Low-Carbohydrate Diet Contributed to Better Glycemic Control in Patients With Diabetes

A study published in Annals of Internal Medicine found improved glycemic control and weight in participants with type 2 diabetes assocated with a low-carbohydrate, high-fat (LCHF) diet compared with a high-carbohydrate, low-fat (HCLF) diet. However, these changes were not sustainable post intervention.

Type 2 diabetes affects approximately 480 million people across the globe. Weight loss has been found to improve glycemic control as well as nonalcoholic fatty liver disease (NAFLD). Reduction in energy intake is a proven way to lose weight to help in these areas. This study aimed to demonstrate the effects of a calorie-unrestricted LCHF diet compared with an HCLF diet over 6 months.

The prospective, parallel-group randomized controlled trial was done over a 6-month period and took place in Denmark. Participants were assigned to an LCHF diet or an HCLF diet randomly. Assessments were done at baseline, 3 months, 6 months, and 9 months, with the latter 2 points corresponding to the end of the intervention and postintervention periods, respectively. Participants were recruited from November 29, 2016, until June 30, 2020.

Participants were eligible for inclusion if they were 18 years or older, spoke Danish, were diagnosed with type 2 diabetes, had a hemoglobin A_1c (HbA_1c) above 48 mmol/mol, had stable diabetes treatment for 3 months before inclusion, and had a serum total cholesterol level below 4.5 mmol/L and low-density lipoprotein (LDL) cholesterol level below 2.5 mmol/L. Patients were excluded if they had excessive weight loss within the previous 3 months, a history of excessive alcohol use, or important comorbidities.

The LCHF diet consisted of intakes of a maximum of 20 energy percent (E%) carbohydrates, 50E% to 60E% fats, and 25E% to 30E% proteins; the HCLF diet consisted of 50E% to 60E% carbohydrates, 20E% to 30E% fats, and 20E% to 25E% proteins. Insulin doses were also lowered by 20% at baseline to avoid hypoglycemia.

There were 165 participants included in this study; 134 completed the trial with the LCHF diet, and 42 completed the HCLF diet. There were 123 patients who participated in the postintervention visit. The participants had a mean (SD) age of 56 (10) years, and 58% were women. The LCHF group had a lower HbA_1c compared with the HCLF group at baseline. There were 141 participants who had NAFLD.

Both groups had similar total energy intakes at baseline. Participants in the LCHF group reduced their self-reported calorie intake by 98 kcal/d and the HCLF group reduced it by 211 kcal/d during the intervention. Level of physical activity remained the same within the groups. Participants reduced their antidiabetic medications during the intervention more so in the LCHF group compared with the HCLF group.

Both groups had improved HbA_1c at 3 and 6 months, although it improved more in the LCHF group with a mean difference in change of –6.1 mmol/mol (95% CI, –9.2 to –3.0 mmol/mol) after 6 months, equal to a reduction of –0.59% (95% CI, –0.87% to –0.30%).

LDL cholesterol and apolipoprotein B increased in the LCHF group whereas it decreased in the HCLF group. Triglycerides were reduced and high-density lipoprotein cholesterol was increased in both groups, with the LCHF group seeing the largest improvements. The LCHF group had improvements in metabolic markers such as weight, waist circumference, and insulin resistance at 6 months, but these improvements were not sustained post intervention.

Also, 16 participants in the LCHF group and 6 in the HCLF group had 2 or more improvements in NAFLD Activity Score. More participants in the LCHF group had a point of improvement in NAFLD Activity Score compared with the HCLF group, with fewer participants worsening in the LCHF group compared with the HCLF group. More participants in the LCHF group reported adverse events compared with the HCLF group.

There were some limitations to this study. The design was open-label and all participants reduced calorie intake despite the isocaloric design. The improvements may have been due to weight loss achieved in the period. Multiple comparisons were not adjusted for, which gives a risk of false discovery. The reduction of insulin was only done for the LCHF group. Diet adherence assessment was self-reported.

The researchers concluded that a 6-month, calorie-unrestricted LCHF diet was better at improving glycemic control and weight in people with type 2 diabetes compared with a HCLF diet.

Reference

Hansen CD, Gram-Kampmann EM, Hansen JK, et al. Effect of calorie-unrestricted low-carbohydrate, high-fat diet versus high-carbohydrate, low-fat diet on type 2 diabetes and nonalcoholic fatty liver disease: a randomized controlled trial. Ann Intern Med. Published online December 13, 2022. doi:10.7326/M22-1787