Evidence of Low Carb Diets for Diabetes Management

Type 2 diabetes mellitus (T2DM) is a common, long-term health issue related to how your body processes sugar. Before being diagnosed with T2DM, many people go through a stage called prediabetes, where their blood sugar levels are higher than normal but not yet at the diabetes level. It has been found that lifestyle changes can frequently prevent and delay the development of T2DM, and they can also lead to disease remission. However, these methods are not used as much as they should be, and many primary care doctors have limited knowledge about them [1].

In recent years, a growing body of evidence suggests that the Ketogenic Diet may offer benefits for T2DM.

Low Carb Ketogenic Diet

The Low Carb Ketogenic Diet (LCKD) is a way of eating where you limit your carbohydrate intake to less than 50g or less than 10% of your total calorie intake. This helps your body enter a state called “ketosis.” However, it’s important to understand that being in ketosis doesn’t necessarily mean you’re following a ketogenic diet. To truly be on a ketogenic diet, you need to reduce carbs and add a significant amount of fat as your calorie source. But remember, you can achieve ketosis by lowering carb intake without consuming extra fat calories, i.e. in starvation state.

Diabetes Diet vs. Ketogenic Diet

In a 2014 clinical study, researchers compared the effects of two diets on diabetes patients: a medium carbohydrate, low-fat, calorie-restricted diet (MCCR) and a low-carb ketogenic diet (LCKD). After 3 months, the LCKD group showed better improvement in blood glucose levels (HbA1c) and reduced diabetes medication usage compared to the MCCR group. However, insulin resistance (HOMA-IR) did not significantly improve in either group [2,3].

Calorie Restriction vs. Ketogenic Diet

In a year-long study, 115 obese diabetes patients followed either a Low Carb Diet (LCKD) or a High Carb Diet, both reducing calorie intake by about 30%. After 52 weeks, both groups showed similar improvements in HbA1c and HOMA-IR. The LCKD group had increased HDL and reduced diabetes medication usage. The study extended to two years, showing sustained benefits in HbA1c and decreased medication usage for the LCKD group, with no micronutrient deficiencies observed [4-6].

Low GI Diet vs. Ketogenic Diet

The glycemic index (GI) measures how quickly blood sugar levels rise after eating compared to glucose. Foods with lower GI cause slower glucose release, leading to smaller blood sugar spikes and reduced insulin needs. In a 2008 study, 48 type 2 diabetes patients followed a LCKD, and 49 patients followed a low GI diet with a 500-calorie reduction. After 24 weeks, the LCKD group showed greater improvements in HbA1c, weight loss, and reduced diabetes medication usage. HOMA-IR, reflecting insulin resistance, also improved more in the LCKD group [7].

Low Carb, Non-Ketogenic Diet

In a trial with 10 obese participants, the daily calorie intake was reduced by approximately 1000 kcal for 14 days, resulting in a low-carb calorie-restricted diet that did not drop below 10% of calories. Despite the short trial period, the participants experienced significant benefits, including weight loss, normalized insulin levels within 24 hours, a drop in HbA1c, 75% improvement in insulin sensitivity, and a 35% decrease in triglycerides [8].

In a study on diabetes patients, they followed a low carb diet for six months, and their weight decreased from 100.6kg to 89.2kg, and their HbA1c decreased from 8.0% to 6.6%. However, after the study, when they were less strict with their diet, their weight went up to 93.1kg at 44 months. The HbA1c levels at 22 and 44 months were 6.9% and 6.8%, respectively. The low carb diet had positive effects on blood sugar and weight control in the long term, but it didn’t completely resolve diabetes [9].

Limitation of Low Carb Diet

While the extremely low carb ketogenic diet has strong research evidence supporting its therapeutic effects, it has limitations. Short-term use may negatively impact gut microbiota and increase inflammation [10]. Even probiotic supplementation cannot reverse the reduction in gut microbiota diversity [11]. Some studies suggest it may increase inflammatory markers like CRP [12].

Moreover, the diet’s many restrictions make long-term adherence challenging for diabetes patients. Essential healthy foods like fruits, whole grains, and legumes may be limited, and excessive saturated fat intake poses long-term health risks [13].

Considering the limitations of the Ketogenic Diet, Dr. Brouns from the University of Massachusetts proposed a middle ground for diabetes patients concerned about its safety [14]. He suggests that any calorie-reducing diet can lead to weight loss and metabolic improvements, without needing to be strictly ketogenic. Short-term studies on ketogenic diets show mixed effects, and long-term adherence can be challenging with limited evidence from long-term studies. Dr. Brouns recommends controlling carbohydrate intake between 100g-150g, which he considers more feasible and suitable.

Summary

Lifestyle changes and dietary approaches can prevent and delay T2DM, but they are underutilized, and primary care doctors have limited knowledge about them.

Recent evidence suggests the Ketogenic Diet may offer benefits for managing T2DM.

Other low carb diets have also shown effectiveness in improving blood sugar control and insulin resistance.

Considering the limitations of low carb and Ketogenic Diets, a middle-ground approach that focuses on calorie reduction and controlled carbohydrate intake may be beneficial for improving diabetes management.