This is a crossover study utilizing a Dietary Approaches to Stop Hypertension (DASH) diet and a whole-food, plant-based diet among subjects with type 2 diabetes who require insulin. Outcomes are short-term changes in insulin requirements and changes in various biomarkers.

This is a single center, prospective, non-randomized crossover study. The aim of the study is to perform a comprehensive evaluation of factors that may contribute to improvements in glycemic control in obese patients with type 2 diabetes during a plant-based dietary intervention. The primary end point will be the change in total daily insulin requirements during the plant-based dietary intervention period compared against a Dietary Approaches to Stop Hypertension (DASH) diet. Evaluation of insulin requirements will be carried out in three phases of this study: pre-intervention (Phase 1), intervention (Phase 2), and post-intervention (Phase 3). Each phase is 7 days. In addition, investigators plan to evaluate the effects of a plant-based diet on glucose homeostasis by estimating the insulin sensitivity index and beta cell function using weekly sampled oral glucose tolerance tests (oGTT) and will explore if these effects correlate with changes in urinary glucose excretion by using weekly sampled urinary tests. Investigators will also be assessing changes in obesity-related inflammatory biomarkers, stress biomarkers and metabolic markers during the three phases of the study. Lastly, given the current technological advantages in the field of diabetes monitoring, investigators plan to monitor the glycemic excursion curve using a continuous glucose monitor during the complete study.

Inclusion Criteria:

• Adults (older than 18 years old) of both genders, of all races and ethnicities.
• Pre-existing diagnosis of Type 2 Diabetes Mellitus, as documented in medical records on basal with or without mealtime bolus insulin with no change to total of basal insulin and nutritional baseline insulin dosing > 10% in the 1 month prior to consent and no changes to non-insulin antihyperglycemic medications in the 3 months prior to consent
• If on a GLP-1 analog, on a stable dose for at least 3 months prior to the study enrollment
• If on an SGLT2 inhibitor, on a stable dose for at least 3 months prior to the study enrollment
• BMI of 27 kg/m2 or greater
• Most recent HbA1c (within 6 months prior to consent) between 6.5% and 9.5%
• Fluent in the English language (education about each diet will be in English)
• Willingness and ability to participate in study protocol.
• Agreeable to give informed consent.

Exclusion Criteria:

• Diagnosis of T1DM or type 1.5 diabetes mellitus
• History of liver cirrhosis
• Impaired renal function (GFR < 45 ml/min) within 6 months prior to consent
• History of hyperkalemia (potassium > 5.4 meq/L) within 6 months prior to consent
• Use of an insulin pump or expected to start during the study period
• Use of warfarin (Coumadin)
• Use of daily aspirin 500 mg or more or expected to start during the study period
• Use of daily Vitamin C of 1,000 mg or more, unless willing to stop taking 1 week prior to baseline visit and for duration of study
• Use of antipsychotics or systemic steroids within 3 months prior to consent
• Use of any of the following weight-lowering pharmacotherapy within 3 months prior to consent: phentermine, orlistat, lorcaserin, phentermine/topiramate, bupropion/naloxone
• The use of insulin secretagogues including sulfonylureas and glinides within 3 months prior to consent as this may increase the risk of hypoglycemia and alter assessment of daily insulin requirements during the study
• The use of illicit drugs, defined as active use or use within 3 months prior to consent.
• Engage in high risk alcohol use (defined as more than 4 drinks on any day or more than 14 drinks per week in men and more than 3 drinks on any day or 7 drinks per week in women).
• Individuals who are pregnant or breastfeeding or intend to become pregnant during the duration of the study
• Individuals who are following a vegetarian or vegan diet at the time of consent
• Food allergies or intolerances that will interfere with diet adherence
• Lack of access to a full-size refrigerator (required for storage of 3-4 days of prepared study meals)
• Active malabsorption disorder, including uncontrolled symptomatic inflammatory bowel disease, or bariatric surgery in the past 1 year