Why are carbohydrates a problem in type 2 diabetes?
Our blood sugar and insulin respond very differently to different macronutrients. Fat has minimal impact, protein has moderate, and carbohydrates have a very high impact on postprandial serum glucose and insulin. Clinicians have been taking advantage of this understanding for over a century, recommending low-carbohydrate diets for managing diabetes well before insulin or medications were available. Source¹ Type 2 diabetes is a disorder of dysregulated glucose metabolism and homeostasis. Source² If an individual with pre-diabetes or type 2 diabetes eats large amounts of carbohydrates, it can cause their blood sugar to rise above a healthy level – which results in both microvascular complications (diabetic nephropathy, neuropathy, and retinopathy) and macrovascular complications (e.g. coronary artery disease, peripheral arterial disease, and stroke). Source³ Since the discovery of insulin in 1921, people who suffer from a progressive loss of adequate β-cell insulin secretion on the background of insulin resistance have been advised to inject themselves with insulin and titrate according to the amounts of carbohydrates consumed. This strong and direct relationship between dietary carbohydrates and postprandial serum glucose led to the development of medications that lower blood glucose levels and improve insulin sensitivity. This downstream, medication-based approach to type 2 diabetes means that individuals will likely be forced to take medication for the rest of their lives (and suffer the costs and side effects). We need to look upstream and address the root causes of diabetes, starting with diet.
What is the evidence supporting low carb in managing type 2 diabetes?
Source⁴ A 2018 meta-analysis of 33 randomised-controlled trials (RCTs) and three controlled clinical trials compared a low-carbohydrate diet (defined as ≤40% of calories from carbohydrate) to a low-fat eating pattern (defined as ≤30% of calories from fat) in individuals with type 2 diabetes. In trials up to 6 months long, the low-carbohydrate diet improved HbA1c more than low fat, and in trials of varying lengths, lowered triglycerides, raised HDL-C, lowered blood pressure, and resulted in greater reductions in reliance on diabetes medication. Source⁵ A 2018 Australian systematic review and meta-analysis of 25 RCTs compared the effects of low-carbohydrate diets (≤45% of total energy) to high-carbohydrate diets (>45% of total energy) on glycaemic control in individuals with type 2 diabetes. Carbohydrate-restricted diets, particularly those that restricted carbohydrates to <26% of total energy, produced a significantly greater short-term (3–6 months) reduction in HbA1c – an effect likely driven by increased weight loss. The authors conclude that low-carbohydrate diets may be at least as effective as high carbohydrate diets for long-term glycaemic control, despite no significant difference in HbA1c change and weight loss between diets at 12 and 24 months, with greater improvements in HDL-cholesterol and triglycerides. Source⁶ In a 2019 study, eleven middle-aged women (BMI 36.3 kg/m2) who were recently diagnosed with type 2 diabetes based on HbA1c over 6.5% (average 8.9%) volunteered to participate in an intensive dietary intervention to limit dietary carbohydrates to under 30 grams daily for 90 days. All eleven women lost significant weight (85 7 ± 3 2 kg to 76 7 ± 2 8 kg) and lowered systolic (134 0 ± 1 6 to 123 3 ± 1 1mmHg) and diastolic (89 9 ± 1 3 to 82 6 ± 1 0mmHg) blood pressure. Within 90 days of a low-carb diet, HbA1c dropped to 5.6%. Most blood lipids were significantly altered, including HDL cholesterol (43 1 ± 4 4 to 52 3 ± 3 3 mg/dl), triglycerides (177 0 ± 19 8 to 92 1 ± 8 7 mg/dl), and the TG:HDL ratio (4 7 ± 0 8 to 1 9 ± 0 2). LDL cholesterol was not significantly different. AST and ALT, plasma markers of liver health, were reported for eight patients and revealed no significant changes. These findings indicate that a short-term intervention emphasizing protein and fat at the expense of dietary carbohydrates functionally reversed the diabetes diagnosis, as defined by HbA1c. The low-carbohydrate diet lowered body weight and blood pressure, eliciting favourable changes in blood lipids. Source⁷ A recent community-based cohort study investigated the effects of low carbohydrate high fat diet compared with usual care in a cohort of 49 adults with type 2 diabetes. A low carbohydrate high fat diet followed for ≥3 months was associated with greater HbA1c reduction, weight loss and significantly more patients discontinuing or reducing antihyperglycemic therapies. All patients following the LCHF diet who initially took insulin had either a reduction or discontinuation of insulin therapy by their healthcare provider when clinically indicated, compared with less than a quarter of those receiving usual care. Source⁸ In another 2020 study, 35 overweight individuals with type 2 diabetes on insulin commenced a low-carbohydrate diet and were evaluated for 6 months. All individuals were advised to consume 30 grams of carbohydrates per day. They received dietary advice in the form of a daily menu. Insulin use was reduced significantly from 62.6±46.4 IU to 1.4±6.4 IU per day. For 92% of the participants, insulin injections could be stopped completely by lowering carbohydrate intake to <40 grams daily. On average, this was achieved within only a few weeks. Individuals lost a mean of 13.3±6.3 kg, and the mean HbA1c level declined from 63.4±11.0mmol/mol to 56.9±13.0mmol/mol.
