New findings bolster and detail the brain benefits of plant-rich diets 06/06/2019
A good deal of evidence suggests that seafood-source omega-3s support — and may enhance —mood and mental health.
For example, see Omega-3 Trial in Seniors Finds Mood & Brain Benefits, Omega-3s May Rival Antidepressant Drugs, and related articles in the Omega-3s/Brain Health section of our newsletter archive.
Likewise, a fast-growing body of evidence links “green” diets — ones rich in fruits and vegetables — to better moods and mental health.
We covered some of this research in Healthy Diets May Help Deflect Anxiety & Depression, Top 5 Foods for Boosting Mood, Can Food Really Lift Your Mood?, and other articles in the Brain Health & Food section of our newsletter archive.
Conversely, there’s also evidence that junky diets — ones featuring fast foods — can be depressing: see Fast Foods Look Even Worse in New Findings.
Four recently published studies bolster — and add detail to — prior findings about the apparent brain/mood benefits of diets rich in fruits and vegetables.
We’ll start by describing a pair of studies from British universities that carry unusual weight, thanks to their large numbers of participants, then scan the results of two studies from New Zealand.
Study #1: “Lettuce be happy” paper links fruits and veggies to mental well-being
This large epidemiological (population) study comes from economists and social scientists at the universities of Leeds and York.
This research team analyzed survey data gathered from more than 40,000 people in the UK who were followed for varying periods lasting several years (Ocean N et al. 2019).
As you'd expect, they adjusted their calculations to account for the effects of other factors known to affect mental well-being — including age, education, income, marital status, employment status, lifestyle and health — as well as consumption of other foods, such as meats, vegetable oils, and grain or dairy products.
After accounting for all these possible “confounding” factors, the researchers’ analysis linked greater consumption of fruits and vegetables to better mental well-being.
Specifically, they calculated that just one extra daily serving of fruits and vegetables equaled the known mental health benefits of about 8 extra days of walking (at least 10 minutes at a time) per month.
As economist and study co-author Dr. Ocean said, “Our research builds on previous work in Australia and New Zealand by verifying this relationship using a much bigger UK sample … [and] … the results are clear: people who eat more fruit and vegetables report a higher level of mental well-being and life satisfaction than those who eat less.”
Study #2: British team quantifies the mood benefits of fruits and veggies
Researchers from Britain’s University of Warwick published enlightening findings that add detail to the links between plant foods and mood.
Dr. Redzo Mujcic and Professor Andrew Oswald led the study, in which they analyzed data from respondents to Australia’s annual Household, Income and Labour Dynamics survey (Mujcic R, Oswald AJ 2019).
Survey participants were asked whether they’d been diagnosed with depression or anxiety, and questions about their diets and lifestyles.
The study focused on the 7,108 respondents who said they hadn’t been diagnosed with depression or anxiety, to see if their diets might protect their chance of depression two years later.
And the results linked eating more fruit and vegetables to a lower likelihood that mentally healthy would later be diagnosed with depression, anxiety, or another a mental problem.
“If people increase their daily intake of fruit and vegetables from zero to eight [servings] they are 3.2 percentage points less likely to suffer depression or anxiety in the next two years,” said Dr Mujcic.
Specifically, the British team’s analysis linked eating four extra portions of fruit and vegetables a day to a boost in people’s mental health big enough to offset half the depressing impact of divorce and a quarter of the depressing impact of unemployment.
Dr. Mujcic stressed the relative speed of the mood benefits of a green diet, versus its physical benefits: “And the effect is a lot quicker than the physical improvements you see from a healthy diet. The mental gains occur within 24 months, whereas physical gains don’t occur until you are in your 60s.”
Importantly, the British team couldn’t find significant evidence that depression or anxiety might have led people to eat fewer fruit and vegetables.
Dr Mujcic noted the need for randomized controlled clinical trials to confirm (or refute) the apparent cause-effect relationship between diets rich in fruits and vegetables and better mental health.
