Comparing the effects of a ketogenic diet versus a Mediterranean diet on glucose control in patients with prediabetes and type 2 diabetes.

This study compared the effects of a ketogenic diet (KD) versus a Mediterranean diet (MD) on glucose control in patients with prediabetes and type 2 diabetes (T2D). The data showed that the less restrictive MD was as effective in controlling glucose as a KD and likely more likely to be maintained in the long term. There were no additional overall health benefits to cutting out legumes, fruits, and whole grains to achieve an ultra-low-carbohydrate KD in these patients.

Patients with prediabetes are at a high risk of developing T2D. T2D is a condition in which patients have high blood sugar (glucose) levels (hyperglycemia). Long-term high blood glucose levels can damage blood vessels, nerves, and organs. This can lead to complications such as heart attack, high blood pressure, stroke, kidney disease, loss of sight, and nerve damage. Diet plays an important role in the management of T2D. A healthy diet can help in controlling blood glucose levels, managing weight, and reducing complications.

A KD is based on changing the way the body uses energy. Normally, the body primarily uses blood glucose as a source of energy. The body gets glucose from carbohydrates. A KD strictly limits carbohydrates in the diet, such as bread, root vegetables, or beans. When the body does not have access to glucose, it can break down fat into ketones (acids made by the liver) to use as fuel. A KD may improve glucose control. Because this diet includes fat and protein, it can prevent hunger even when calories are reduced. An effective KD causes the patient to have an acetone breath (a fruity scent like nail polish).

The MD and low-fat diets are effective in the primary prevention of cardiovascular disease. The MD includes a high intake of fruits, vegetables, legumes, cereals, white meat, fish, and olive oil. It is important to evaluate the effects of these two diets on glucose control in patients with prediabetes and T2D.

The study involved 40 patients with prediabetes or T2D. 20 patients were on a well-formulated KD and 20 patients followed the MD over a period of 12 weeks. After 12 weeks, the patients swapped diets for an additional 12 weeks. This crossover allowed participants to act as their own controls.

After 12 weeks, the glycosylated hemoglobin (average blood glucose over the last 3 months; HbA1c) levels were reduced by 9% in patients on a KD and by 7% in patients on an MD. This difference was not statistically significant.

After 12 weeks, triglycerides (a type of fat found in the blood) levels were reduced by 16% in patients on a KD and by 5% in patients on a MD. This difference was statistically significant.

LDL cholesterol (the "bad" cholesterol) levels increased by 10% in patients on a KD diet and reduced by 5% in patients on the MD. This difference was statistically significant. HDL cholesterol (the "good" cholesterol) levels increased by 11% in patients on a KD and increased by 7% in patients on a MD.

After 12 weeks, weight decreased similarly by 8% in patients on a KD and by 7% in patients on a MD. 

Patients had lower intakes of fiber and 3 nutrients (legumes, fruits, and whole grains) on a KD compared with the MD. Overall, the MD was considered more sustainable over the long-term. 

This study concluded that for people with prediabetes or T2D, the less restrictive Mediterranean diet was as effective in controlling blood glucose as a KD and likely more sustainable in the long term. There were no additional overall health benefits to cutting out legumes, fruits, and whole grains to achieve an ultra-low-carbohydrate KD in these patients.

The sample size was very small. This study did not measure the blood pressure of the patients. Larger studies are necessary to validate the conclusions.