Ketones in urine: what they mean, levels chart & how to test
On keto or intermittent fasting, ketones are the signal that your body switched fuels — from glucose to fat. Here's what they mean when they show up in urine, the blood levels chart, and which testing method is worth it.
What are ketones?
Ketones — or ketone bodies: β-hydroxybutyrate, acetoacetate and acetone — are molecules your liver makes from fat when glucose runs low, whether from a very-low-carb diet or from fasting. When your blood carries enough ketones to fuel your body and brain, you're in ketosis.
Ketones in urine: what they mean
On a keto diet, ketones in urine are expected — especially in the first weeks: your body makes more than it uses and excretes the surplus. They also show up after fasting, hard exercise or prolonged vomiting. Outside that context they can be a medical signal: in diabetes (especially type 1), high ketones together with high glucose, thirst and nausea can mean ketoacidosis — that's an emergency. During pregnancy, always mention them to your doctor.
Ketone levels chart (mmol/L)
| mmol/L | Zone | What it means |
|---|---|---|
| < 0.5 | No ketosis | Running on glucose; fat isn't the main fuel yet. |
| 0.5 – 1.5 | Light ketosis | You're in nutritional ketosis — satiety and fat-burning benefits kick in. |
| 1.5 – 3.0 | Optimal ketosis | The range most keto dieters aim for. Higher doesn't burn fat faster. |
| > 3.0 | High | Seen in long fasts; no extra benefit. With type 1 diabetes plus high glucose, seek medical care. |
Values are blood β-hydroxybutyrate. Urine strips don't give comparable mmol/L — they read from 'trace' to '+++', and after keto-adaptation they stop reflecting your real ketosis.
How to measure ketones: blood vs breath vs urine
You don't need to measure to do keto — the diet works the same. But if you like feedback, this is what each method gives you:
| Method | How it works | Verdict |
|---|---|---|
| Blood | Meter with β-hydroxybutyrate strips (finger prick) | The reference: accurate at any stage of adaptation. Strips cost ~$1–2 each. |
| Breath | Reusable acetone analyzer | No pricks, no consumables. Correlates well, but less exact. |
| Urine | Acetoacetate test strips | Cheapest way to start. After keto-adaptation your body wastes fewer ketones and strips fade — even while you're still in ketosis. |
Frequently asked questions
What's the optimal ketone level for fat loss?
Anywhere from 0.5 to 3.0 mmol/L in blood is nutritional ketosis; 1.5–3.0 is considered the 'optimal' zone. Higher readings don't speed up fat loss.
Are ketones in urine bad?
On keto or fasting, no — they're the expected sign that you're burning fat. See a doctor if you have diabetes, high glucose, intense thirst or vomiting, or if you're pregnant.
When should I test?
Always at the same time of day so readings compare: fasted in the morning (lowest) or before dinner (highest). One reading says little — the trend is everything.
Why do my urine strips no longer show ketones?
You're probably keto-adapted: your body now uses ketones instead of excreting them. It doesn't mean you dropped out of ketosis — confirm with a blood or breath meter.
Educational content about nutritional ketosis; not medical advice. If you have diabetes, are pregnant or take medication, talk to your healthcare team before starting keto or interpreting your ketones.
