Reviewing the significance of very low carbohydrate diets in type 2 diabetes.

This study compared the effect of very low carbohydrate (VLC) or ketogenic diets (KDs) with higher carbohydrate diets in patients with pre-diabetes or type 2 diabetes (T2D). The data showed that reduced levels of glycated hemoglobin (HbA1c) and triglycerides may occur with VLC or KDs, but with limited advantages over other diets.

Risk factors that predispose individuals to T2D include pre-diabetes, obesity, unhealthy diet, and reduced physical activity. Pre-diabetes occurs when a person’s blood glucose level is higher than normal but not at the level of a diabetic. A body mass index (BMI) greater than or equal to 25 kg/m² is considered overweight. A BMI that is 30 kg/m² or higher is known as obesity.

A KD consists of a very low carbohydrate intake and fat-rich foods. This type of diet uses an alternative source of fuel to glucose called ketone bodies. This dietary intervention has gained attention over the years with reported benefits of weight loss, better control of diabetes, and reduced insulin requirements. However, it remains unclear whether it provides clear advantages for HbA1c levels (blood glucose control over the past 2-3 months).

This analysis included 8 studies with 606 participants that had pre-diabetes or T2D. Studies were at least 6 months in duration and compared the effectiveness and safety of VLC or KDs with a control diet. Participants given VLC or KDs had 50 grams or less of carbohydrates per day or 10% or less total energy from carbohydrates every day. HbA1c levels and serum triglycerides (blood fats) were determined.

Reductions in HbA1c and serum triglycerides were observed in participants that received VLC/KDs compared to control diets. On average, there was a difference in HbA1c levels of 0.65% between these diets at 12 months.

This study showed that after 12 months, VLC or KDs showed modest improvements in blood glucose control and blood fats, in patients with prediabetes and T2D. However, they did not significantly improve weight loss, body composition, or blood pressure compared to alternative diets in these patients.

The study included a high number of participants that did not complete the duration of the study. The use of diabetic, cholesterol-reducing, and fat-lowering medications differed across studies. The effect of physical activity on HbA1c was not assessed. These may have affected the interpretation of results.