“Lettuce be happy”: Fruit and vegetables boost mental health, says UK study

20 Feb 2019 --- The daily consumption of fruit and vegetables is not just good for our physical health but can also improve mental wellbeing, according to a longitudinal study from the University of Leeds, UK. Increasing the frequency and quantity of consumption may also affect mental health. Although the association between mental health and fruit and vegetable intake appears to be strong, the researchers note more research is needed to determine whether this is causal.

The researchers combined the results of a previous Australian study with data from the UK Household Longitudinal study – which involves more than 40,000 UK households – to determine if there is a correlation between the consumption of fruit and vegetables alongside psychological improvements.

“The results were largely in line with a 2016 study on Australian data by Mujcic and Oswald, as well as other smaller scale studies. As such, they were not completely surprising, but it was still encouraging to see the relationship reproduced in the large UK panel data we had,” Dr. Neel Ocean, lead author and Research Fellow in Behavioural Economics at Leeds University, tells NutritionInsight.

Published in Social Science and Medicine, the study employed panel data analytical techniques collected between 2010 and 2017. “We controlled for a variety of demographic factors including age, income, marital status, employment status and education, as well as lifestyle variables such as smoking and  The frequency of fruit and vegetable consumption in a typical week, separated by age band (n = 130,540 for fruit; n = 130,550 for vegetables).walking. The relationship we found remained after we accounted for all of these variables,” Ocean explains.

According to the study, there was no connection between overall physiological health and mental wellbeing. The researchers were able to control for both general health and the presence of a longstanding health condition and found no link. “The positive relationship with mental wellbeing holds even when we take health into account,” Ocean adds. 

Quantity and frequency of consumption also play a part in improving mental wellbeing, and since most people do not consume their recommended five portions of fruit and vegetables a day, Ocean says that adding one portion per day could significantly improve psychological health.

Consumption of vitamins C and E seems to be important for mental health, according to the researchers, who also controlled on bread and dairy products and found that “these do not appear to be related to mental wellbeing.”

Ocean says that the exact mechanisms behind the positive relationship between fruit and vegetable consumption and mental wellbeing are yet unknown and there are no rules to follow in terms of food formulation that will boost mental health.

“However, it probably wouldn’t be a bad thing if there was an increase in the availability of convenience foods that had significant fruit or vegetable content,” he notes.

“In further longitudinal work, ideally, one’s entire diet needs to be accounted for so that we can rule out other explanations that relate to overall calorie intake or the consumption of other foods (the availability of data is usually the limitation here),” Ocean says. 

“A large-scale randomized controlled trial testing the well-being effects of a fruit and vegetable intervention would help to determine whether the relationship was causal,” Ocean concludes.

While more research is certainly warranted, the importance of a healthy diet rich in fruit and vegetables has long been known. At the same time, a growing body of evidence links processed foods, saturated fats and sugar to mental health issues such as depression and anxiety.

Another study found that adolescent rats that consume a diet high in saturated fats are at an increased risk of psychopathology in adulthood. Moreover, the researchers from Loma Linda University in California found that the areas of the brain that handle fear or stress responses were altered to the point that subjects began exhibiting behaviors that mirror post-traumatic stress disorder (PTSD).

The importance of the gut-brain axis is also still being explored with research recently establishing a correlation between depression and a group of neurotransmitter-producing bacteria found in the human gut. Interestingly, an inverse relationship between specific gut bacteria and brain activity in areas connected to depression were identified in the animal study. Published in Nature Microbiology, the findings could lead to the development of bacterial therapeutics for depression, including a growing role for probiotics.

By Kristiana Lalou