February 14, 2019
The physical benefits of eating fruits and vegetables are well documented, but new research shows that higher consumption of these foods also improves mental health and well-being.
Results of a large longitudinal study in the United Kingdom show that when individuals increased their fruit and vegetable consumption, their short-term mental well-being — as measured by the 12-item General Health Questionnaire (GHQ-12) — also increased.
These findings, say investigators, provide yet more evidence that persuading people to consume more fruits and vegetables may not only bolster long-term physical health but also boost mental health.
"Our paper has verified a longitudinal relationship found in a large Australian [study] in an even larger UK sample, with results that are very close," principal investigator Neel Ocean, PhD, University of Leeds, United Kingdom, told Medscape Medical News.
"This adds robustness to the positive relationship between fruit and vegetable consumption and mental well-being, shows that it isn't isolated to just one country, though there are, of course, cultural similarities between the two countries, and sets the scene for further research surrounding the precise mechanisms that are involved in this relationship," Ocean added.
The study was published online January 7 in Social Science and Medicine.
Let Them Eat Fruit!
In addition to the well-documented benefits of fruit and vegetable consumption for physical health, recent research has begun to shine light on potential advantages with respect to mental and subjective well-being as well. In 2013, David G. Blanchflower, PhD, and colleagues demonstrated a positive association between eating fruits and vegetables and psychological well-being.
In 2017, in a study entitled "Let Them Eat Fruit! The Effect of Fruit and Vegetable Consumption on Psychological Well-being in Young Adults," Tamlin S. Conner, PhD, and colleagues offered a more controlled look at the subject. In that trial, young adults in the treatment group received two additional portions of fruit and vegetables each day over a 2-week period.
Results showed that individuals who received the extra fruits and vegetables experienced significantly improved psychological outcomes than did those who did not receive the extra portions.
However, said Ocean, although such previous research is compelling, much of it has relied on cross-sectional correlations, convenience samples, or a lack of adequate controls.
Given such shortcomings, the investigators turned to data from the UK Household Longitudinal Study, which provided data from more than 40,000 participants.
The longitudinal nature of that survey allowed the researchers to relate any changes in participants' fruit and vegetable consumption to changes in their well-being over time.
In addition to using a subjective life-satisfaction tool similar to those employed in previous studies, the current team of investigators applied the GHQ-12 as a measure of mental well-being.
Panel-data analytic techniques were employed on the three waves of participant data, which were collected between 2010 and 2017. The researchers also controlled for alternative factors that may affect mental well-being, such as diet, health, and lifestyle behaviors. Food-related behaviors, such as bread and dairy-product consumption, were added as controls.
Perhaps not surprisingly, the analysis revealed that the majority of people in the database consumed fewer than the often recommended benchmark of five portions of fruits and vegetables each day.
This finding, they note, is largely consistent with those from a 2016 Australian study, which found that 85% of participants consumed fewer than three daily portions of fruit and that 60% consumed fewer than three such portions of vegetables.
Fixed-effects regression analyses revealed that consumption of fruits and vegetables yielded a positive and statistically significant coefficient in a pooled cross-sectional model. "In other words, as the quantity of fruit and vegetables consumed increases, then so too does well-being," the investigators write.
Indeed, increasing fruit and vegetable consumption by a single portion (on a day in which at least one portion is consumed) led to a 0.133-unit increase in mental well-being (P < .01). This, the investigators note, offers the same estimated increase in mental well-being as approximately 8 extra days of walking at least 10 minutes each month.
In addition to examining the impact of the quantity of consumed fruits and vegetables on mental well-being, the investigators also analyzed the relationship between well-being and the frequency of fruit and vegetable consumption in a typical week.
This analysis yielded similar results: the more often fruits and vegetables were consumed by participants each week, the higher their mental well-being was likely to be.
To help check the robustness of their findings regarding mental well-being, the investigators repeated their analyses using self-reported life satisfaction as the dependent variable. These analyses revealed similar results: the quantity and frequency of fruit and vegetable consumption had a significant and positive relationship with life satisfaction.
Ocean and colleagues indicate that findings such as these offer simple ways to improve mental health.
"[W]hen it comes to improving mental health, policies aimed at increasing fruit and vegetable consumption among the general population may provide a relatively low-cost public health intervention that supplements current approaches (generally involving pharmaceuticals and/or cognitive behavioral therapy)," they write.
Good for the Body, Good for the Brain
Commenting on the findings for Medscape Medical News, Natalie Parletta, PhD, from the University of South Australia, Adelaide, was encouraged to see that a longitudinal study backs up what correlational studies have been reporting for years.
"Mental health doesn't exist in a silo," said Parletta, who was not involved in the study. "What is good for physical health is just as important for our mental health and well-being ... and possibly even more so.
"I hope this growing awareness will help fuel calls for people to ditch the junk food and eat more plant foods to address our scourge of modern diseases," Parletta added.
Ocean agreed that the potential for improving mental and physical health may motivate people to add more fruits and vegetables to their diets.
"As an intervention, it is relatively low cost and easy to achieve. It would be interesting to see whether governments and/or health services can conduct further trials with dietary interventions that specifically increase fruit and vegetable intake, in order to see if there is a causal link," said Ocean.
The study was funded through the Global Food Security's Resilience of the UK Food System Programme, with support from the UK Biotechnology and Biological Sciences Research Council, the UK Economic and Social Research Council, the UK National Environment Research Council, and the Scottish Government.