Low-carb diet may improve beta-cell function in type 2 diabetes patients

Following a low-carb diet may potentially help patients manage disease more effectively and reduce medication use.

In a recent study published in The Journal of Clinical Endocrinology & Metabolism, a group of researchers evaluated the impact of a eucaloric carbohydrate-restricted (CR) diet on beta (β)-cell (pancreatic cell that produces insulin) response to glucose in adults with type 2 diabetes (T2D) (chronic high blood sugar due to insulin resistance) compared to a higher carbohydrate (HC) diet.

Background 

β-Cell failure and insulin resistance contribute to the onset and progression of T2D, with a decline in first-phase insulin secretion playing a critical role in glucose management. Inadequate first-phase response leads to elevated glucose and insulin levels, causing complications like glycosylation (attachment of sugar to proteins or lipids) and lipid abnormalities. Existing T2D medications do not enhance first-phase secretion, and treatment costs are high.

Although bariatric surgery (surgery for weight loss by altering the digestive system) and very-low-calorie diets can improve glycemic control and β-cell function, there is a need for less invasive, sustainable solutions. Further research is essential to identify dietary interventions that restore β-cell function and to investigate racial differences in responsiveness.

About the study 

Participants in the present study included African American (AA) and European American (EA) adults with T2D, identified through self-reported race. Inclusion criteria comprised a T2D diagnosis within the past decade, treatment with dietary changes or specific medications, and being aged 35 to 65 years, with a glycated hemoglobin A1c (HbA1c) of 8.0 or lower and a body mass index (BMI) between 25 and 50. Participants with glucocorticoid use, significant weight changes, or substance abuse were excluded. Medications were paused prior to baseline assessments, and fasting glucose levels were monitored. 

Diets (CR, HC) were crafted by a registered dietitian and tailored weekly, with participants preparing their meals at a caloric level intended to maintain weight. At baseline and after 12 weeks, participants underwent a 75-g oral glucose tolerance test (OGTT) and a hyperglycemic clamp. Blood samples were collected to analyze glucose, insulin, and C-peptide levels. The first-phase C-peptide index and the Disposition Index (DI) were calculated to assess β-cell function. Statistical analyses included Analysis of covariance (ANCOVA) and paired t-tests to analyze dietary impacts on outcomes across different racial groups.

Study results 

A total of 65 participants were enrolled in the study, which included AA and EA adults diagnosed with T2D. Eight participants withdrew themselves from the study for various reasons like personal issues, nonadherence to the diet, and a coronavirus disease 2019 (COVID-19) shutdown. Ultimately, 57 participants completed the 12-week diet intervention, successfully finishing both the baseline OGTT and hyperglycemic clamp, while some participants contributed data from only one of the tests. At the outset, all participants had their medications removed. Three individuals resumed metformin during the intervention, with two assigned to the HC diet and one to the CR diet.

The ANCOVA revealed significant findings at 12 weeks regarding acute and maximal C-peptide responses. Overall, the CR diet produced a two-fold increase in acute C-peptide response compared to the HC diet, with similar significant improvements observed in the AA group, but not in the EA group. For maximal C-peptide response, the CR diet led to a 22% increase in all participants combined and a 48% increase specifically in EAs. In terms of the DI, the CR diet resulted in a 32% increase overall and a notable 48% increase in AAs.

While no changes in insulin sensitivity were detected from the hyperglycemic clamp, the Matsuda index derived from the OGTT also remained unchanged. Notably, β-hydroxybutyrate (BHB) levels were comparatively higher on the CR diet compared to the HC diet at 12 weeks, and the increase in BHB was greater in the CR group. 

Conclusions 

To summarize, results indicated that a CR diet significantly enhanced acute and maximal C-peptide responses compared to an HC diet. While insulin sensitivity remained unchanged, the CR diet showed potential as a practical approach to restore β-cell function, particularly in EA. These findings align with previous research supporting dietary carbohydrate restriction for improving metabolic health in T2D patients, suggesting that a eucaloric CR diet may enable individuals to maintain an enjoyable diet while enhancing β-cell function.