What Does Ketosis Feel Like, and How Can You Tell If You're in It?

2020-01-22

In this recording

An eight-minute explainer from January 2020 on the signs of ketosis and the cheapest way to check.

[0:00] Opening joke: it feels like biting into a York Peppermint Patty. Then the real answer: steadier energy, no crash after big meals, no feeling run down until you eat.
[0:43] No blood-sugar spikes and crashes, so no peaks and valleys and no post-lunch nap. Some people also notice they think about food less and aren't hungry at the usual times.
[1:22] Testing: urine strips. Early on you don't use all your ketones, so they spill into urine and the strip reacts.
[1:58] As you adapt, strips can stop showing ketones. That's a false negative: you're still making them, just not spilling them.
[2:30] After adapting, a blood or breath meter will show whether ketones are in your blood. But it only shows ketones in transit, not how much you're making or using.
[3:08] Other signs: early on, your pee, sweat and breath can smell different, because two of the ketone bodies are acetoacetate and acetone.
[4:18] Cost: I said blood strips run up to about a dollar a test, while urine strips are about $7 for 50 to 100. Pennies against dollars.
[4:45] Once you know carb restriction puts you in ketosis, testing becomes a hassle. Most people a year or two in don't test at all.
[5:40] Strip darkness: don't worry about it. Any colour change means ketones are spilling. Darker isn't deeper ketosis or "doing it better".
[6:54] What you're really waiting for is the ability to use ketones, not produce them. That just takes time.
[7:14] Strips in reverse: after they've been dark, they should get lighter over time as you adapt, possibly all the way to negative.

Watching this in 2026

"Use the strips in reverse" at [7:14] is the best idea in this video, and I don't think I'd said it this clearly before. In 2017 I'd explained that strips fade as you adapt (video 8wOheKcBEd8) and that dark strips aren't dangerous or proof of dehydration (video GojQvo_2GS0). Here I turned that into something useful: a strip that goes dark and then gets lighter over weeks is a rough picture of you adapting, not a sign you've failed.

The view on testing is also where I'd landed by 2019, when I said you don't need a monitor and it's probably a waste of time and money (video 1JbK1_ClDmY). In this 2020 recording it's softened into a beginner's tool: cheap strips for the first couple of weeks, then stop.

Correcting one line: acetoacetate is not vinegar

At [3:08] I said acetoacetate is the main ingredient in white vinegar. That's wrong. Vinegar's acid is acetic acid. The names sound alike, but they're different molecules. The acetone half is right: acetone is the solvent in many nail polish removers, and it's one of the three ketone bodies your liver makes, along with acetoacetate and beta-hydroxybutyrate (BHB) (StatPearls, Biochemistry, Ketogenesis). The rest of my explanation of the "keto breath" smell stands.

The claim worth unpacking: why strips fade

The idea that strips fade because you're using ketones rather than making fewer fits the classic physiology. After weeks of fasting, Owen et al., 1967 found BHB and acetoacetate had replaced glucose as the brain's main fuel. Ketones you burn don't end up in your urine.

No study on the evidence pages measures urine-strip colour over months of keto, so "fade as you adapt" is a reasonable inference, not a measured curve. And the point at [2:30], that a blood reading shows ketones in transit rather than production or use, is fair. A blood level is a snapshot of supply minus demand.

When a ketone reading is a medical question

Nutritional ketosis and diabetic ketoacidosis are different states with very different ketone levels (Laffel 1999; StatPearls, The Ketogenic Diet). Everything in this video assumes a person without diabetes. If you have type 1 diabetes, type 2 diabetes on medication, kidney disease, or you're pregnant, ask your doctor what ketone level should make you call, before you start. See ketosis vs ketoacidosis and who should talk to a doctor.

Key points

Ketosis often feels like steadier energy and less hunger. No evidence page measures that directly; it's what I and many others noticed.
Urine strips are a cheap check for the first couple of weeks. Any colour change counts. Darker isn't better.
Strips fading over time is expected as you adapt. You can watch that happen.
Blood and breath meters work after adapting but cost more, and most long-timers stop testing.
Acetone is a ketone body; acetoacetate is not the acid in vinegar.
Diabetes, kidney disease or pregnancy: get ketone guidance from your doctor.

Guide: testing for ketosis · urine strips · blood meters · breath · do you need to test? · what ketosis is · fat adaptation · ketosis vs ketoacidosis
Blog: signs you're in ketosis · strips not changing colour · are dark strips dangerous? · optimal ketone level · why am I not hungry?
Videos: three ways to test for ketosis · dark keto strips · the Men's Health rebuttal