The goal of this clinical trial is to determine if a high potassium intake can counteract the harmful effects of excess sodium on endothelial function in older adults with no history of cardiometabolic disease. The main questions it aims to answer are:

1. Can a high potassium intake attenuate dietary sodium-induced endothelial dysfunction in older adults.
2. Do changes in endothelial function in response to alterations in sodium and potassium intake differ by sex.

Participants will participants will consume three controlled diets for 10 days each with a minimum 14-day washout between interventions. The order in which participants consume the diets will be randomized. The study diets will vary in sodium and potassium content. Measures of cardiovascular health (blood pressure, arterial stiffness, endothelial function) will be assessed at the end of each diet.

Cardiovascular health declines with age, especially in postmenopausal females. High sodium diets are a major contributor to cardiovascular disease. Unfortunately, reducing sodium intake can be challenging. It is known that increasing potassium intake can improve cardiovascular disease risk factors in young adults, even if sodium intake remains high. The investigators are hoping to show that potassium can improve cardiovascular health in the context of a high sodium diets in older adults. In this study, participants will consume three 10-day controlled diets in a randomized order. The study diets will include: 1) a low sodium (2,000 mg/day)/low potassium (2,000 mg/day) diet; 2) a high sodium (4,700 mg/day)/usual potassium diet; and 3) a high sodium/high potassium (4,700 mg/day). All food will be provided to participants during these periods, and participants will be instructed not to consume any outside food or beverages. Dietary interventions will be separated by a minimum two-week washout period. Measurements of cardiovascular health will be collected at the end of each diet.

Inclusion Criteria:

• Adults ages 55-75 years
• At least one-year post-menopause (females)
• Willing and able to attend laboratory visits

Exclusion Criteria:

• BMI ≥35 kg/m2
• Seated blood pressure >135/85 mmHg
• Current diagnosis or history of cardiovascular disease, diabetes, renal disease, cancer, or major cardiovascular event (e.g. heart attack or stroke)
• Taking exogenous hormones or hormone replacement therapy
• Following a vegan or gluten free diet
• Significant weight loss (>10% of body weight) in the last 6 months, or actively trying to lose weight
• Current or recent use of a diuretic (within the past 6 months) (e.g. spironolactone, eplerenone)
• Current or recent use of a potassium binding medication (within the past 6 months)
• Current use of blood pressure lowering medications (e.g. ACE inhibitors, calcium channel blockers, diuretics, vasodilators, beta blockers, AngII receptor blockers)
• Current or recent use of the medication trimethoprim
• Elevated blood lipids (LDL cholesterol ≥190 mg/dL)
• Elevated serum potassium level (>5.1 mmol/L)
• Elevated BUN (>22 mg/dL)
• Elevated creatinine (>1.2 mg/dL)
• Low eGFR (<90 mL/min/1.73 m²)
• Current or recent use of tobacco, nicotine, or illicit drugs
• Radical hysterectomy or oophorectomy (females)