How Many Servings of Fruits and Vegetables to Improve Mood?

“Thousands of papers have been published on the important topic of what determines people’s subjective well-being and psychological health,” but what about the potential influence of the different kinds of foods people eat? I explore this in my video Which Foods Increase Happiness?.

“The rising prevalence of mental ill health is causing considerable societal burden. Inexpensive and effective strategies are therefore required to improve the psychological well-being of the population….A growing body of literature suggests that dietary intake may have the potential to influence psychological well-being.” Dietary intake of what? Well, given the strong evidence base for the health benefits of fruits and vegetables, researchers started there.

Cross-sectional studies from all over the world support this relationship between happiness and intake of fruits and vegetables. Those eating fruits and vegetables each day have “a higher likelihood…of being classified as ‘very happy,’” suggesting “a strong and positive correlation between fruit and vegetable consumption and happiness” and perhaps feelings of optimism, too.

The largest such study was done in Great Britain, where “a dose-response relationship was found between daily servings of [fruits and vegetables] and both life satisfaction and happiness,” meaning more fruits and veggies meant more happiness. People who got up to seven or eight servings a day “reported the highest life satisfaction and happiness,” and these associations remained significant even after controlling for factors such as income, illness, exercise, smoking, and body weight, suggesting fruit and vegetable consumption didn’t just act as a marker for other healthy behaviors.

But how could eating plants improve happiness on their own? Well, many fruits and veggies contain higher levels of vitamin C, which is “an important co-factor in the production of dopamine,” the zest-for-life neurotransmitter. And, the antioxidants in fruits and vegetables reduce inflammation, which may lead “to higher levels of eudaemonic well-being.”

Eudaemonic? What’s that? “Aristotle’s notion of eudaemoniadescribed the highest of all human goods as the realization of one’s true potential,” which was the aim of a study: Researchers wanted to know whether eating fruits and vegetables was “associated with other markers of well-being beyond happiness and life satisfaction.” So, they tested whether consuming fruits and veggies was associated with “greater eudaemonic well-being—a state of flourishing characterized by feelings of engagement, meaning, and purpose in life.”

The researchers followed a sample of about 400 young adults for 13 days, and, indeed, the young adults who ate more fruits and veggies “reported higher average eudaemonic well-being, more intense feelings of curiosity, and greater creativity.” This could be followed on a day-by-day basis: greater well-being on the days they ate healthier. “These findings suggest that [fruit and vegetable] intake is related to other aspects of human flourishing, beyond just feeling happy.”

Not so fast, though. Instead of eating good food leading to a good mood, maybe the good mood led to eating good food. Experimentally, if you put people in a good mood, they rate healthy foods, like apples, higher than indulgent foods, like candy bars. Given a choice between M&M’s and grapes, individuals in a positive mood were more likely to choose the grapes. The results of these studies “lend support to a growing body of research that suggests that positive mood facilitates resistance to temptation.” Who needs comfort foods when you’re already comforted? It’s like which came first, the stricken or the egg? Yes, eating eggs may increase our likelihood of chronic disease, but maybe chronic disease also increases our likelihood of eating unhealthy foods. Which came first, the mood or the food?

If only there were a study that, instead of looking at well-being and diet on the same day, looked to see if there’s a correlation between what you eat today and how you feel tomorrow.

There is. In the study, researchers found the same “strong relationships between daily positive [mood] and fruit and vegetable consumption.” Additionally, “[l]agged analyses showed that fruit and vegetable consumption predicted improvements in positive [mood] the next day, not vice versa…On days when people ate more fruits and vegetables, they reported feeling calmer, happier and more energetic than they normally do…[and] also felt more positive the next day.” So, eating fruits and vegetables really “may promote emotional well-being.” Single bouts of exercise can elevate one’s mood, so why not the same with healthy food?

How many fruits and vegetables? Seems we “need to consume approximately 7.2 daily servings of fruit or 8.2 servings of vegetables to notice a meaningful change” in mood.


For more on this topic, I invite you to watch Plant-Based Diets for Improved Mood & Productivity.

I mentioned in passing the benefits of exercise for boosting mood, and here is more on maximizing movement:

Sadly, there are 20 times more studies published on health and depression than there are on health and happiness. There is growing interest in the so-called positive psychology movement, though. See my video Are Happier People Actually Healthier? for more.

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations:

Is It Healthier to be Happier?

More than 60 years ago, the World Health Organization defined health as a “state of complete physical, mental, and social well-being and not merely the absence of disease or infirmity.” Just because you’re not depressed doesn’t necessarily mean you’re happy. But, if you look in the medical literature, there are 20 times more studies published on health and depression than there are on health and happiness. In recent years, though, research on positive psychology has emerged, and we’re now asking what we can do to increase our success, functioning, and happiness. Although these are all inherently good in themselves, what about the question I address in my video Are Happier People Actually Healthier?

“There is growing evidence that positive psychological well-being is associated with reduced risk of physical illness,” but it’s not surprising that healthier people are happier than sick people. “The intriguing issue is whether psychological well-being protects against future illness or inhibits the progression of chronic disease.” To figure out which came first, you’d have to get more than just a snapshot in time. You would need prospective studies, meaning studies that go forward over time, to see if people who start out happier do, in fact, live longer. A review of such studies indeed “suggests that positive psychological well-being has a favorable effect on survival in both healthy and diseased populations.”

Not so fast.

