Study partners will be instructed to assist participants in adherence to a 1:1 ketogenic diet (approximately 70% fat, <10% carbohydrate, and 20% protein as energy). The diet will encourage ≥4 servings of non-starchy vegetables and 1/2 cup of berries daily. Participants will be provided an emulsified medium chain triglyceride supplement with a target intake of 1-2 tablespoons per day and micronutrient supplements consisting of multivitamin, vitamin D, calcium, and phosphorus. After the 3-month ketogenic diet, participants will complete a 1-month washout period in which they halt adherence to the ketogenic diet and resume their normal diet.

Study partners will be instructed to assist participants in adherence to the Therapeutic Lifestyles Changes diet. The diet consists of 20-35% fat, 50-60% carbohydrate, and ~15% protein as energy. Fat intake will comprise <7% saturated fat, ≤20% monounsaturated fat, and ≤10% polyunsaturated fat as total energy. Cholesterol consumption will be ≤200mg per day. Participants are encouraged to eat ≥2 servings of fruit and ≥5 servings of vegetables per day.

Three-month 1:1 ketogenic diet intervention (approximately 70% fat, <10% carbohydrate, and 20% protein).

Cognitive performance will be assessed by a psychometrician using the Alzheimer's Disease Assessment Scale Cognitive Subscale (ADASCog11). The ADAS-Cog is an Alzheimer's disease specific, multi-domain cognitive assessment scored from 0-70 points with higher scores indicating poorer cognitive performance.

Global cognitive performance will be assessed by a psychometrician using the Mini-Mental State Exam (MMSE). The MMSE is a brief cognitive questionnaire with a maximum score of 30 points where higher scores indicate better cognitive performance.

The Logical Memory, subtest of the WMS-R is a standardized assessment of narrative episodic memory. A short story is orally presented, and the examinee is asked to recall the story immediately.

Reaction time and accuracy will be assessed by a psychometrician using the Stroop test.

The Clinical Dementia Rating is a 5-point scale (CDR 0, 0.5, 1, 2, and 3) used to characterize six domains of cognitive and functional performance applicable to Alzheimer disease and related dementias. CDR 0 indicates no dementia and higher values indicate more severe dementia. The scores of all six domains are averaged to form a global CDR score. Change in score from baseline to 3 months will be assessed.

Concentration of cerebral N-Acetylaspartate is measured using magnetic resonance spectroscopy in a 3T clinical scanner.

We will measure serum beta-hydroxybutyrate levels.

Participants will measure and report daily urinary ketone status using Ketostix (Bayer, Germany).