Patients with type 2 diabetes who follow a low carbohydrate diet (LCD) for at least 6 months appear to have significantly higher remission rates than those following other diets, although the benefits diminish by 12 months, suggests a new analysis of trial data from over 1300 individuals.
“Based on other evidence, it is likely the degree of weight loss would have been a contributing factor, combined with the lower intake of dietary carbohydrates,” study coauthor Grant D. Brinkworth, PhD, Commonwealth Scientific and Industrial Research Organisation, Sydney, Australia, told Medscape Medical News.
He acknowledged, however, that “Diets in general can be difficult to sustain over the long term…We need to provide patients with easy-to-use support tools and convenient solutions to help them adhere to a low-carb diet long term to gain these greater health improvements.”
“In addition, more long-term, well-controlled, randomized trials are needed to determine the effects of low-carb diets on sustained weight loss, diabetes remission, and health outcomes,” Brinkworth added.
The research was published on January 13 in BMJ by a consortium of international scientists, led by Joshua Z. Goldenberg, PhD, Department of Nutrition, Texas A&M University, College Station.
Confusion as to Best Diet For Those With Diabetes
Type 2 diabetes is a “significant and worsening” worldwide health problem, say Goldenberg and coauthors, in spite of “many pharmaceutical developments and a global emphasis on glycemic control.”
Although structured diets are “recognized as an essential component of treating diabetes, confusion remains about which diet to choose,” with multiple systemic reviews and meta-analyses of carbohydrate-restricted diets “reporting mixed results,” they note.
They therefore undertook a systematic review of randomized controlled trials on the efficacy and safety of LCDs and very low carbohydrate diets (VLCDs) using the CENTRAL, Medline, CINAHL, and CAB databases, as well as other literature sources.
Researchers defined LCDs as < 130 g/day of carbohydrates or < 26% of calories from carbohydrates as part of a 2000 kcal/day diet and VLCDs as < 50 g/day or < 10% of daily calories. They focused on interventions that lasted at least 12 weeks in adults with type 2 diabetes.
Overall, 23 trials involving 1357 participants met the inclusion criteria; 52% used VLCDs and the control comparator was a low-fat diet in 78% of the studies. The mean age range of patients was 47-67 years, and treatment duration spanned from 3 months to 2 years.
LCDs were associated with a higher rate of diabetes remission when defined as an A1c < 6.5% compared with control diets at 6 months, at 57% versus 31% — an increase in remission of 32% associated with LCDs (P < .001 for overall effect).
But when defined more tightly as an A1c < 6.5% in the absence of diabetes medications, remission with LCDs was reduced to a nonsignificant 5% versus control diets at 6 months.
At 12 months, data on remission were sparse, ranging from a small effect to a trivial increased risk of diabetes.
Subgroup analysis demonstrated that patients on an LCD achieved greater weight loss at 6 months than those on a control diet, at a mean reduction of 3.46 kg (approximately 7.6 lb). However, the researchers note that, at 12 months, any weight loss benefit was “trivial and nonsignificant.”
A similar pattern was seen for reductions in A1c and fasting glucose levels with LCDs: notable reductions at 6 months largely disappeared by 12 months.
LCDs were also associated with “greater reductions in diabetes medication and clinically important benefits” in triglycerides and insulin resistance at 6 and 12 months, the team says.
VLCDs: Adherence Is Key
Finally, the team looked at weight loss achieved with VLCDs.
VLCDs were less effective for weight loss at 6 months than less restrictive LCDs. However, this effect was explained by diet adherence, the researchers note.
Restricting the analysis to “credible” studies, VLCDs were associated with a larger “clinically important” weight loss versus control diets when patients were highly adherent to the diet, at a mean reduction of 4.47 kg (9.9 lb) versus a mean increase of 0.55 kg (1.2 lb) among patients who were less adherent.
The team note that their review has a number of limitations, not least of which is the definition of diabetes remission used, which “is the subject of considerable debate,” as well as the safety concerns raised over LCDs.
Given the latter concerns, “Clinicians might consider short-term LCDs for management of type 2 diabetes, while actively monitoring and adjusting diabetes medication as needed,” they conclude.
This study was funded in part by Texas A&M University. Johnston has reported receiving funding from Texas A&M AgriLife Research for a separate research project. Brinkworth is author of the book “The CSIRO Low Carb Diet,” but does not receive financial royalties or funds either directly or indirectly.
BMJ 2021;372:m4743. Full text
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