, new research suggests.
In the 12-week study of 57 people with T2D who were not using insulin, C-peptide levels were significantly higher among those randomized to receive a low-carbohydrate diet (~9% of total calories) vs a higher-carbohydrate diet (~55%). The results were published online on October 22, 2024, in The Journal of Clinical Endocrinology & Metabolism.
“While other studies have demonstrated metabolic health benefits of low-carb diets, our results are the first to show that dietary carbohydrate restriction can improve beta-cell function ... Furthermore, the carbohydrate-restricted diet improved insulin secretion in African American patients to a much greater extent than in Caucasian Americans,” study author Marian L. Yurchishin, MS, Department of Nutrition Sciences, The University of Alabama, Birmingham, Alabama, told Medscape Medical News.
Yurchishin added, “Our data suggests that a carbohydrate-restricted diet provides the opportunity to improve beta-cell function without the need for medication use or weight loss. This approach may be more appealing and effective for some persons with T2D, particularly in patients of African descent.”
At the same time, she clarified, “Our research should not be interpreted to mean that a carbohydrate-restricted diet can replace medical therapy in those who need it, especially patients at risk of cardiovascular disease, heart failure, or chronic kidney disease…or when medications are needed to achieve A1c targets.”
Asked to comment, Alison B. Evert, RDN, CDCES, former (now retired) manager of the Nutrition and Diabetes Education Programs at the University of Washington Medicine Primary Care, Kirkland, Washington, expressed some caveats about the findings, noting “I doubt this approach would be sustainable for the average person.”
Evert also pointed out that the amount of fat in the carbohydrate-restricted diet — 65% of energy vs just 20% of energy with the higher-carbohydrate diet — was “extremely high ... essentially a keto diet,” and that in the real-world people might not receive education on heart-healthy fat intake. Moreover, she noted that the study’s use of grocery delivery to the participants with instructions for food preparation “is not a real-world situation either.”
Low-Carbohydrate Diet Increased C-Peptide Levels
The study participants were all either African American or European American. All had been diagnosed with T2D within the past 10 years, with average 4.9 years in the carbohydrate-restricted group vs 3.0 years in the higher-carbohydrate group. The two diets contained approximately the same number of calories.
All their medications were discontinued 1-2 weeks prior to baseline testing.
A hyperglycemic clamp was used to assess the acute (first-phase) and maximal (arginine-stimulated) C-peptide response to glucose at baseline and after 12 weeks of following the diets. First-phase beta-cell response to glucose was assessed at 30 minutes, insulin sensitivity was evaluated at 2 hours, and maximal beta-cell response to arginine was evaluated after another 30 minutes.
Oral glucose tolerance tests were also conducted at baseline and at 12 weeks to determine the disposition index (DI), a marker of beta-cell function that factors in both C-peptide and insulin sensitivity.
Of 65 participants enrolled, eight discontinued the study, most due to non-adherence. At 12 weeks, the acute C-peptide response from baseline was twice as high with the carbohydrate-restricted diet than with the higher-carbohydrate diet (P < .05). This difference was significant among the 37 African Americans (110% greater; P < .01) but not for the 20 European Americans.
Evert said that because people have typically lost at least 50% of their beta-cell function at the time of T2D diagnosis, “it is helpful to have return of first phase response, but long-term discontinuation of medications that also have cardioprotective function seems short sighted in this patient population.”
The overall maximal C-peptide response was 22% greater with the carbohydrate-restricted diet (P < .05), this time only significant in the European Americans (48%; P < .01) but not the African Americans.
In the combined group, the DI was 32% greater with the carbohydrate-restricted diet (P < .05) but only significantly so in the African American participants (48%; P < .01); however, no DI changes were seen with the higher-carbohydrate diet in the European American participants.
Regarding the racial differences, Yurchishin explained “Research supports the contention that the pathophysiology of T2D differs can differ among races based on genetic factors and environmental interactions that affect beta-cell function. For example, T2D onset in African Americans may be less related to obesity and insulin resistance than it is in European Americans and depend on alterations in beta-cell function to a larger degree. While sociocultural factors do influence T2D risk, other studies have also shown that there are inherent biological differences in the mechanisms that lead to beta-cell failure between races that warrant further investigation.”
In their paper, Yurchishin and colleagues concluded, “With the caveat that carbohydrate restriction may be difficult for some patients, such a diet may allow patients with mild T2D to discontinue medication and enjoy eating meals and snacks that meet their energy needs while improving beta-cell function, an outcome that cannot be achieved with medication.”
Evert commented, “I think it is a bit subjective to say that people following a 9% carb intake ‘will enjoy eating their meals and snacks that meet their energy needs.’ Guess they would enjoy as long as they choose very high fat, low carb foods.”
The research was supported by the National Institute of Diabetes and Digestive and Kidney Diseases, the UAB Nutrition Obesity Research Center, and the UAB Diabetes Research Center. Yurchishin was supported by the National Heart, Lung, and Blood Institute. Evert had no disclosures.
A version of this article appeared on Medscape.com.