New psychology findings offer evidence that the food we eat has a direct influence on our mental health. The study, published in the British Journal of Nutrition, found that eating more fruit predicted fewer depression symptoms and greater psychological well-being while eating more savory snacks predicted increased anxiety.
In recent years, scientists have begun to consider whether modifying one’s diet might offer a pathway to improving psychological health. This idea comes on the heels of evidence linking the consumption of nutrient-dense foods (e.g., fruits and vegetables) to fewer mental health issues, and the consumption of nutrient-poor foods (e.g., candies, savory snacks) to worse stress, anxiety, and depression.
It is unclear why diet might impact mental health, but study author Nicola-Jayne Tuck and her team say it may have to do with the way nutrients impact our cognitive processes. Past studies have suggested that a nutrient-poor diet negatively impacts cognitive function while a nutrient-rich diet improves it. And cognitive deficits, such as reduced inhibitory control and cognitive failures, have been associated with worse mental health.
Tuck and her colleagues conducted a study to explore whether diet might influence mental health through its impact on cognition, while also investigating the impact of both the frequency and quantity of fruit and vegetable consumption.
A nationally representative sample of 428 UK residents completed an online survey that assessed their dietary habits, psychological health, and cognitive function. Participants were asked to indicate how frequently they consumed fruits, vegetables, sweet snacks (e.g., cakes, cookies), and savory snacks (e.g., potato chips) per day in the past month, and how many portions of fruits and vegetables they ate per day. They further completed assessments of depression, anxiety, stress, and psychological well-being. To control for possible covariates, participants completed certain health-related measures that included smoking, alcohol, and exercise habits.
The subjects additionally completed a self-report cognitive failures questionnaire that assessed “attentional, memory, perceptual and action-related mental lapses in everyday tasks” in the past 6 months (e.g., forgetting appointments, dropping things). Participants then completed the Stop-Signal Task as a behavioral measure of cognitive control.
The results revealed that, after controlling for covariates, frequency of fruit intake (but not quantity of fruit intake) positively predicted psychological well-being and negatively predicted depression. While additional experimental data is needed, the study authors speculate that, “how often we consume fruit may be more important than the total amount we consume.”
Consuming savory snacks (but not sweet snacks) positively predicted anxiety. This is in line with past research suggesting that salty food and fast food can increase anxiety. Notably, the study was cross-sectional, making the direction of this relationship unclear. It could be that people with higher stress and anxiety eat more nutrient-poor foods as a coping strategy.
The results further revealed that the link between savory snacking and mental health was mediated by cognitive failures. In other words, participants who consumed savory snacks reported more cognitive failures, and in turn, higher symptoms of depression, anxiety and stress, and lower well-being. Given that animal studies have suggested that saturated fats can reduce memory function, it may be that savory snack foods that are high in saturated fat can impair memory and, in turn, mental health.
Interestingly, the frequency of vegetable intake did not impact mental health after controlling for covariates. The researchers say this may be because the vegetables people eat are often canned and cooked, which might limit the absorption of nutrients. Fruits, on the other hand, tend to be consumed raw.
Overall, the findings suggest that adjusting one’s intake of nutrient-poor (processed) and nutrient-dense (unprocessed) foods may help protect mental health. “Further work is now required to establish causality,” Tuck and her colleagues say, “and determine whether these may represent modifiable dietary targets that can directly (and indirectly) influence our psychological health.”
The study, “Frequency of fruit consumption and savoury snacking predict psychological health; selective mediation via cognitive failures”, was authored by Nicola-Jayne Tuck, Claire V. Farrow, and Jason Michael Thomas.
