Background: Low-carbohydrate diets decrease hemoglobin A1c among patients with type 2 diabetes mellitus. However, evidence on effects of low-carbohydrate diets on hemoglobin A1c among individuals with prediabetes is limited.

Methods: We conducted a randomized parallel-group trial of 150 adults aged 40-70 years with untreated hemoglobin A1c from 6.0-6.9%. Participants were assigned to a healthy low-carbohydrate diet (target <40 grams net carbohydrates months 1-3; <60 grams months 3-6) or usual diet. The low-carbohydrate arm received regular dietary counseling. Data on hemoglobin A1c and other metabolic risk factors were collected at 0, 3, and 6 months.

Results: Mean age was 59 years; 72% were female and 59% were Black. 95% completed the study. Participants in the low-carbohydrate arm had significantly greater 6-month decrease in hemoglobin A1c (net difference, -0.23% [95% CI, -0.32 to -0.14%]) , fasting plasma glucose (net difference, -10.3 mg/dL [95% CI, -15.7 to -4.9 mg/dL]) , and body weight (net difference, -5.9 kg [95% CI, -7.2 to -4.7 kg]) compared with usual diet arm. At 6 months, 53% in the low-carbohydrate arm and 32% in the usual diet arm had hemoglobin A1c <6.0% (p=0.01) .

Conclusion: A healthy low-carbohydrate diet led to improvements in glycemic and other cardiometabolic outcomes in adults with elevated hemoglobin A1c and could be recommended for prevention of type 2 diabetes mellitus.


K.S.Dorans: None. M.J.O'brien: None. G.I.Uwaifo: None. J.He: None. L.A.Bazzano: None. L.Qi: None. H.He: None. J.Chen: None. L.J.Appel: n/a. F.Hu: None. J.Samet: None. K.T.Mills: None.


National Institute of General Medical Sciences (1P20GM109036-01A1) . The California Walnut Commission (Folsom, CA) supported the study by providing walnuts. Shakes and bars were donated by The Simply Good Foods Company (Denver, CO) . Sugar replacement samples were provided by Swerve LLC (New Orleans, LA) .

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