Does a ketogenic (keto) diet reduce fasting blood glucose levels?

From the Guidelines

A ketogenic diet may have a beneficial effect on fasting blood glucose levels, although the evidence is very uncertain due to serious risk of bias and imprecision in the studies 1. The keto diet works by drastically reducing carbohydrate intake and replacing it with fat, which puts the body into a metabolic state called ketosis. In this state, the body becomes more efficient at burning fat for energy and turns fat into ketones in the liver, which supply energy to the brain. When you consume fewer carbohydrates, your body produces less insulin, the hormone responsible for processing blood sugar. This reduction in insulin levels helps prevent blood glucose spikes and can lead to lower fasting glucose readings over time. Some key points to consider when evaluating the effect of a ketogenic diet on fasting blood glucose levels include:

• The definition of remission, which is either HbA1c < 48 mmol/mol (<6.5%) or fasting plasma glucose <7 mmol/l and no glucose-lowering medication 1.
• The potential benefits of weight loss, as every 1 kg of weight loss is associated with a 7% higher chance of remission at 5 years, regardless of specific diet regimens or lifestyle interventions 1.
• The importance of gradual transition to a keto diet and consultation with a healthcare provider, especially for those with existing health conditions, as the initial adaptation phase can cause fluid and mineral losses and may require adjustments to diabetes medications. It's also important to note that the evidence for the effect of a ketogenic diet on type 2 diabetes remission is very uncertain, with a GRADE level of 'very low' due to serious risk of bias and imprecision in the studies 1.

From the Research

Effects of a Ketogenic Diet on Fasting Blood Glucose Levels

• The ketogenic diet has been shown to improve glycemic control in patients with type 2 diabetes, with studies indicating a reduction in fasting blood glucose levels 2, 3, 4.
• A study published in 2005 found that a low-carbohydrate, ketogenic diet improved glycemic control in patients with type 2 diabetes, with a decrease in hemoglobin A1c levels from 7.5% to 6.3% over a 16-week period 2.
• Another study published in 2008 compared the effects of a low-carbohydrate, ketogenic diet to a low-glycemic index diet on glycemic control in patients with type 2 diabetes, and found that the ketogenic diet led to greater improvements in hemoglobin A1c and fasting glucose levels 4.
• A review of the literature on the effects of different diets on glycemic control in patients with type 2 diabetes found that a low-carbohydrate diet had the greatest effect on improving glycemic control and insulin parameters 5.

Mechanisms of Action

• The ketogenic diet works by reducing the glycemic response to dietary carbohydrate and improving insulin resistance, which is a major underlying cause of type 2 diabetes 3.
• By reducing carbohydrate intake to a level that induces ketogenesis, the body is able to switch from relying on glucose for fuel to relying on ketones, which can improve blood sugar control and reduce the need for diabetes medications 2, 3.

Clinical Implications

• The use of a ketogenic diet in patients with type 2 diabetes may require close medical supervision, as it can lead to a reduction in the need for diabetes medications 2, 4.
• Further studies are needed to establish guidelines for the use of a ketogenic diet in patients with type 2 diabetes, including the optimal level of carbohydrate restriction and the potential benefits and risks of this dietary approach 6, 5.