This is a randomized trial with a crossover design to investigate the short-term effects of two different dietary patterns on markers of vascular health. A low-carbohydrate diet and a whole-food, plant-based diet will be used. In addition to more traditional markers (cholesterol, blood pressure, inflammation), endothelial progenitor cells and trimethylamine N-oxide will be assessed.

This study is an investigation of the short-term effects of two different diets on both conventional as well as newer markers of vascular health among subjects over the age of 50 who have a cardiovascular risk factor. The low-carbohydrate diet will be consistent with low-carbohydrate diet maintenance plans, with "net" carbs kept under 50g per day. The whole-food, plant-based diet will exclude animal foods, oils, and solid fats. Meals will be provided, and subjects will consume each diet for 2 weeks, with a 4-6 week washout period between dietary phases. Subjects will be randomized 1:1 to start with either the plant-based diet or the low-carbohydrate diet. Its primary aim is to assess the short-term effect of a whole-food, plant-based diet and a low-carbohydrate diet on levels of endothelial progenitor cells and trimethylamine N-oxide among this population. Secondarily, we will assess more conventional measures of vascular risk, including cholesterol, weight, blood pressure, insulin resistance, and inflammatory marker, as well as fullness and changes in nutritional intake.

Inclusion Criteria:

• Age >50
• Diagnosis of any of the following cardiovascular risk factors: hypertension (Diagnosis present in chart or use of antihypertensive medications); hyperlipidemia/dyslipidemia (non-HDL cholesterol ≥ 130 within the past year or current use of antihyperlipidemic medication); prediabetes (HbA1c ≥ 5.7% and < 6.5% in the past year); diabetes (HbA1c ≥ 6.5% in the past year); obesity (body mass index ≥ 30).
• Willing and able to comply with the protocol for the duration of the study, including food provision, scheduled meetings and testing visits.
• Able to speak and read English fluently because counseling and education is only available in English.

Exclusion Criteria:

• Active malabsorption syndrome (celiac disease, history of gastric bypass within the past year, uncontrolled Crohn's disease, protein-losing enteropathy, etc…)
• Use of any of the following medications that require close monitoring and adjustment during major dietary change: insulin, sulfonylureas, or warfarin
• Chronic or acute kidney disease, with eGFR < 50 on two or more lab tests in the past 6 months
• Diagnosis of cirrhosis or liver failure
• Hyperkalemia (defined as potassium >5.4 on two or more lab tests in the past 6 months)
• Major surgery in the past 3 months
• Myocardial infarction in the past 6 months
• Current, active eating disorder as determined by chart review, investigator assessment, or subject history
• Food allergies or intolerances that would interfere with eating study food or require special accommodation as determined by subject history, investigator assessment, or chart review
• Consuming a current diet described by the subject as vegetarian, vegan, very low-carbohydrate, or ketogenic
• Illicit drug use (not including marijuana)
• High risk alcohol use, based on subject history (defined as greater than 7 drinks/week for women and greater than 14 drinks/week for men)

Laboratory personnel will not know which dietary phase each subject has completed, but otherwise blinding is not possible.