Low-Carbohydrate and Ketogenic Dietary Patterns for Type 2 Diabetes Management
Background: Type 2 diabetes mellitus (T2DM) has been traditionally considered a chronic, progressive disease. Since 2017, guidelines from the US Department of Veterans Affairs and US Department of Defense have included low-carbohydrate (LC) dietary patterns in managing T2DM. Recently, carbohydrate reduction, including ketogenic diets, has gained renewed interest in the management and remission of T2DM.
Observations: This narrative review examines the evidence behind carbohydrate reduction in T2DM and a practical guide for clinicians starting patients on therapeutic LC diets. We present an illustrative case and provide practical approaches to prescribing a very LC ketogenic (< 50 g), LC (50-100 g), or a moderate LC (101-150 g) dietary plan and discuss adverse effects and management of LC diets. We provide a medication management and deprescription approach and discuss strategies to consider in conjunction with LC diets. As patients adopt LC diets, glycemia improves, and medications are deprescribed, hemoglobin A1c levels and fasting glucose may drop below the diagnostic threshold for T2DM. Remission of T2DM may occur with LC diets (hemoglobin A1c < 6.5% for ≥ 3 months without T2DM medications). Finally, we describe barriers and limitations to applying therapeutic carbohydrate reduction in a federal health care system.
Conclusions: The effective use of LC diets with close and intensive lifestyle counseling and a safe approach to medication management and deprescribing can improve glycemic control, reduce the overall need for insulin and medication and provide sustained weight loss. The efficacy and continuation of therapeutic carbohydrate reduction for patients with T2DM appears promising. Further research on LC diets, emerging strategies, and long-term effects on cardiometabolic risk factors, morbidity, and mortality will continue to inform practice.
Low-Carbohydrate T2DM DIET MANAGEMENT
LC diets are commonly defined as < 130 g of carbohydrates per day.13 Very LC ketogenic (VLCK) diets often contain ≤ 50 g of carbohydrates per day to induce nutritional ketosis.13 One of the first randomized controlled trials (RCTs) that compared a VLCK diet (< 30 g of carbohydrates per day) with a low-fat diet for obesity demonstrated greater weight loss at 6 months with the LC diet. In addition, patients with diabetes randomized to the LC group also showed improved insulin sensitivity. Notably, this study was done in a population of veterans enrolled at the VA Philadelphia Health Care System.14
A 2008 study comparing an LC diet with a calorie-restricted, low-glycemic diet for individuals with T2DM found that the LC diet group experienced a greater reduction in HbA1c and insulin levels and weight.15 Comparing these 2 diet groups after 24 weeks, 95% of individuals in the LC group reduced or discontinued T2DM medications vs 62% in the low-glycemic group.15 Another study of individuals with T2DM compared a VLCK diet with a low-fat diet. After 34 weeks, 55% of individuals in the LC diet group achieved an HbA1c level below the threshold for diabetes vs 0% in the low-fat diet group.16 A 2018 study of patients with T2DM investigated the impact of a very LC diet compared with the standard of care.17 After 1 year, the LC diet group experienced a mean HbA1c reduction of 1.3%, and 60% of individuals who completed the study achieved an HbA1c level < 6.5% without T2DM medications (not including metformin). This study also demonstrated that medications were significantly reduced, including 100% discontinuation of sulfonylureas and 94% reduction or elimination of insulin.
A recent study of an LC diet (< 20% energy from carbohydrates) demonstrated reduced HbA1c levels, weight, and waist circumference vs a control diet after 6 months. The control diet derived 50% to 60% of energy from carbohydrates.18 This study is typical of other LC interventions, which did not calorie restrict and instead allowed ad libitum intake.14,15
With mounting evidence, the VA/DoD guidelines on T2DM management included LC diets as dietary options for treating T2DM. The ADA also determined that LC diets had the most evidence in improving glycemia and included LC diets as an option for medical nutrition therapy (Table 1).10,19
A systematic review and meta-analysis looking at RCTs of LC diets found evidence for remission of T2DM without significant adverse effects (AEs).20 Another recent systematic review and network meta-analysis of 42 RCTs found that the ketogenic diet was superior for a reduction in HbA1c levels compared with 9 other dietary patterns, including low-fat, Mediterranean, and vegetarian/vegan diets. Overall, ketogenic, Mediterranean, moderate-carbohydrate, and low-glycemic index diets demonstrated improved glycemic control.21
Ideally, a comprehensive behavioral program, such as the VA Move! or Whole Health program, should incorporate patient aligned care teams (PACTs), behavioral health clinicians, clinical pharmacists, and dietitians to provide medical-nutrition therapy using LC diets. However, many facilities may not have adequate experience, expertise, or support. We provide practical approaches to provide LC nutrition counseling, medication management, and deprescribing for any primary care clinician applying LC diets for their patients. For simplicity and practicality, we define 3 types of LC dietary patterns: (1) VLCK (< 50 g); (2) LC (50-100 g); and (3) moderate LC (101-150 g).
Nutrition
All nutrition approaches, including LC diets, should be patient centered, individualized, and sensitive to the patient's culture. Typically, many patients have previously been instructed to consume low-fat (and subsequently) high-carbohydrate (> 150 g) meals. Most well-meaning clinicians have provided common-approach diet education from mainstream health organizations in the form of standardized handouts. For example, the Carbohydrate Counting for People with Diabetes patient education handout from the Academy of Nutrition and Dietetics provides a sample menu with 3 meals and 1 snack totaling 195 g of carbohydrates.22 In contrast, an example ADA diet has sample diets with 3 meals and 2 snacks with approximately 20 to 70 g of carbohydrates.23 In the VA, there are excellent resources to review and standardize handouts that emphasize an LC nutrition approach to T2DM, including ketogenic versions.24,25 Table 2 shows example meal plans based on different LC patterns—VLCK, LC, and moderate LC.
