Long-Term Effects of Walnut Consumption on Brain Function

Inclusion Criteria: * Men and women, aged between 45-75 years * Women postmenopausal: two or more years after last menstruation * Waist circumference of ≥102 cm for men and ≥88 cm for women (abdominal obesity) * Fasting plasma glucose \< 7.0 mmol/L * Fasting serum total cholesterol \< 8.0 mmol/L * Fasting serum triacylglycerol \< 4.5 mmol/L * Systolic blood pressure \< 160 mmHg and diastolic blood pressure \< 100 mmHg * Stable body weight (weight gain or loss \< 3 kg in the past three months) * Willingness to give up being a blood donor from 8 weeks before the start of the study, during the study and for 4 weeks after completion of the study * No difficult venipuncture as evidenced during the screening visit Exclusion Criteria: * Allergy or intolerance to walnuts * Left-handedness (effects on brain function differ between left- and right-handed adults) * Current smoker, or smoking cessation \< 12 months * Diabetic patients * Familial hypercholesterolemia * Abuse of drugs * More than 3 alcoholic consumptions per day * Use of products or dietary supplements (e.g., dietary fiber or antioxidant dietary supplements (vitamin C and E), fish or seaweed oil capsules) known to interfere with the main outcomes as judged by the principal investigators * Use of medication to treat blood pressure, lipid, or glucose metabolism * Use of an investigational product within another biomedical intervention trial within the previous 1-month * Severe medical conditions that might interfere with the study, such as epilepsy, asthma, kidney failure or renal insufficiency, chronic obstructive pulmonary disease, inflammatory bowel diseases, auto inflammatory diseases, and rheumatoid arthritis * Active cardiovascular disease like congestive heart failure or cardiovascular event, such as an acute myocardial infarction or cerebrovascular accident * Contra-indications for MRI imaging (e.g., pacemaker, surgical clips/material in body, metal splinter in eye, claustrophobia)