Effect of Walnuts on Cognitive Function and Gut Microbiome in Older Adults

Inclusion Criteria: * Age 55 years or older * Able to hear well enough to understand spoken instructions and questions * Able to see well enough to read and respond to printed instructions and fill out questionnaires (corrective lenses are allowed) * Able to write legibly and move a computer joystick with at least one hand (i.e., no injury or connective tissue or joint disorder that would impair ability to write or make hand movements) * Able to speak, read, and understand English * Score of greater than 79 on water maze learning task * Willing to maintain current eating patterns * Willing and able to complete the cognitive tests * Willing to stop consuming almonds, Brazil nuts, cashews, chestnuts, hazelnuts, macadamia nuts, peanuts, pecans, pistachios, walnuts, persimmons and pomegranates for 14 weeks. - are nuts or contain ellagitannins or ellagic acid - compounds/foods of interest for this study * Willing to limit oak aged wines and spirits to 1 serving/day and limit blackberries (including similar berries like boysenberries, marionberries, and olallieberries), cloudberries, cranberries, currants, elderberries, lingonberries, raspberries, strawberries, wolfberries, other native berries; guava, mango, muscadine grapes, nectarines, peaches, plums, pluots to 1 cup/day for 14 weeks; REMAIN CONSISTENT (consistent intake levels of): Coffee, tea, apple, apricots, blueberries, cherries, grapes (table/common) * Willing to stop probiotic supplements 2 weeks prior to and during the study (14 weeks) Exclusion Criteria: * Consumption of walnuts, pecans, and chestnuts combined greater than 2 oz / week in the past 3 months. * Use of oral antibiotics in the past month * Regular use of oral anti-inflammatory medications in the past month * Nut, wheat, or gluten allergy/intolerance * Pregnant or planning to become pregnant during the study period * Weighs less than 110 pounds * Diagnosis of sickle cell disease * Susceptibility to motion sickness * Consumes 3 or more alcoholic drinks daily * History of smoking tobacco products, including e-cigarettes and vaporizers in the past 2 years (smokeless tobacco use not exclusionary) * Use of psilocybin or cannabis products (including CBD-only products) in the past 2 years * Current treatment for alcohol or other substance use disorder * History of heart attack, heart failure, or stroke, including transient ischemic attack * History of liver disease or kidney disease requiring dialysis * History of cancer in the past 5 years (Skin cancer that was only surgically treated is not exclusionary) * History of bariatric surgery (e.g., gastric bypass, gastric banding, sleeve gastrectomy, etc.) or disorders (e.g., Crohn's disease, unmanaged celiac disease, ulcerative colitis) * History of thyroid disorder that requires medication, but subject is not taking medication * History of chronic bronchitis or emphysema * Diagnosis of dementia or Alzheimer's disease * History of head injury requiring hospitalization or loss of consciousness \> 5 minutes * History of chronic migraines (for at least 3 months, headache occurring on 15 or more days per month, where at least 8 of those headache days have migraine symptoms) * Blood pressure above 159 (systolic) or 99 (diastolic) mm Hg * Corrected vision worse than 20/50 * Score of less than 10/15 on Ishihara color vision test or diagnosis of color blindness * Score of less than 26/30 on Mini-Mental State Exam * Score of greater than 15 on Center for Epidemiologic Depression survey * History of disease or disorder which causes cognitive impairment, including but limited to: attention-deficit/hyperactivity disorder (ADHD), amyotrophic lateral sclerosis, autism, bipolar disorder, Down's syndrome, encephalitis, epilepsy/seizures, human immunodeficiency virus (HIV), Huntington's disease, Korsakoff's psychosis, multiple sclerosis, Parkinson's disease, or psychotic disorders (e.g., schizophrenia, schizoaffective disorder, schizophreniform disorder) * Current and regular use of any of the following medications: insulin, opioids, anti-seizure medications, psychotropic medications: stimulants, anti-psychotics, or medications that cause daytime drowsiness or difficulty concentrating