Chronic effects of isoflavones on cognition and aggression in a female population across the menstrual cycle.

INTERVENTION: Capsule containing 200 mg isoflavones (SoyLife 40) taken once daily for two menstrual cycles. Participants were asked to return unused capsules at each study visit in order for compliance to be monitored. CONDITION: Aggression Cognitive function Mood Premenstrual syndrome PRIMARY OUTCOME: Aggression measured using the Buss‐Perry Aggression Questionnaire (BPAQ). SECONDARY OUTCOME: Aggression measured using the state‐trait anger expression inventory (STAXI) and an emotional Stroop task. Anxiety measured using the State‐Trait Anxiety Inventory. Brain electrical activity during a standard and an emotional go/no‐go task measured using electroencephalography (EEG). Cognitive function assessed using the COMPASS cognitive testing battery. The domains of working memory, executive function, secondary memory, attention and reaction time were assessed using the following tasks: immediate and delayed word recall; word recognition; picture recognition; corsi blocks forward and reversed; N‐back; alphabetic and numeric working memory; simple, choice and four choice reaction time; sentence verification; peg and ball; card sorting; rapid visual information processing (RVIP); serial subtractions. Depression measured using the Beck Depression Inventory. General mood measured using the Profile of Mood States. General physical and psychological symptoms measured using the Symptom Checklist. Impulsivity measured using the Barratt Impulsiveness Scale. Premenstrual symptoms measured using the Revised Daily Symptom Report (DSR‐20). Schizotypal personality traits measured using the Schizotypal Personality Questionnaire. INCLUSION CRITERIA: Aged 18‐35 Regular menstrual cycles Using no hormonal contraception for past 3 months (or using combined oral contraceptive pill for at least 3 months if in the positive control group) BMI between 19 and 26 Consume soy products less than 2 times per week Non‐smoker Not seeking help for premenstrual syndrome Not pregnant or lactating No history of psychiatric disorders, anxiety or depression No neurological, gastrointestinal, endocrine or bleeding disorders No food allergies or intolerances