Effects of a Low-Carbohydrate Dietary Intervention on Hemoglobin A1c: A Randomized Clinical Trial.
Study Goal
The researchers aimed to determine whether a low-carbohydrate dietary intervention, compared to a usual diet, could improve HbA1c levels in individuals with elevated but untreated HbA1c (prediabetes to diabetes range).
Results Summary
The low-carbohydrate diet group showed significantly greater reductions in HbA1c, fasting plasma glucose, and body weight compared to the usual diet group over 6 months. The study suggests this dietary approach may be useful for preventing and treating type 2 diabetes, though effects independent of weight loss could not be evaluated.
Population
Adults aged 40-70 years with untreated HbA1c levels of 6.0% to 6.9% (prediabetes to diabetes range).
Effective Dosage
Target <40 net grams of carbohydrates during the first 3 months; <60 net grams for months 3 to 6.
Duration
6 months
Interactions
None mentioned
| Intervention | Direction | Endpoint | Population | Dosage | Impact | Claim # |
|---|---|---|---|---|---|---|
low-carbohydrate diets | decrease | hemoglobin A1c (HbA1c) | patients with type 2 diabetes | - | decrease | #1 |
behavioral intervention promoting a low-carbohydrate diet | decrease | HbA1c | individuals with elevated untreated HbA1c | -0.23% | significantly greater 6-month reductions | #2 |
behavioral intervention promoting a low-carbohydrate diet | decrease | fasting plasma glucose | individuals with elevated untreated HbA1c | -10.3 mg/dL | significantly greater 6-month reductions | #3 |
behavioral intervention promoting a low-carbohydrate diet | decrease | body weight | individuals with elevated untreated HbA1c | -5.9 kg | significantly greater 6-month reductions | #4 |
low-carbohydrate dietary intervention | decrease | glycemia | individuals with elevated HbA1c not taking glucose-lowering medication | - | led to improvements | #5 |
IMPORTANCE: Low-carbohydrate diets decrease hemoglobin A1c (HbA1c) among patients with type 2 diabetes at least as much as low-fat diets. However, evidence on the effects of low-carbohydrate diets on HbA1c among individuals with HbA1c in the range of prediabetes to diabetes not treated by diabetes medications is limited. OBJECTIVE: To study the effect of a behavioral intervention promoting a low-carbohydrate diet compared with usual diet on 6-month changes in HbA1c among individuals with elevated untreated HbA1c. DESIGN, SETTING, AND PARTICIPANTS: This 6-month randomized clinical trial with 2 parallel groups was conducted from September 2018 to June 2021 at an academic medical center in New Orleans, Louisiana. Laboratory analysts were blinded to assignment. Participants were aged 40 to 70 years with untreated HbA1c of 6.0% to 6.9% (42-52 mmol/mol). Data analysis was performed from November 2021 to September 2022. INTERVENTIONS: Participants were randomized to a low-carbohydrate diet intervention (target <40 net grams of carbohydrates during the first 3 months; <60 net grams for months 3 to 6) or usual diet. The low-carbohydrate diet group received dietary counseling. MAIN OUTCOMES AND MEASURES: Six-month change in HbA1c was the primary outcome. Outcomes were measured at 0, 3, and 6 months. RESULTS: Of 2722 prescreened participants, 962 underwent screening, and 150 were enrolled (mean [SD] age, 58.9 [7.9] years; 108 women [72%]; 88 Black participants [59%]) and randomized to either the low-carbohydrate diet intervention (75 participants) or usual diet (75 participants) group. Six-month data were collected on 142 participants (95%). Mean (SD) HbA1c was 6.16% (0.30%) at baseline. Compared with the usual diet group, the low-carbohydrate diet intervention group had significantly greater 6-month 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). CONCLUSIONS AND RELEVANCE: In this randomized clinical trial, a low-carbohydrate dietary intervention led to improvements in glycemia in individuals with elevated HbA1c not taking glucose-lowering medication, but the study was unable to evaluate its effects independently of weight loss. This diet, if sustained, might be a useful dietary approach for preventing and treating type 2 diabetes, but more research is needed. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT03675360.