The study will employ a between-groups, randomised, controlled, participant-blind design with three groups and six time points. Participants will be allocated to one of three groups; a high flavonoid condition (consumption of 2 portions of flavonoid rich food per day), low flavonoid condition (consumption of one portion of flavonoid rich food per day) and a control (no change to diet). Participants will be quasi-randomised to condition based on their baseline flavonoid intake, taken at Timepoint 1 using the European Prospective Investigation of Cancer (EPIC)-Norfolk Food Frequency Questionnaire to ensure there is an even spread of baseline flavonoid consumption in participants across all conditions. At this timepoint, participants will additionally complete the Immediate Mood Scaler. Participants will be recruited at any stage of their pregnancy though testing will not take place until their third trimester (weeks 27+). Participants will be invited to a study investigating diet mood and cognition. The study will take place in person, at participant homes over 6 time points; 1) a screening session, 2) time 1 (third trimester), 3) time 2 (after birth 0-4 days, pre intervention), 4) time 3 (mid-way through intervention \~15 days), 5) time 4 (post-intervention \~30 days) and 6) time 5 (follow up, 12 weeks postpartum).

Interested participants will be invited to an in-person screening session. Once participants have consented to taking part, they will be asked to provide some demographic information (e.g. age, occupation, health or psychological diagnosis). Participants will then complete practice versions of the cognitive tests. At each timepoint, the experimenter will visit participants to complete outcome measures (PANAS-NOW, EPDS, PSAS, STAI, EPDS-P, MANT, Spatial n-back, RAVLT and PRMQ, Systolic and Diastolic blood pressure). Over the course of the study, participants will be contacted at nine random timepoints to complete retrospective 24hr food recalls using the software Intake24.

Participants in the flavonoid intervention groups will be contacted by the researcher shortly before time 2 where they will be sent a list of the intervention foods and asked to choose a food item which the researcher will bring to the testing session. This is to ensure that participants can start the intervention after the testing session at time 2 without needing to visit a supermarket during this sensitive time. During this session, participants will also be asked some questions about the baby and birth experience (e.g. how old their infant is, infants sex, mode of delivery, birth complications). After the outcome measures have been taken, participants will be informed of their condition and instructed to begin the intervention. The two intervention groups will also be asked to keep a food log of their selected intervention foods for the 30-day period.

At the final timepoint, upon completion of outcome measures, participants will receive the debrief document and they will receive information about payment and dietary assessment via email. Participants will also be reminded of their right to withdraw their data from the study if they wish. Helplines and support web links will be provided to all participants as well as encouragement for participants to contact their General Practitioner should they wish to seek support. Helplines and weblinks include Samaritans United Kingdom and PANDAS Foundation. Weblinks to National Health Service (NHS), MIND mental health charity and the Association for Postnatal Illness.