Study #3: Raw produce may be better than cooked
A study from New Zealand’s University of Otago indicated that raw fruits and vegetables may boost mental well-being more than their cooked counterparts (Brookie KL et al. 2018).
Psychologist and lead author Dr. Tamlin Conner said that public health campaigns have focused on the quantity of fruit and vegetables people should consume for optimal health, so her team decided to look for any differences between raw and cooked produce.
For the study, they surveyed 422 men and women aged 18 to 25 from New Zealand and the United States. (Young adults were chosen because — among all age groups — they typically eat the fewest fruits and vegetables and are at the highest risk for mental health disorders.)
The participants were asked about their typical diets, including their consumption of raw versus cooked and processed fruits and vegetables. They also answered questions about their mental health and lifestyle and demographic factors known to affect mental health (e.g., exercise, sleep, chronic health conditions, smoking, alcohol use, socioeconomic status, ethnicity, and gender.)
After adjusting their calculations to account for the effects of the other variables, the team’s analysis linked greater consumption of raw fruits and vegetable consumption to fewer symptoms of depression, and higher levels of psychological well-being — including positive mood, greater life satisfaction, and a greater sense of flourishing.
In contrast, mental health status was significantly worse among respondents who reported comparable consumption of cooked, canned and/or processed fruits and vegetables.
The top 10 raw foods linked to better mental health were carrots, bananas, apples, dark leafy greens like spinach, grapefruit, lettuce, citrus fruits, fresh berries, cucumber, and kiwifruit.
Dr. Conner and her co-authors speculated that the difference might come down to the fact that cooking and processing of fruits and vegetables can diminish levels of nutrients essential to, or beneficial for, mental health.
The New Zealand researchers are conducting a randomized, controlled clinical trial designed to test the mental health effects of kiwifruit — the raw plant food most strongly linked to better mental health.
That trial will focus on young adults who have very low vitamin C levels because they haven’t been eating many fruit and vegetables, and don't take vitamin C supplements. The participants are being asked to eat two kiwifruit a day for 30 days, to see whether and how that change might affect their mental health and wellbeing.
Dr. Conner hopes that establishing such a link it could influence people’s food choices: “If eating that banana makes you less grumpy when you go home at night, then it's useful information.”
Study #4: Prior New Zealand study found fast fruit-vegetable benefits
In a study published a year earlier, Dr. Conner’s New Zealand team tested the psychological benefits of inducing young adults to eat more fruits and vegetables (Conner TS et al. 2017).
The researchers divided 171 male and female volunteers into two groups:
- Control group, who ate their usual diet.
- Test group #1, who were sent “eat more produce” text reminders and given coupons to purchase fruits and vegetables, with the goal of getting them to eat two additional daily servings of fresh fruits and vegetables.
- Test group #2, who were given two additional daily servings of fresh fruits and vegetables to consume on top of their normal diets.
Before and after the 14-day trial, the participants answered a smartphone survey designed to reveal any symptoms of depression or anxiety, as well as their daily mood and positive signs such as curiosity, creativity, and motivation.
In addition, the participants' blood levels of vitamin C and carotenoids were measured before and after the trial, and their expectations about the benefits of eating more fruits and vegetables were measured after the trial.
Compared with the control group, test group #2 (people actively given fruits and vegetables) displayed improvements in psychological well-being and increases in "vitality, flourishing, and motivation". Interestingly, the benefits were not linked to increases in blood levels of vitamin C or carotenoids, or to the participants' expectations.
However, no diet-related changes were found for depressive symptoms, anxiety, or mood.
As the researchers wrote, “We conclude that providing young adults with high-quality [fruits and vegetables] FV, rather than reminding them to eat more FV (with a voucher to purchase FV), resulted in significant short-term improvements to their psychological well-being. These results provide initial proof-of-concept that giving young adults fresh fruit and vegetables to eat can have psychological benefits even over a brief period of time.”
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