Even if you know all the fundamental principles of reaching ketosis in a safe and effective fashion, without proper tools you’ll be just wandering in the dark. Relying on your luck and an approximate sense of direction, basically.
Measuring your blood ketone levels is much better, this gives you at least some numbers to work with. But there’s a better way.
Today, we’re going to tell you about the most effective (and scientifically backed) way of keeping track of your ketosis.
Ladies and gents, meet the Glucose-Ketone Index (GKI).
The glucose-ketone index (GKI) is a concept first introduced by Dr. Thomas Seyfried, Dr. Joshua Meidenbauer, and Dr. Purna Mukherjee in their 2015 study on the metabolic therapy of brain cancer.
Basically, GKI is the relation of one’s blood glucose level (in mmol/l) to one’s person’s blood ketone levels (in mmol/l).
The idea behind GKI is simple and elegant: brain cancer cells (contrary to healthy brain cells) cannot use ketone bodies as a source of energy, only glucose. Therefore, by depleting the body of its glucose stores and drastically limiting incoming glucose, it could be possible to ”starve” cancer cells.
Blood glucose levels can fluctuate significantly throughout the day, that’s why the GKI was introduced as a more reliable metric than ketones and glucose measured separately.
The formula of GKI looks like this if the glucose reading is in mmol/L:
GKI = Blood glucose / blood ketones
If you are from the USA, you may get your blood glucose readings in mg/dL instead of mmol/L. If that’s the case, divide the mg/dL number by 18, and then divide the resulting number by your blood ketones level:
GKI = Blood glucose / 18 / blood ketones
The GKI is the best way to measure your ketosis because it’s based on the two most important substrates that define your body’s metabolism.
Glucose is the body’s primary energy substrate when it’s working in a carb-fueled mode. By default, your body strives to get as much glucose as possible to ensure its survival.
Ketones are the body’s ”plan B”: their level goes up only during those time when glucose is scarce or absent.
Being in ketosis means having BOTH high ketones AND low blood glucose. The easiest way to confirm that is by using the GKI.
Step 1: Measure your blood glucose level using a glucose meter with appropriate test strips.
Step 2: If your glucose reading is in mg/dl, divide the resulting number by 18. If your glucose reading is in mmol/l, skip this step.
Step 3: Measure your ketone level using a ketone meter with appropriate test strips.
Step 4: Divide the number you got in step 2 (if your blood glucose reading was in mg/dl) or in step 1 (if your blood glucose reading was in mmol/l) by the number you got in step 3.
Let’s go through a few examples to make sure you got the hang of the process.
Dave found out his blood glucose is 72 mg/dL (step 1). He divided 72 by 18 to convert his mg/dL reading into a mmol/L one, so he got 4.0 mmol/L (step 2). Dave also measured his blood ketones and got 1.2 mmol/L (step 3). Therefore, his GKI equals 4 / 3 = 3.33
Jane measured her blood glucose, which turned out to be 5 mmol/L (step 1). She didn’t divide this reading by any number, since it already was in mmol/L (skip step 2). Then, Jane measured her blood ketones and got 0.5 mmol/L (step 3). Therefore, her GKI equals 5 / 0.5 = 10
Take a look at the table below to learn how to interpret your GKI.
Low ketones High ketones
Low glucose Dangerous starvation Nutritional ketosis
High glucose The body’s usual way of operating Possible ketoacidosis
A GKI of 9.0 or more means you’re not even near ketosis. Your body is carb-fueled, as usually, and you still have a long way to go.
A GKI between 6.0 and 8.9 indicates light ketosis. This range is good if your primary (or only goal) is to lose weight.
A GKI between 3.0 and 5.9 is the optimal range to reap all the benefits of nutritional ketosis, from weight loss to diabetes management.
A GKI below 3.0 is usually pursued for therapeutic purposes. This is the optimal range for the treatment of cancer, seizures, and so on.
Our man Dave in the example above has a GKI of 3.33, which is perfect if his goal is to get the most out of his keto diet experience.
On the other hand, Jane’s GKI of 10 indicates he’s not in ketosis at all.
Check your macros. The lion’s share of anyone’s keto success lays in defining (and following) the right macronutrients ratio, day after day, no exceptions. Without this, reaching nutritional ketosis is impossible.
Make sure you’re eating the right vegetables. Contrary to the common misconception, not all vegetables are actually low in carbs. For more information, check out our detailed review of what vegs you can eat on the keto diet.
Increase fat intake. Ketones are formed in the body from fat—either dietary or previously stored. Make sure to eat enough healthy fats every day, so that your body will have enough substrate to create ketones from. If you’re having trouble with meeting your daily fat goal, the easiest way is by adding more olive, avocado, or MCT oil to your diet.
You can only improve those things that you can measure, and ketosis is no exception.
To reach your keto goals faster and more effectively, adopt the habit of measuring the metrics that matter to you. In terms of reaching ketosis, the GKI is the supreme parameter to keep under control. Try it out and see for yourself!