Can diabetes programs be delivered online?
In recent years, highly effective digitally delivered programs in the UK and US have transformed how diabetes care is delivered. Source⁹ A recent UK study reviewed results from the Low Carb program on diabetes.co.uk, with over 400,000 participants. Of the 743 participants in the study with a starting HbA1c at or above the type 2 diabetes threshold of 6.5%, 195 (26.2%) reduced their HbA1c to below the threshold while taking no glucose-lowering medications or just metformin. Of the participants taking at least one hypoglycemic medication at baseline, 40.4% (289/714) reduced one or more of these medications. Almost half (46.40%, 464/1000) of all participants lost at least 5% of their body weight. Overall, glycemic control and weight loss improved, especially for participants who completed all 10 modules of the program. For example, participants with elevated baseline HbA1c (≥7.5%) who engaged with all 10 weekly modules reduced their HbA1c from 9.2% to 7.1% (P<.001) and lost an average of 6.9% of their body weight (P<.001). Source¹⁰ In the USA, Virta Health’s remote care model of low-carbohydrate diets for type 2 diabetes has produced impressive results. Virta Health has published data annually, with the latest research showing results after 2 and 3.5 years. The 2-year results demonstrated the use of any glycemic control medication (excluding metformin) among participants declined (from 55.7 to 26.8%), including insulin (-62%) and sulfonylureas (-100%). There was also a resolution of diabetes (reversal, 53.5%; remission, 17.6%) in the treatment group. Source¹¹ After 3.5 years, 50.2% of diabetes medications and 71.4% of diabetes medications other than metformin were discontinued. 45.5% (65/143) of participants achieved HbA1c <6.5% with either no medication (34/65, 52%) or only metformin (31/65, 48%) at 3.5 y; 37.8% of participants maintained this status from 1 through 3.5 y of treatment. 22% of participants achieved diabetes remission at 3.5 y, and 17.5% maintained remission status from 2 through 3.5 y of treatment. This demonstrates that clinically meaningful improvements across multiple markers of metabolic risk can be sustained in patients with type 2 diabetes who selected this treatment regimen for 3.5 years.
⁴ Effects of low-carbohydrate- compared with low-fat-diet interventions on metabolic control in people with type 2 diabetes: a systematic review including GRADE assessments ⁵ Effect of dietary carbohydrate restriction on glycemic control in adults with diabetes: A systematic review and meta-analysis ⁶ Improvement in Glycemic and Lipid Profiles in Type 2 Diabetics with a 90-Day Ketogenic Diet ⁷ Effects of the low carbohydrate, high fat diet on glycemic control and body weight in patients with type 2 diabetes: experience from a community- based cohort ⁸ Low Carbohydrate Lifestyle Reduces Significantly Insulin Need in Type 2 Diabetes Patients ⁹ Outcomes of a Digitally Delivered Low-Carbohydrate Type 2 Diabetes Self-Management Program: 1-Year Results of a Single-Arm Longitudinal Study ¹⁰ Long-Term Effects of a Novel Continuous Remote Care Intervention Including Nutritional Ketosis for the Management of Type 2 Diabetes: A 2-Year Non-randomized Clinical Trial ¹¹ A Continuous Remote Care Intervention Utilizing Carbohydrate Restriction Including Nutritional Ketosis Improves Markers of Metabolic Risk and Reduces Diabetes Medication Use in Patients With Type 2 Diabetes Over 3.5 Years