Dietary intake, Cognition, and Psychological Health

Abstract

Dietary intake may be a modifiable lifestyle factor for improving psychological health. Research suggests that nutrition is associated with both mental health and psychological wellbeing. However, the independent contributions of specific dietary components including fruit and vegetable intake (frequency and quantity), or sweet and savoury snacking on a range of aspects of psychological health is yet to be established. Furthermore, cognition is a plausible psychological mechanism that may mediate this relationship. The acute effects of micronutrients in fruits on mood and affect have been measured, but the possible mood benefits of folate (a micronutrient found in vegetables) has received very little attention, and it is unclear how folate from vegetables compares to bioavailable supplementation. The aims of this thesis were to investigate the links between dietary intake and psychological health, to explore cognitive processes as a hypothetical mediator, and to examine the effects of folate on mood, affect, cognition, and psychological health. Results from the empirical studies showed that nutrient-rich fruit and vegetable consumption (separately) consistently predict symptoms of depression and positive psychological wellbeing (Chapters 3 and 4). How often fruit or vegetables are consumed may be more important than the overall quantity of intake (portions) to sustain these relationships over time. In addition, cognitive failures consistently mediated the crosssectional relationship between nutrient-poor, savoury snacking and all aspects of psychological health, which highlights everyday memory errors as a novel mechanism. Further, overall diet quality may play an indirect role via cognitive failures for reducing stress. In Chapters 5 and 6, preliminary findings suggest that precise acute effects of bioavailable folate supplementation (L-methylfolate) may exist for the reduction of negative emotional states, including anxiety, negative affect, and negative mood. This thesis emphasises the potential of dietary intake as a target for enhancing psychological wellbeing, reducing cognitive failures and poor mental health.