Low-Carbohydrate Dietary Pattern on Glycemic Outcomes Trial

The proposed randomized controlled trial will test the effect of a low-carbohydrate diet on hemoglobin A1c among individuals with elevated hemoglobin A1c that are within the range of prediabetes or diabetes. Results may provide evidence about the role of carbohydrate restriction in individuals with or at high risk of type 2 diabetes.

In the short-term, among patients with type 2 diabetes, low-to-moderate carbohydrate diets have a greater glucose-lowering effect than do high-carbohydrate diets. However, compared with usual diet, the effect of a behavioral intervention promoting a low-carbohydrate/high-unsaturated fat and high-protein dietary pattern among individuals with prediabetes or untreated type 2 diabetes is not well understood.

The overall goal of this randomized controlled trial is to study the effect of a behavioral intervention promoting a low-carbohydrate/high-unsaturated fat and high-protein dietary pattern compared with usual diet on hemoglobin A1c (HbA1c) and other metabolic risk factors among individuals with or at high risk of diabetes (HbA1c 6.0-6.9%).

A total of 150 participants with HbA1c 6.0-6.9% will be recruited and randomly assigned to either a 6-month behavioral modification program designed to reduce carbohydrate intake (initial target \<40 g digestible carbohydrates, final target \<60 g digestible carbohydrates) or to usual diet in a 1:1 randomization ratio.

The primary outcome will be the difference between the active intervention and control groups for change in HbA1c from baseline to 6 months. Secondary outcomes will be fasting glucose, systolic blood pressure, total-to-high-density lipoprotein-cholesterol ratio, and body weight.

Findings from this study may provide evidence about the role of carbohydrate restriction in individuals with or at high risk of type 2 diabetes.

Eligibility Criteria:
Inclusion Criteria:

* Men or women ages 40 to 70 years
* HbA1c 6.0-6.9%
* Willing and able to provide informed consent

Exclusion Criteria:

* Diagnosed type 1 diabetes mellitus
* Use of agents affecting glycemic control (medications for diabetes, oral glucocorticoids) within the past three months prior to enrollment
* Medical condition in which low-carbohydrate diet may not be advised: estimated glomerular filtration rate (eGFR) ≤45 mL/min/1.73 m²; self-report of liver disease due to hepatitis or alcohol; osteoporosis; untreated thyroid disease; gout; cancer (other than non-melanoma skin cancer) requiring treatment in the past year, unless prognosis is excellent
* Factors that may affect HbA1c: hemoglobin \<11 mg/dL (cutpoint for moderate-to-severe anemia, which could lead to falsely elevated or lowered HbA1c); recent blood donation or blood transfusion (self-report, past 4 months); human immunodeficiency virus (self-report)
* Self-reported history of intensive care unit stay due to Coronavirus Disease 2019 (COVID-19) in the past three months, as severe COVID-19 may affect blood glucose levels
* Allergies to nuts
* For women, current pregnancy, breastfeeding, or plans to become pregnant during the study
* Consumption of ≥21 alcoholic drinks per week or consumption of ≥6 drinks per occasion
* Current or planned residence making it difficult to meet trial requirements (due to distance from study site and/or challenges regularly traveling to site)
* Current participation in another lifestyle intervention trial or a pharmaceutical trial
* Participation of another household member in the study; employees or persons living with employees of the study
* Other concerns regarding ability to meet trial requirements, at the discretion of the principal investigator or study coordinator