The study team is studying how increasing dietary fiber, specifically through adding potato starch to participant's diet, may impact the species of bacteria in participant's gut microbiome. The study team also wants to understand if adding potato starch to participant's diet helps these bacteria make more short chain fatty acids, a byproduct the team thinks may benefit participant's health.

Inclusion Criteria:

• A confirmed clinical diagnosis of stable HFpEF on maximally tolerated Heart Failure (HF) medical regimen (without changes in dosage in the prior month)
• Left ventricular ejection fraction of >50% documented in the prior 12 months
• A confirmed clinical diagnosis of Type II diabetes (T2DM) with glycated hemoglobin <10% without changes in medical regimen in the past month.

Exclusion Criteria:

• Current usage of pre- or probiotic usage
• Antibiotic usage in the past 6 months
• Current participation in another interventional clinical trial
• History of potato allergy or potato starch allergy, inflammatory bowel syndrome, inflammatory bowel disease, bowel resection, Roux-en-Y gastric bypass surgery, celiac disease, Crohn's disease, or colorectal cancer
• Hypoglycemic episode with blood glucose 70 milligrams per deciliter (mg/dL) within the last month
• Stage IV-V chronic kidney disease
• Pregnancy (self-reported)
• Comorbidity limiting survival to < 12 months