In this 3-week interventional study, the investigators hypothesize that therapeutic Time-Restricted Feeding in patients with poorly controlled Type 2 diabetes mellitus (T2DM) can improve their mean glucose or estimated glycated hemoglobin levels with the same dose, or even reduced dose, of antidiabetics.

Time-restricted feeding (TRF) has recently gained popularity as a means of reducing body weight and improving glycemia. A recent clinical trial in men who had prediabetes showed that TRF for five weeks significantly reduced fasting insulin concentration and improved the derived oral glucose tolerance test ( OGTT) indexes of beta-cell responsiveness and insulin resistance. However, the effects of TRF have not been studied in patients with poorly controlled Type 2 diabetes mellitus (T2DM). In this 3-week interventional self-controlled clinical trial, the investigators hypothesize that TRF in patients with poorly-controlled T2DM can improve their mean glucose with the same dose/reduced dose of antidiabetics. Potential study subjects will be identified from Endocrinology clinic patients with a diagnosis of poorly controlled type 2 DM (A1c >= 8.0 in the 3 months before enrollment) based on inclusion and exclusion criteria. All study subjects will be in the ad libitum feeding phase for one week, and then will be placed on time-restricted fasting (feeding between 4 AM - 4 PM, fasting in the rest of the day) for the second week. For the third and final week, patients will be returned to the ad libitum feeding phase. The first and third weeks will serve as the control phases, and the second week will be the experimental phase. The mean glucose, serum triglyceride levels, insulin resistance, and body weights will be compared between the two phases. Results of this clinical study may demonstrate a low-cost and practical way of diabetic control.

Inclusion Criteria:

• Age ≥ 18 years and < 65 years
• With the diagnosis of type 2 diabetes
• A1c >= 8.0 on the most recent test in the 3 months before enrollment
• Have been on stable antidiabetics in the 3 months before enrollment
• OhioHealth Patient

Exclusion Criteria:

• Pregnant or breastfeeding patients
• Severe hypoglycemic episodes (defined as having low blood glucose levels that requires assistance from another person to treat) in the past 12 months
• Unable to give informed consent
• Currently enrolled in another therapeutic study
• Thyroid dysfunction, as defined by abnormal thyroid function test results within the past 6 months
• Advanced stage of renal (stage 4 or above) or hepatic (cirrhosis) or respiratory (needs oxygen) or heart failure (NYHA class 3 or above)
• Active infection or malignancy
• Dementia, or other significant mental impairment that would, in the opinion of the investigator, impede patient self-reporting
• Clinician-reported history of patient non-adherence