and depression, fatigue, and emotional distress.
Wow, amazing! But that was compared to chocolate and potato chips.
Apples, clementines, and bananas making people feel better than assorted
potato chips and chunky chocolate wafers—not exactly a revelation.
This is the kind of study I've been waiting for: a randomized controlled
trial in which young adults were randomized to a diet-as-usual group,
encouragement to eat more fruits and veggies,
or a third group given two servings of fruits and vegetables a day
to eat over and above their regular diet.
And the ones given fruits and veggies showed improvements
in their psychological well-being with increases in vitality, flourishing,
and motivation within just two weeks!
However, simply educating people to eat their fruits and vegetables
may not be enough to reap the full rewards,
so perhaps greater emphasis needs to be placed on actually providing people
with fresh produce, for example, offering free fruit for people when they shop.
I know that would certainly make me happy!