Peanut butter at breakfast may tame blood sugar and sharpen the mind

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Age 40-65 years * BMI 25 to 40 kg/m2 * HbA1c 5.7-6.4% * Low habitual intake of peanut butter (\<0.5 Tablespoons/day on average) * Have a smartphone device or be willing to use one provided by the study Exclusion Criteria: * Hemoglobin \<13.2 g/dL for men or \< 11.7 g/dL for women at screening * Fasting triglycerides \>350 mg/dL at screening * LDL-cholesterol ≥190 mg/dL assessed by the Martin-Hopkins equation at screening * ≥10% change in body weight within the 6 months prior to enrollment * Blood pressure \>140/90 mmHg at screening * Diagnosed type 1 or type 2 diabetes * Takes any (prescription or over-the-counter) anti-hypertensive, lipid-lowering, glucose-lowering or body weight altering drugs * Intake of supplements that affect the outcomes of interest (i.e., lipids, blood pressure, glucose, body weight, and microbiome) and are unwilling to cease during the study period. * Unwilling to refrain from starting to take any supplements, vitamins, nutritional products, or health foods that are not prescribed by a doctor for the duration of the study * Self-reported history of diagnosed liver, kidney, or autoimmune disease * Self-reported history of a prior cardiovascular event (e.g., stroke, heart attack) * Self-reported history of diagnosed neurological disease (e.g. Alzheimer's Disease, Parkinson's Disease, Multiple Sclerosis) * Current pregnancy or intention of pregnancy within the next 12 months * Lactation within the prior 6 months * Peanut allergy/intolerance/sensitivity/dislike * Antibiotic use within the prior four weeks * Oral steroid use within the prior four weeks * Use of tobacco or nicotine-containing products within the past 6 months * History of cancer at any site within the past 10 years (eligible if ≥10 years without recurrence) or non-melanoma skin cancer within the past 5 years (eligible if ≥5 years without recurrence) * Participation in another clinical trial within 60 days of baseline * Currently following a restricted or weight-loss diet * Prior bariatric surgery * Intake of \>14 alcoholic drinks/week and/or not willing to avoid alcohol consumption for 48 hours prior to test visits * Does not speak and/or understand English * Unwilling to refrain from donating blood and/or plasma during the study * Weight \<110 lb * Unwilling to contact study staff before enrolling in other health-related research and avoid participating in any research that may interfere with this study * For individuals taking thyroid medication: abnormal thyroid stimulated hormone (TSH) concentration, or change in dose of thyroid medication within the last 6 months * Principal Investigator discretion related to the potential participant's ability to adhere to the study requirements, including being able to come to attend visits