Keto made easy

Why Did My Keto Strips Stop Turning Purple?

Quick answer: If you've been eating low carb for a while and your strips have faded, the likeliest reason is that your body has got better at using ketones, so fewer spill into your urine. KetoDick says strips spill fewer ketones the more fat adapted you are, and that by month three to six some people test negative while definitely still in ketosis (videos 8wOheKcBEd8, GojQvo_2GS0). A faded strip is not, by itself, a sign you did something wrong.

In this article

Strips measure the spill, not the supply

Urine strips detect acetoacetate, one of the three ketone bodies. KetoDick's word for what ends up in urine is a "spill": ketones that weren't used and left with the water. It's there by accident, not by design (video 8wOheKcBEd8).

Picture a new kitchen tap fitted too big for the sink. In the first weeks, the liver is turning out ketones and the rest of the body hasn't caught up, so the overflow goes down the drain where the strip can see it. Over the following weeks the body gets better at using what's made. Same tap, less overflow.

That's why the strip can go from deep purple in week two to barely pink in month three without anything being wrong. In his words, the more fat adapted you are, the fewer ketones spill at the same level of ketosis (video 8wOheKcBEd8).

Three reasons a strip fades

Reason What's happening Does it need fixing?
You've adapted Less acetoacetate spills because more of it gets used No
Your urine is dilute The same ketones spread through more water read lighter No; check you're not overdoing water
Carbs crept back in Ketone production has actually dropped Maybe, if your goal needs it

The first is the one KetoDick talks about most, and it's the common one if you've been steady for a month or more. The second follows from his point that strip colour reflects your urine, not your blood (video 8wOheKcBEd8). The third is real too, and it's the one people jump to first.

How to tell which one it is

So what you do is ask a few plain questions before you blame yourself:

  1. How long have you been at it? If you're past the first month and the fade was gradual, adaptation is the obvious suspect.
  2. What colour was the urine? If it was clear, you were probably very hydrated and the strip had less to show.
  3. Did anything change in what you eat? A new packaged "keto" snack, a sauce, a habit that crept back. Fading that comes on suddenly after a change is more likely carbs. The guide's page on hidden carbs is the place to look.
  4. How do you feel? If hunger is still quiet and energy is steady, that tells you more than the strip does. KetoDick says the main thing keto helps with is the lack of hunger (video DoSUgIr2rNo).

KetoDick suggests strips are still handy for exactly question 3: confirming keto processes are running when you suspect hidden carbs (video 8wOheKcBEd8). One positive strip after a negative streak can settle a worry. A negative one, after months, mostly can't.

Should you switch to a blood or breath meter?

That's what many long-term people do, he says. Urine strips work poorly after a couple of years, and blood meters are more accurate at that stage (videos 8wOheKcBEd8, GojQvo_2GS0).

The catch is cost. In his 2017 figures, urine strips ran roughly 7 to 15 cents a test, while blood ketone strips were about $3.50 each (video 8wOheKcBEd8). Back-of-envelope: one blood test a day at his figure is about $105 a month. Those are his prices from that year, not today's; the point is the gap, not the exact number.

Before you spend it, ask what you'd do differently with the number. If the answer is "nothing," you don't need the meter. The guide compares blood meters and breath meters, and asks whether you need to test at all.

What the research says

The physiology supports the "spill" picture in outline. The liver makes acetoacetate, beta-hydroxybutyrate and acetone in its mitochondria, under the control of insulin and glucagon (StatPearls, Biochemistry, Ketogenesis). Ketones are then used as fuel by other tissues, a process reviewed in detail by Puchalska and Crawford (Puchalska & Crawford 2017).

The body's shift toward ketones takes time. In a classic fasting study, after weeks without food, beta-hydroxybutyrate and acetoacetate replaced glucose as the brain's main fuel (Owen et al. 1967). That's fasting, not a keto diet, so it doesn't give you a keto timeline. It does show the switch is something that develops over weeks rather than overnight.

On testing itself, Laffel's widely cited review covers blood and urine ketone monitoring, written for diabetes care (Laffel 1999). The evidence pages here don't include a study tracking urine strip colour over months on a weight-loss keto diet, so the "fading" pattern rests on KetoDick's explanation and the general physiology rather than a direct trial.

KetoDick's take

His view on strips shifted. In 2017 he called urine strips a cheap way for beginners to see whether keto processes are going on, and useful biofeedback (videos GojQvo_2GS0, 8wOheKcBEd8, DWI8qQl5BbY). Even then he said you don't need any of the meters to achieve ketosis (video 8wOheKcBEd8).

By 2019 he went further: you don't need to check your levels with a device, ketone monitors are optional, and ketosis isn't the goal, low carb is (video 1JbK1_ClDmY). Read together, that's a sensible arc. Strips help when you're learning. Once you know what you're doing and your appetite is behaving, a faded strip is just the tool aging out.

If you have diabetes or kidney concerns, your testing plan is a conversation with your doctor, not this post. See are dark ketone strips dangerous? for why he splits his advice that way.

Key takeaways