Yes, positive states may be associated with less stress, less inflammation, and more resilience to infection. But, positive well-being may also be accompanied by a healthy lifestyle that itself reduces the risk of disease. Happy people tend to smoke less, exercise more, drink less alcohol, and sleep better. So, maybe happiness leads to health only indirectly. The apparent protective effect of positive psychological well-being, however, persists even after controlling for all these healthy behaviors. This means that even at the same level of smoking, drinking, exercising, and sleeping, happier people still seem to live longer.

Ideally, to establish cause-and-effect definitively, we’d do an interventional trial, in which participants would be assigned at random to different mood levels and tracked for health outcomes. It’s rarely feasible or ethical to randomly make some people’s lives miserable to see what happens, but if you pay people enough you can do experiments like the one whose objective stated: “It has been hypothesized that people who typically report experiencing negative emotions are at greater risk for disease and those who typically report positive emotions are at less risk.” Researchers tested this using the common cold virus. Three hundred and thirty-four healthy volunteers were assessed for how happy, pleased, and relaxed they were, or how anxious, hostile, and depressed. Subsequently, they were given nasal drops containing cold rhinoviruses to see who would be more likely to come down with the cold. Who would let someone drip viruses into their nose? Someone paid $800, that’s who!

Now, just because you get exposed to a virus doesn’t mean you automatically get sick. We have an immune system that can fight it off, even if the virus is dripped right into our nose. But, whose immune system fights better?

In one-third of the bummed out folks, their immune systems failed to fight off the virus and they came down with a cold. But only about one in five got a cold in the happy group. Could it be that those with positive emotions slept better, got more exercise, or had lower stress? No. It appears that even after controlling for the healthy practices and levels of stress hormones, happier people still appear to have healthier immune systems and a greater resistance to developing the common cold.

It also works with the flu. When researchers repeated the study with the flu virus, increased positive emotions were associated with decreased verified illness rates, just like in their earlier study on colds. These results indicate that feeling vigorous, calm, and happy may play a more important role in health than previously thought.


Okay, so if happiness improves health, how do we improve happiness? That’s the subject of my video Which Foods Increase Happiness?.

I’m as guilty as the rest of my colleagues for focusing on mental illness rather than mental health (though my Laughter as Medicine video is a rare exception). It’s a consequence of what’s out there in the medical literature, though I’ll make a special effort to highlight new studies in this area as they’re published. I do, however, have a number of videos on preventing and treating negative mood states, such as depression and anxiety:

What about psychiatric medications? See my videos Do Antidepressant Drugs Really Work?, Exercise vs. Drugs for Depression, and Saffron vs. Prozac.

Interested in other ways to improve our immune system? Check out Using the Produce Aisle to Boost Immunity.

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations:

Can Dehydration Affect Our Mood?

Water is by far the number-one nutrient in our diet. Studies have suggested that proper hydration may lower our risk of heart disease and cancer, and may even make us better kissers. Brushing artificial skin against the lips of young women, researchers found that hydrated lips showed greater sensitivity to light touch.

Although it is well known that water is essential for human survival, it’s only recently that we have begun to understand its role in the maintenance of brain function. It makes sense. Our brain is 75% water. When we get dehydrated, our brain actually shrinks. Even mild dehydration, which can be caused by simply exercising on a hot day, has been shown to change brain function.

I’ve talked about the role of hydration for cognitive function in Does a Drink of Water Make Children Smarter?, but current findings suggest that our mood states may also be positively influenced by water consumption.

The effects of dehydration in real life have not been not well documented. It wasn’t until 2013 that the first study to investigate the effects of mild dehydration on a variety of feelings was published. What did the researchers find? The most important effects of fluid deprivation were increased sleepiness and fatigue, lower levels of vigor and alertness, and increased confusion. But as soon as they gave the subjects some water, the deleterious effects on alertness, happiness, and confusion were immediately reversed.

Water absorption actually happens very rapidly, within 5 minutes from mouth to bloodstream, peaking around minute 20. Interestingly, the temperature of the water appears to affect this speed. Which do you think is absorbed more rapidly—cold water or warm, body temperature water? It turns out cold water gets sucked in about 20% faster!

How can we tell if we’re dehydrated or not? Well, why don’t we ask our bodies? If we chug down some water and then turn around and just pee it all out, presumably that would be our body’s way of saying, “I’m good, all topped off.” But if we drink a bunch of water and our body keeps most of it, then presumably our tank was low. Researchers from the University of Connecticut formalized the technique. You empty your bladder, chug down 11 milliliters per kilogram of body weight (about 3 three cups of water for an average-sized person) and then an hour later see how much you pee. Basically, if you drink 3 cups and pee out less than 1, there’s a good chance you were dehydrated. You can see the findings of this chug-and-pee test around minute 3 in my Can Dehydration Affect Our Mood? video.


For more on water, see my How Many Glasses of Water Should We Drink a Day?Does a Drink Of Water Make Children Smarter?, and Treating Dry Eyes with Diet: Just Add Water? 

Other healthy beverages include hibiscus tea (Hibiscus Tea vs. Plant-Based Diets for Hypertension) and green tea (Dietary Brain Wave Alteration and Benefits of Green Tea for Boosting Antiviral Immune Function).

What else can affect our mood?

What about the omega-3s in fish? That’s the subject of another video: Fish Consumption and Suicide.

In health,

Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations: