Motivated by numbers and data? You’re not the only one. Biometrics like blood glucose (blood sugar) and blood ketones can provide immediate and ongoing feedback for people following a keto diet. The glucose ketone index (GKI) is a simple calculation that can make it easier to understand these numbers.
Individually, blood glucose and blood ketone levels can give you a fair picture of your metabolic health. Still, there are some disadvantages to relying on just one of these. They can both be affected by several factors, like stress, sleep, or how recently you’ve eaten.
The GKI uses these numbers to provide a more useful indicator of your body’s ability to burn fat.
Here’s a guide to the glucose ketone index, how to measure it, and why it matters.
The glucose ketone index (GKI) provides a snapshot of the relationship between your glucose and ketone levels. It helps you determine how “deep” your level of ketosis is. Ketosis is a metabolic state in which your body turns to ketones from fat as its primary fuel source, rather than carbs (* , *).
There are varying degrees of ketosis, and two key factors that affect your level of ketosis are fasting and carb intake (*).
The GKI is one number that helps you determine your degree of ketosis. It’s simply an expression of the ratio between your glucose and ketone levels (*).
The GKI formula is:
(Glucose in mg/dL ÷ 18) ÷ Ketones in mmol/L = GKI
If your glucose reading is already in mmol/L (which is likely, if you’re not in the U.S.), here’s your GKI formula:
Glucose in mmol/L ÷ Ketones in mmol/L = GKI
Many people who follow a ketogenic diet are interested in knowing their level of ketosis. Here are some examples of who may benefit from knowing their GKI:
- Weight loss: GKI can help you determine if your body is becoming more efficient at burning excess fat (*).
- Fasting: GKI can also be used to monitor fasts. For example, you can use GKI to determine when you enter ketosis and to set a target for breaking a fast.
- Insulin resistance: Ketogenic diets may help improve insulin resistance. Checking your own GKI can be helpful in monitoring metabolic health if you have type 2 diabetes, polycystic ovary syndrome (PCOS), or other conditions associated with insulin resistance (* , *).
- Neurological disease: Ketogenic diets have been used for decades, with great success, for neurological disorders like epilepsy. In these cases, a therapeutic level of ketosis is often required (*).
- Cancer: Therapeutic ketosis may also be helpful for certain types of cancer. Typically, a healthcare team will strictly monitor these cases (*).
- Athletic performance: Many athletes are experimenting with nutritional ketosis or supplemental ketones for optimal performance, and GKI may be a helpful tool (*).
- Longevity/overall wellness: Finally, a low level of nutritional ketosis may be optimal for longevity and overall health — so even if you don’t have more defined health goals, you may want to check your GKI occasionally (*).
- Diet and macro composition
- Amount of food you eat in a sitting
- Total calorie intake
- Health status/medical conditions
- How recently you’ve eaten
- How recently you’ve exercised
- Fasting status
- Stress levels
- Sleep quality
- Use of exogenous (supplemental) ketones
- Use of certain medications
With all of these different factors that can affect GKI, it’s a good idea to check your GKI under similar conditions each time.
Ready to calculate your glucose ketone index level? You will need a testing device capable of testing both glucose and ketones, along with alcohol wipes, lancets, and glucose and ketone testing strips.
Ideally, 2–3 hours after eating is the best time to check your glucose-ketone index. Testing too soon after eating, or waiting too long after eating to test, may both affect your results (*).
Here are the steps:
- Follow the manufacturer’s instructions for your testing device to check your glucose and ketone levels. Make a note of them.
- Calculate your GKI using the formula above, or plug your data into a GKI calculator.
- Interpret your results using a chart like the one below.
Glucose Ketone Index Calculator
Enter your blood glucose in (mg/dL) or (mmol/l) *
Enter your your blood ketones *
This table, adapted from KetoMojo, can help you interpret your GKI results: (*)
|9.0 or greater
|Not in ketosis
|N/A — this level indicates that you’re not following a keto diet or only recently started
|Weight loss and optimal health
|Metabolic conditions like type 2 diabetes, insulin resistance, and obesity
|Dietary management/treatment of cancer, neurological diseases, and chronic inflammatory diseases
|1.0 or less
|Highest degree of therapeutic ketosis
|N/A — this level is generally only attainable under strict, medically supervised ketogenic diets
How often should I test my GKI?
According to a 2015 study on using the GKI for brain cancer, GKI should be measured twice daily, and each measurement should take place 2–3 hours after eating (*).
However, glucose and ketone test strips can be costly. If you’re not testing GKI for the management of a severe condition such as brain cancer, you may want to consider testing less frequently.
For instance, if you’re trying to lose weight, taking one GKI measurement per week (on the same day of the week, at the same time, after the same meal each time) can be a helpful way to measure your progress.
How can I lower my GKI results?
Lowering your GKI results can take time. Especially if you’re brand new to eating keto, it may take several weeks for your body to fully shift into a state of ketosis.
Therefore, the most reliable way to lower your GKI results is to consistently stick with a keto diet.
What is the ideal GKI for weight loss?
The ideal GKI for weight loss is anywhere between 3.0 and 9.0. If you have a lot of weight to lose, or have obesity along with other chronic health conditions, you may benefit from a lower GKI level — which indicates a deeper state of ketosis (* , *).
However, if you only have a little bit of weight to lose or no other health conditions, a GKI from 6.0 to 9.0 is a good range.
Glucose ketone index (GKI) can be a helpful tool for determining your level of ketosis.
Depending on your health goals or purpose for following a ketogenic diet, you may want to aim for a milder or more therapeutic level of ketosis.
To calculate your GKI, all you need is a ketone reading and a glucose reading, taken 2–3 hours after eating.
The glucose ketone index is a valuable data point that can help you better understand your metabolic health and track progress toward your goals.