What is the glucose ketone index (GKI)?
June 10, 2026 · 3 min read
The glucose ketone index, or GKI, rolls your blood sugar and your ketones into a single number. It comes up in keto circles as a "how deep am I" metric, but it was built for a specific clinical purpose, and for everyday keto it's more precision than the goal requires.
The formula
GKI is your blood glucose divided by your blood ketones, both measured in mmol/L. If your glucose meter reads in mg/dL, divide that figure by 18 first to convert it. For example, glucose of 90 mg/dL is 5.0 mmol/L; with ketones at 1.5 mmol/L, the GKI is about 3.3. A lower GKI means your ketones are high relative to your blood sugar. Calculating it needs both a blood ketone meter and a glucose meter.
Where it came from
The GKI was introduced by Thomas Seyfried's team at Boston College in a 2015 paper in Nutrition & Metabolism, as a tool to monitor ketogenic metabolic therapy in brain cancer. They proposed GKI values approaching 1.0 as the therapeutic target in that clinical context — a deliberately demanding level reached under medical supervision, not a casual goal. The source paper sits in the ketone-testing research.
Do you need it for keto?
For weight loss or general keto, you almost certainly don't need GKI. The low therapeutic targets come from cancer and epilepsy protocols, not from dieting, and reaching them means pushing blood sugar very low, which isn't a goal healthy people should chase on their own. Staying in ordinary nutritional ketosis — blood ketones over 0.5 mmol/L — is enough for the usual reasons people do keto. The testing overview covers the simpler ways to check.
A safety note
Chasing a very low GKI means deliberately driving blood glucose down and ketones up, which can be risky without supervision — especially for anyone on blood-sugar medication, where it raises the chance of hypoglycemia. If you take blood-sugar medication or manage a medical condition, talk to your doctor before targeting a specific GKI. Therapeutic ketosis for a medical condition is not a target to self-prescribe. This is general information, not medical advice.
Frequently asked
What is a good GKI number? It depends entirely on your goal. For general keto there's no need to track it; the therapeutic target of around 1.0 or below comes from clinical cancer protocols (Seyfried, 2015), not weight-loss dieting.
How do you calculate GKI? Divide blood glucose by blood ketones, both in mmol/L. Convert a mg/dL glucose reading to mmol/L by dividing it by 18 first.
Do I need GKI to lose weight on keto? No. Plain nutritional ketosis (blood BHB over 0.5 mmol/L) is enough; GKI adds complexity that weight-loss keto doesn't require.
Copper Keto Companion tracks your net-carb input from a spoken meal, so you stay in nutritional ketosis without needing to compute GKI at all.