Introduction to the Glucose-Ketone Index Guide

Knowing your Glucose-Ketone Index (GKI) and how to properly calculate it is an important step to being successful with the Ketogenic Diet. Our Glucose-Ketone Guide explains the basics of measuring your GKI and understanding the results as well as how to make the needed dietary changes to improve your GKI numbers.

What is the Glucose-Ketone Index (GKI)?

The Glucose-Ketone Index (or GKI for short) is the ratio of your blood glucose levels and your blood ketone levels (both measured in mmol/dl) and gives a more accurate and standardized insight into how your body is adapting to the ketogenic diet. The initial goal of many people on the ketogenic diet is to get their body into “ketosis” with high blood ketone levels, However, the long-term benefits of the ketogenic diet are not from the elevated blood ketone levels, but from lower blood glucose levels and improved insulin sensitivity. In fact, we see a good number of people starting out on the keto lifestyle that continue to have high blood glucose levels despite having high blood ketone levels.

The Glucose-Ketone Index was first used by cancer researchers at Boston College (Joshua Meidenbauer and Thomas Seyfried) and published in the journal Nutrition & Metabolism in 2015. Their original research used the GKI to track how brain cancer patients responded to a ketogenic diet and gave the researchers a way to track both blood glucose and ketone levels and their relationship to either other.

Why should I track my Glucose-Ketone Index?

Tracking your Glucose-Ketone Index (GKI) can give you a better sense of how your body is responding to a low-carb ketogenic diet since it compares glucose AND ketone levels taken at the same time. The GKI adjusts for higher glucose levels and will help you determine if certain foods or activities are spiking your glucose levels and limiting the benefits of the ketogenic diet

How to calculate your Glucose-Ketone Index

The Glucose-Ketone Index calculation is a ratio of glucose (in mmol/dl) divided by blood ketone levels (also in mmol/dl).

glucose-ketone index (GKI) formula

How to convert your blood glucose results for the GKI

In the U.S., most glucose machines will give blood glucose results in mg/dl, so these results need to be converted to mmol/dl by dividing the mg/dl blood glucose result by 18.02.

glucose-ketone index calculation example
Converting your blood glucose results from mg/dl to mmol/dl for GKI

When to test for Glucose-Ketone Index

One common question we get is what time of day should someone test their blood glucose and blood ketones to calculate their GKI. There is no one right answer for when to test glucose and ketones, but we do recommend 1) being consistent on the time of day that you test and 2) test either fasted (after waking up in the morning, or at least 2 hours after a meal to get a more accurate blood glucose level. If you test immediately after a meal, you will most likely have a temporarily higher blood glucose level from the meal and your GKI level will be higher than it probably is throughout other times of the day.

Glucose-Ketone Index (GKI) ranges

Glucose-Ketone Index levels can be broken down into several ranges and your health and lifestyle goals typically determine in what GKI range you should be.

GKI greater than 9 – No ketosis

Most people on a normal high-carbohydrate diet are going to have a high GKI number (greater that 9). Even with a normal glucose range, high-carb dieters will have low or no measurable blood ketone levels.

GKI between 6 and 9 – Mild ketosis

Mild ketosis, with a GKI between 6 and 9 is where most of us using the ketogenic diet for weight loss will find ourselves, especially in the first months of being on the ketogenic diet as the body adapts to the higher fat, lower carb diet.

GKI between 3 and 6 – Moderate ketosis

Moderate ketosis is typically with a GKI between 3 and 6 and at this level of ketosis, Type II diabetics will usually find they have better blood glucose control and that they also have an improvement of their insulin-sensitivity. In this range, I’ve seen patients be able to decrease or even come off their insulin injections and/or decrease their oral diabetic medications as their body improves its insulin sensitivity.

GKI between 1 and 3 – Deep ketosis

A Glucose-Ketone Index between 1 and 3 is a state of deep ketosis with blood glucose levels typically in the 50-60 mg/dl (2.8 to 3.3 mmol/dl) range and blood ketone levels in the 2.0 to 3.0 mmol/dl range. This level of a Glucose-Ketone Index may be helpful for people with neurological conditions just as Parkinson’s and drug-resistance epilepsy.

GKI lower than 1 – Very deep ketosis

Most of us on a ketogenic diet won’t see our GKI under 1.0 unless we are doing extended fasting longer than 24 hours or taking exogenous ketones as well. Fortunately, most people don’t need to have their GKI lower than 1 unless they are using a ketogenic low carb diet or fasting as an adjunct treatment for cancer or for a seizure disorder.

Glucose-Ketone Index for cancer treatments

Meidenbauer and Seyfried found that a lower GKI level (below 1.0) demonstrated better efficacy of the ketogenic diet in brain cancer patients. The benefit of a ketogenic diet or fasting diet for brain cancer patients is thought to be due to the Warburg effect, where cancer cells are thought to have higher glucose energy requirements than normal cells. The cancer cells often have abnormal or dysfunctional mitochondria, which prevent the mitochondria from using fats (fatty acids) as fuel. Thus, the cancer cells require glucose to function. Dietary treatments for several types of cancers focuses on a very low-carbohydrate diet that significantly lowers blood glucose levels and increases ketone and fatty acid metabolism by the body. This lowering of carbohydrates and blood glucose limits the growth of these cancer cells in some small research studies.

How to improve your Glucose-Ketone Index

If you’re finding that your GKI number is trending higher or isn’t dropping into at least the mild ketosis range, then it’s important to go back and look at what foods you’re eating and if there are other factors affecting either your glucose or ketone levels. Some common mistakes we see is that some people are more sensitive to sugar alcohols than others and these sugar alcohols can either spike their blood glucose levels or knock them out of ketosis. Exercise, especially endurance exercises such as running can lower blood ketone levels as the body is depending on the blood ketones as a fuel source during exercise. Increase caffeine intake can also spike blood glucose levels in some people, so testing 2 to 3 hours after that cup of coffee in the morning may give you a more accurate GKI measurement.

Looking to learn more about the ketogenic diet?

Check out our Ketogenic Diet Guide with step-by-step tips on how to start your keto diet and avoid the common keto diet mistakes that others make.