Low-carbohydrate Diet Could Help Improve Untreated HbA1c of 6.0% to 6.9%

Among adults with prediabetes and untreated diabetes, following a low-carbohydrate diet led to a significant decrease in hyperglycemia, fasting plasma glucose, and body weight at 6 months, according to research from investigators at Tulane University.

The study authors, writing in JAMA Network Open, say the findings suggest “that a low-carbohydrate diet, if sustained, might be a useful dietary approach for preventing and treating type 2 diabetes,” but caution that additional research is needed.

As context for their research the investigators, led by Kirsten Dorans, ScD, assistant professor of epidemiology at Tulane University School of Public Health and Tropical Medicine, first cite the large body of evidence that supports the role of diet in type 2 diabetes prevention and management, with the majority of interventions prescribing reduced caloric and total fat intake. Other research has found adherence to low carbohydrate meal planning equally aseffective as low-fat diets for weight loss and improving cardiovascular risk. Finally, they add, there is evidence to suggest that larger restrictions in carbohydrate intake are associated with commensurate decreases in HbA1c in persons with T2D.

However, there is scant research, according to Dorans et al, exploring the effect of carbohydrate restriction on HbA1c and metabolic risk factors among adults with prediabetes or with diabetes but not on medication.

To begin to fill this void, Dorans and colleagues conducted a randomized clinical trial comparing the effect of a low carbohydrate diet intervention with a usual diet on 6-month changes in HbA1c among adults with untreated HbA1c of 6.0% to 6.9%.

There is scant research exploring the effect of carbohydrate restriction on HbA1c and metabolic risk factors among adults with prediabetes or with diabetes but not on medication.

Study participants were adults aged 40 to 70 years recruited from an academic medical center in New Orleans, LA, between September 2018 and June 2021. Persons using antihyperglycemic medication or with type 1 diabetes were excluded.

Per trial protocol, participants randomized to a low-carbohydrate diet intervention had a daily target of <40 net grams of carbohydrates during the first 3 months and <60 net grams for months 3-6. The group received dietary guidelines and also individual and small group behavioral counseling throughout the study. The usual diet group received standard dietary advice and was offered optional monthly education sessions on unrelated topics.

FINDINGS

Researchers identified 2722 participants for potential study inclusion of which 962 were screened and a total of 150 were randomized equally to the low-carbohydrate dietary intervention or to the usual diet intervention.

Mean age of the cohort was 58.9 (SD, 7.9) years, 72% were women, and 59% were Black. Baseline mean HbA1c among the 150 participants was 6.16% (SD, 0.30%); 130 participants (87%) had untreated HbA1c <6.5%. At baseline, mean body mass index (BMI) was 35.9 kg/m2 (6.7). At the 6-month analysis, data were collected for 142 (95%) participants.

Dorans et al report that adherence to the low-carbohydrate dietary intervention was associated with significantly greater reductions at 6 months in HbA1c (net difference, –0.23% [95% CI, –0.32% to –0.14%]; P <.001), fasting plasma glucose (–10.3 mg/dL [95% CI, –15.6 to –4.9 mg/dL]; P <.001), and body weight (–5.9 kg [95% CI, –7.4 to –4.4 kg]; P <.001) compared to adherence to usual diet.

There were also significantly greater 6-month decreases in the low carbohydrate vs the usual diet group for exploratory outcomes, including fasting insulin, HOMA-IR, and waist circumference, according to the study. For diastolic blood pressure and HDL-C, there were no significant differences in 6-month changes.

The researchers note that while the mean observed reduction in HbA1c of 0.23% appears modest, a similar reduction of 0.17% in HbA1c was seen at 6 months “in the lifestyle compared with control group in the landmark Diabetes Prevention Program (DPP) trial. The DPP promoted a low-fat, low-calorie diet, moderate activity, and weight loss and yielded a 58% T2D risk reduction over an average of 2.8 years."

“This dietary approach may be an option for people with or at high risk of T2D to improve glycemic and other markers and should be studied further and over longer time periods in other populations and settings.”

Reference: Dorans KS, Bazzano LA, Qi L, et al. Effects of a low-carbohydrate dietary intervention on hemoglobin A1c: a randomized clinical trial. JAMA Network Open. 2022;5(10):e2238645. doi:10.1001/jamanetworkopen.2022.38645