Why I Stopped Testing my Ketones on a Ketogenic Diet

On measuring Ketones.

Like many people, when I first started a Ketogenic diet in early 2014 I bought the Ketostix and just couldn’t wait to see the color change.

And change it did!

It was neat, and it provided motivation for me to continue.

Eventually, I got a blood meter, a breath meter and spent lots of time (and money) testing ketones. Between a Ketonix Breath Ketone Analyzer, as well as dozens of blood ketone test strips, I’ve probably spent well over $500 testing ketones. The main thing I learned from my extensive ketone testing regimen is that the results vary widely and there’s little application to my goals.

Eventually, I stopped testing and here are several reasons why:


1. Burning fatty acids from fat is the main benefit of a ketogenic diet

On a ketogenic diet, some of the brain’s energetic demand is fueled by ketones, but the heart, muscles, etc. are fueled by fatty acids. Most of the energy we utilize both at rest and at sub-maximal exertion on a ketogenic diet is fatty acid, not ketones. Quoting Dr. Ron Rosedale on chasing ketones at the Keto Summit:

“I don’t want people to have the mindset that it’s the ketones that are the benefit of the diet. They are a beneficial side effect, but the main benefit is that you are burning fatty acids from fat. The more fatty acids from fat you are burning, the less glucose you need to burn. And that’s really where you are getting the benefit…So ketones are great but the term ketogenic diet indicating that the diet is so good because you are generating all these ketones is a misinterpretation of the benefit. The main benefit is that you are burning fatty acids, and as a side effect of burning fatty acids you are producing ketones that your body can burn too!”


2. Urine Ketones aka “peetones” are ridiculous.

This topic has been beaten to death so I’m going to keep it short. Ketones in the urine are often non-detectable post-ketoadaption, resulting in people thinking they are no longer in ketosis when in fact they are just adapting, thus spilling over less ketone, and the Ketostix have outlasted their usefulness. Further, hydration levels are a confounder in urine ketone testing, which can result in a “false positive” and a “false negative.” Additionally, urine ketones measure wasted ketones – those which are being excreted from the body, not those which are actively being utilized. These ketones are not and were not used by brain. How can one verify if the body is using ketones as an energy source if the only ketones being tested are not being utilized as an energy source? Lastly, peeing on sticks is gross.


3. Testing blood or breath Ketones is cost-prohibitive, physically invasive on the body, and readings are highly volatile and don’t correlate well with each other

Blood ketone strips are anywhere from $2-4 per strip, depending on the deal one can find. People who test blood ketones regularly are investing hundreds – if not thousands – of dollars into them. That’s real money! The only breath ketone meter available as of this writing, a Ketonix, runs between $189 and $239 USD, depending on the model. At least with that investment, you only pay once and you can use it as many times as you want. It is still a multi hundred-dollar investment, however, and the correlation is not any better than with blood.

My blood ketone testing results indicate that the number changes up and down substantially. It’s hard to find anything actionable when the number moves around so much. This leads to confusion and the need to test a ton of times to figure out what is actually going on. As I said, however, testing blood ketones is expensive so you don’t want to have to test over and over again. Also, it requires a prick of the finger (and proper sanitization), which isn’t super painful but doesn’t feel great either.

Per Michel Lundel the inventor of the Ketonix:

“Blood ketones and breath ketones do not correlate well with each other. I’ve confirmed this by testing blood and breath side by side. I’ve had high blood ketones but low breath ketones. I’ve had high breath ketones but low blood ketones.”

Which is “right”? Which do I believe? Why the hell does it even matter?

Below is an n=1 comparison I did a couple of years ago comparing blood to breath ketones. An R squared value of .18 is indicative of, at best, an extremely weak correlation.



4. Misinterpretation of the data

Blood ketones tend to be lower in the morning than the evening. So people test at night and have high ketones followed by a test in the morning with lower ketones and think they ate too much protein with dinner. We know this isn’t true from prior work on gluconeogenesis that we don’t need to get into here.

I learned from Mike Julian and Marty Kendall (of Optimising Nutrition Facebook fame!) that if blood ketones are high and breath ketones are low that can mean that ketones are building up in the blood and not being used. What’s the point in having “high ketone levels” if they are not being used efficiently? Many long-term keto-adapted folks I have spoken with have noted low blood ketones but high breath ketones. Perhaps this is a sign of ongoing keto-adaptation but we can’t say for sure because there isn’t data on this. One hypothesis is that low blood ketones with high breath ketones is merely indicative of efficient ketone metabolism. Hardly a bad thing! If someone was only testing blood they might think they are “no longer in ketosis” even though high levels of acetone via the Ketonix indicates high usage of fat for fuel.


5. Not actionable to my goals:

One can gain, lose or maintain their body weight in or out of ketosis. If someone’s PRIMARY goal is weight loss there is zero reason to test for ketosis. Most people trying to lose weight on a ketogenic diet would be better served by taking all of that money, time, and effort put into ketone testing and applying it toward proper foods choices as well as a structured strength training program.


6. Potentially detrimental to my goals:

One of the first things we learn on a ketogenic diet is not to fear ketoacidosis. Ketoacidosis is a condition in which ketones (and potentially blood glucose levels) are VERY high. The reason why most people do not need to worry about ketoacidosis is because insulin moderates ketone levels. In other words, ketones cause an insulin response (confirmed at 3.0mmol/L but suspected to occur below this level). High insulin levels, in the context of a hypercaloric diet, will lead to weight gain. Overeating fat on keto will give you higher ketones, but insulin will respond to keep those ketones in check and the high amounts of fat will go to storage. People can have lower ketone readings from protein but it is more important to eat an adequate amount of protein to preserve lean body mass than it is to have therapeutic levels of ketones.

In summary there is no ketone number I would see that would be actionable enough for me to make a change to my diet. If I lacked the context of both blood and breath testing it’s very possible to misinterpret the data to a point that would be detrimental to my goals.


Sources/Further Reading: