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:

Why Drugs and Diet Can Sometimes Fail in Diabetes

“People with type 2 diabetes are at elevated risk for a number of serious health problems, including cardiovascular disease, premature death, blindness, kidney failure, amputations, fractures, frailty, depression, and cognitive decline.” In other words, the higher people’s chronic blood sugars are, the more heart attacks and strokes they have, the shorter their lifespans, and the higher their risk of complications such as blindness and kidney failure, which I discuss this in my video When Drugs and Diets Don’t Lower Diabetes Deaths.

A study was designed in which 10,000 diabetics were randomized into an intensive blood sugar-lowering intervention, where they put people on one, two, three, four, or five different classes of drugs, with or without insulin, to drive blood sugars into the normal range. Of course, this is not treating the underlying cause—that is, the actual disease—but by lowering one of the effects of the disease by any means necessary, these high blood sugars, the hope was to prevent some of the devastating complications. How did they do?

The intensive blood sugar lowering with drugs increased mortality. After reviewing mortality trends, they concluded that the harm associated with the increased risk of death outweighed any potential benefits, and they stopped the study prematurely for safety reasons. They were successful in bringing down people’s blood sugar, but in trying to push people’s hemoglobin A1c under six, they ended up pushing people six feet under. They speculated that this may have been due to the adverse effects of the very drugs used to treat the disease.

Even just injected insulin itself may promote cancer, obesity, and atherosclerosis, worsen diabetic eye disease, and accelerate aging. Insulin therapy may promote inflammation in the lining of our arteries, which may help explain the results of that drug trial and other trials like it that showed the same thing: no reduction in so-called “macrovascular” complications—heart attacks and strokes—with intensive blood sugar lowering. However, intensive therapy was associated with a 21 percent reduction in the development of microvascular complications like kidney dysfunction.

Any such benefits should be weighed against the increased risk of dying, increased weight gain, and increased risk of severe hypoglycemia in intensively treated patients. So, trying to normalize people’s blood sugar with medications alone may not be the best  idea. “It also should be noted that these trials relied virtually exclusively on [drugs] and did not include any serious effort at [diet and other] lifestyle change…”.

A study published in the New England Journal of Medicine found that an intensive lifestyle intervention focusing on weight loss did not reduce the rate of cardiovascular events such as heart attacks in overweight or obese adults with type 2 diabetes. It did not increase their risk of death, but it didn’t seem to decrease it either. In fact, the trial was stopped after about 10 years on the basis of futility—participants lost weight, but they weren’t dying any less. That’s what we see across the board with these types of lifestyle interventions. It’s good that the dietary intervention wasn’t killing anyone, but why wasn’t it actually helping people live longer?

Because they didn’t actually put them on a healthier diet.

They just put them on a smaller diet––a calorie-restricted diet––meaning essentially the same lousy diet, but just in smaller portions. If we eat less and exercise more, we can lose weight, get more physically fit, get slimmer, and have better blood sugar control, but if our diets continue to be so un-heart-healthy that our bad LDL cholesterol doesn’t improve, we’re not going to be unclogging our arteries. Whereas individuals following healthier diets may experience not only improved reductions in blood sugar and body weight, but cardiovascular risk as well. Yes, by eating a smaller quantity of food, without changing quality, we can lose weight, but the point of a lifestyle intervention is not to just fit people into skinnier caskets.


What kind of diet does help diabetics? See How Not to Die from Diabetes and Plant-Based Diets & Diabetes. You’ve probably heard that Diabetics Should Take Their Pulses. Why is that the case? See Why Is Meat a Risk Factor for Diabetes? and How May Plants Protect Against Diabetes?.

Healthier diets can even reverse some of the complications of diabetes once thought irreversible. See Can Diabetic Retinopathy Be Reversed? and the part of my annual review From Table to Able: Combating Disabling Diseases with Food that discusses the remarkable reversal of painful diabetic neuropathy.

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: