GKI – Glucose Ketone Index Guide (Updated)

Introduction to the Glucose Ketone Index (GKI) 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 Index 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 Glucose-Ketone Index 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 continues 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 each 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.

I also find that using the Glucose-Ketone Index instead of just blood ketone levels helps give a more accurate representation of how your body is handling the longer-term effects of the ketogenic diet. 

For some people, they will have high blood ketone levels the first few months on a ketogenic diet but then will notice that their blood ketone levels will slowly drop over time. This drop in blood ketone levels may be seen as the ketogenic diet isn’t “working” for them anymore, but if they also measure their blood glucose levels, they will notice that their blood glucose levels are also dropping and that the lower blood ketone levels are most likely due to their body becoming more efficient with ketone formation and not that the keto diet no longer works for them.

How to calculate your Glucose-Ketone Index or GKI

The Glucose-Ketone Index calculation is a ratio of glucose (in mmol/dl) divided by blood ketone levels (also in mmol/dl). It’s a simple calculation that’s very helpful in tracking your metabolic response to a low-carbohydrate ketogenic diet.

When to test for Glucose-Ketone Index (GKI)

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. Testing 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.

While the Glucose-Ketone Index was originally designed by Meidenbauer and Seyfried to track compliance on a ketogenic diet for cancer patients, the GKI has been expanded to also include nutritional ketosis ranges.

There isn’t any research I’ve seen yet that validates the GKI for weight loss and nutritional ketosis. However, I think it’s helpful for patients to realize the importance of measuring blood ketones and blood glucose when starting a ketogenic diet. By monitoring both blood values, it’s easier to understand how your body is responding to the ketogenic diet.

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 Glucose-Ketone Index (GKI) number that will be greater than 9. Even with a normal glucose range, high-carb dieters will have either low or no measurable blood ketone levels.

GKI between 6 and 9 – Mild ketosis

Mild ketosis, with a glucose-ketone index (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 typical 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. Diabetics will also find that they also have an improvement in 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 Glucose-Ketone Index (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, cancer cells require glucose to function. Dietary treatments for several types of cancers focus 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.

While Meidenbauer and Seyfried published their ketogenic diet and cancer study on patients with brain tumors, there have been subsequent studies looking at the ketogenic diet as an adjunct therapy for other types of cancer.

A 2020 study from Japan that was published in the journal Nutrients looked at the effect of a ketogenic diet in patients with a variety of Stage IV cancers and saw some impact and either reduction or resolution of cancers in a portion of the patients that were on the ketogenic diet. These patients were also receiving chemo and/or radiation treatment, so it’s not possible to contribute the improvements completely to the ketogenic diet.

Seyfried also thought that the Glucose-Ketone Index might have usefulness outside of cancer, believing that a very low GKI may also potentially be beneficial for other neurological diseases such as Alzheimer’s, Parkinson’s disease, and traumatic brain injuries. 

How to improve your Glucose-Ketone Index (GKI)

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. Increased 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.

What impacts your Glucose-Ketone Index?

The number of carbohydrates you eat can have the biggest impact on your GKI ratio. Eating more than 50 grams of carbs a day can lower your blood ketone levels while also elevating your blood glucose levels. For a very low GKI, such as in cancer therapies, you may need to limit your total carbohydrates to less than 10 grams a day.

The type of carbohydrates you eat can also affect your Glucose-Ketone Index. Twenty grams of table sugar will raise your glucose levels and GKI quicker than 20 grams of more complex carbohydrates in vegetables. 

Too much protein in some people can also lower your ketone levels and raise your GKI. Some people can tolerate higher levels of protein without spilling into gluconeogenesis from the extra protein, while some people are more sensitive to higher protein intake. You may need to adjust your macros on the ketogenic diet with a higher ratio of fat to protein if you are noticing that you are having a difficult time staying in ketosis on higher protein intake.

Another issue that some people who have been on a ketogenic diet is that they develop “adaptive glucose sparing” or physiological insulin resistance as the body tries to ration the limited blood glucose for the brain and limit the amount of glucose the muscles will take up.

I go into more detail about adaptive glucose sparing in this article.

Exercise, especially either fasted endurance exercise or high-intensity interval training can positively impact your Glucose-Ketone Index by lowering blood glucose levels and increasing your blood ketone levels. I’ve noticed that after a 40 mile fasted bike ride, my ketone levels will jump to 2 to 3 mmol/dl while my blood glucose levels will be in the low 60s.

Finally, any type of stress and illness can have a negative impact on your GKI ratio. Even one night of poor sleep can make you a little more insulin resistant and slightly raise blood glucose levels. So focus on trying to get a good night’s sleep every night as well as trying to decrease the amount of overall stress in your life.

Try our GKI – Glucose-Ketone Index Calculator