University of Wisconsin–Madison Medical College of Wisconsin

Feasibility Study of a Low-Carbohydrate/Time-Restricted Eating Protocol for Insulin-Using Type 2 Diabetic Patients

Philip N. Zimmermann, MD; Linda M. Baier Manwell, MS; Fauzia Osman, MPH; David Feldstein, MD

WMJ. 2024;123(1):11-17.

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Introduction: Low-carbohydrate diets and time-restricted eating are methods to improve hemoglobin A1C in patients with type 2 diabetes. However, insulin-using patients are often counseled against these practices due to hypoglycemia concerns. This observational study evaluated a protocol utilizing both methods coupled with proactive insulin titration.

Objectives: To evaluate the safety and feasibility of a timed eating protocol for insulin-using patients and to assess its impact on outcomes, including insulin use and hemoglobin A1C.

Methods: Participants included insulin-using adults ages 49 to 77 years with type 2 diabetes. They were counseled to eat 2 meals per day in a 6- to 8-hour window of their choosing, with a goal intake of ≤ 30 grams of carbohydrates per day. Glucose was closely monitored, and insulin was adjusted per study protocol. Primary outcomes included hypoglycemic events and compliance with timed eating. Insulin use, hemoglobin A1C, body mass index, blood pressure, and quality of life also were measured.

Results: Nineteen of the 20 participants completed the 6-month study. No hypoglycemic events requiring urgent medical care occurred. Symptomatic episodes with glucose between 47 and 80 mg/dl were reported by 37% (7/19) of participants. Average daily insulin use decreased by 62.2 U (P < 0.001) and insulin was discontinued for 14 participants. Average hemoglobin A1C remained unchanged. Average body mass index decreased by 4.0 (P = 0.01), systolic blood pressure decreased by 9.9 mm Hg (P = 0.02), and diabetes-related quality-of-life metrics improved significantly.

Conclusions: These results demonstrate that a time-restricted eating protocol is feasible and safe for insulin-using patients with type 2 diabetes when paired with a proactive insulin titration.

Author Affiliations: Division of General Internal Medicine, Department of Medicine, University of Wisconsin (UW) School of Medicine and Public Health (SMPH), Madison, Wisconsin (Zimmermann, Baier Manwell, Feldstein); Department of Medicine, UW SMPH, Madison, Wis (Osman).
Corresponding Author: Philip Zimmermann, MD, General Internal Medicine Clinic, Room 405, 20 S Park St. Madison, WI 53715; phone 608.287.2250; email to
Funding/Support: This work was supported by a University of Wisconsin- Madison Division of General Internal Medicine Pilot Grant Award.
Financial Disclosures: None declared.
Acknowledgements: The authors wish to acknowledge Alisa Sunness, RD, CD, CDE, and Schyler Arthur, RN whose contributions made this study feasible.
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