Low-Carb Diet Could Improve Untreated HbA1c in People with Prediabetes, Type 2 Diabetes

Kirsten Dorans, ScD

Adherence to a low-carb diet could help improve glycemic control in people with improved elevated HbA1c not receiving glucose-lowering medications, according to a new trial from Tulane University.

A randomized clinical trial conducted in people with prediabetes and diabetes with elevated but untreated HbA1c, results of the study suggest adherence to a low-carbohydrate diet was associated with significant improvements in HbA1c, fasting plasma glucose, and body weight at 6 months compared to usual diet, but investigators caution more research is needed to understand the effects of this approach on overall health and wellbeing.

“The key message is that a low-carbohydrate diet, if maintained, might be a useful approach for preventing and treating type 2 diabetes, though more research is needed,” said lead investigator Kirsten Dorans, ScD, assistant professor of epidemiology at Tulane University School of Public Health and Tropical Medicine, in a statement.

The growing burden of diabetes on population-level has placed a renewed emphasis on the impact of lifestyle management and factors on disease course in prediabetes and diabetes. Citing a limited knowledge base related to the effects of a low-carbohydrate diet on glycemic control in people with diabetes and prediabetes, Dorans and a team of colleagues sought to estimate how adherence to such a diet might influence HbA1c among people with untreated, but elevated HbA1c.

To do so, investigators designed their trial to compare a low carbohydrate diet intervention or usual diet among a population of patients aged 40-70 years with an untreated HbA1c of 6.0-6.9%. Participants for the trial were recruited from an academic medical center in New Orleans, LA from September 2018-June 2021. Per trial protocol, those randomized to a low-carbohydrate diet intervention had a target of less than 40 net grams of carbohydrates during the first 3 months and few than 60 net grams for months 3-6.

A total of 2722 participants were identified for potential inclusion. Of these, 962 underwent screening and 150 were randomized, with 75 randomized to the low-carbohydrate dietary interventions and 75 randomized to usual diet. At baseline, the 150-person cohort had a mean HbA1c of 6.16% (SD, 0.30%), a mean age of 58.9 (SD, 7.9) years, 72% were women, and 59% were Black. At the time of analysis, 6-month data had been collected from 142 (95%) participants.

Results of the investigators’ analysis suggested adherence to a low-carbohydrate dietary intervention was associated with significantly greater reductions 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) at 6 months compared to adherence to usual diet. In analyses of exploratory outcomes, results indicated adherence to a low-carbohydrate diet was associated with significantly greater 6-month decreases in fasting insulin, HOMA-IR, and waist circumference were compared with usual diet.

“We already know that a low-carbohydrate diet is one dietary approach used among people who have Type 2 diabetes, but there is not as much evidence on effects of this diet on blood sugar in people with prediabetes,” Dorans added. “Future work could be done to see if this dietary approach may be an alternative approach for Type 2 diabetes prevention.”

This study, “Effects of a Low-Carbohydrate Dietary Intervention on Hemoglobin A1c,” was published in JAMA Network Open.