An important aspect of the Ketogenic Diet is knowing how high your ketone levels are. There are three types of Ketones; beta-hydroxybutyrate (BOHB) which is measured in the blood, acetoacetate (AcAc) which is typically measured in the urine, and acetone which is typically measured in the breath.
- Measuring Acetone in the breath is becoming a good option, and I believe that this is probably the future of ketone measurement. It's an area of rapid development, and it was not available when I performed my Ketogenic Experiment, so I'm still gathering data.
- Measuring BOHB is the most accurate, and it's now practical at home using a similar technique to measuring blood glucose, but it's really expensive at several dollars per test.
- The easiest and cheapest technique is to measure AcAc in the urine using a test strip. However, this approach is too inaccurate to be useful.
1 Measuring Acetone
Main article: Breath Acetone Meters
Acetone levels correlate well with body fat loss, but are also elevated by the Ketogenic Diet, MCT  intake, and exercise even in the absence of weight loss. One study found that a one pound (0.5 Kg) per week fat loss correlated with 1.7 PPM of acetone (67 nmol/L). Each ~40% increase in breath acetone was an additional ∼0.5 Lb (250g) of weekly fat loss.
Breath acetone correlates well (though not linearly) with blood (BOHB) ketone levels. This makes it useful for monitoring the progression of a ketogenic diet, as well as for measuring weight loss. The formula below was developed based on 12 adults consuming Ketogenic meals over a short period:
For Breath Acetone (BrAce) in mmol/L: BOHB = 0.11 * BrAce0.47 - 0.18
Note that the relationship is far from exact (r=0.5 or so.)
Breath acetone levels can vary dramatically, with healthy individuals on a regular diet having less than 1 PPM (parts per million) to 1,250 PPM in patients suffering from diabetic ketoacidosis, which is an extremely dangerous medical condition. The diagram below shows some typical ranges. (As far as I can tell, for acetone, 1 ppm is 39.7 nmon/L.)
The charts below show the results of 12 people who consumed for ketogenic meals every three hours following an initial 12 hour fast. You can see a distinct spike in blood BOHB levels at four, seven, and 10 hours, representing the rise in blood ketones and an hour after each of the meals. The blood AcAc levels rise at four hours and 10 hours, but the pattern is not quite so distinctive. By comparison, breath acetone responds more smoothly, and is less responsive to the changes in BOHB and AcAc. This makes sense given that AcAc decomposes spontaneously to acetone with a half-life of about 12 hours, though enzyme activity may dramatically speed this up. Overall, this is a good indication that breath acetone is a viable way of evaluating underlying blood ketone levels.
Breath Acetone may respond more slowly than blood BOHB to a reduction in ketone levels, but I've found no clear research that tracks both together. One study found levels remained steady for an hour after a high protein meal then dropped over the next 5 hours.
The nearest comparison I could find used a high carbohydrate meal rather than high protein, which would result in a faster rise in blood sugar & insulin compared with high protein. It also used a low carbohydrate diet rather than a fast and is on diabetic patients. This makes it a poor comparison, but shows that in principle at least, breath acetone may be slower to respond than blood BOHB.
1.1 Breathing Patterns And Acetone
Acetone is exchanged mostly in the airways, not the alveoli (the tiny air sacs of the lungs), so your breathing pattern will have a big impact on the acetone concentration in your breath:
- A normal, resting breath (called a tidal breath) will result in only about two thirds the maximum acetone concentration.
- A full breath, breathing in deeply and fully exhaling will result in ~85% of maximum acetone concentration but only at the end of the breath.
- Breathing in and out of a bag for six breaths results in the maximum acetone concentration and the best repeatability. Of course, this is the most uncomfortable method.
- Breath holding for over 60 seconds has no impact on breath acetone concentration.
2 Measuring beta-hydroxybutyrate (BOHB)
BOHB is measured in the blood using a small meter similar to a Blood Glucose Meter. A test strip is placed in the meter and a drop of blood is added. After a few seconds, the meter will indicate the level of Ketones. There are two meters on the market in the US, the Nova Max and the Precision Xtra.
- The ketone test strips for Nova Max are cheaper (around $27 for 10 strips), but less accurate and there tend to be a high number of 'bad' test strips. $18.98 USD at Amazon.com.
- The ketone test strips for the Precision Xtra are far more expensive (around $58 for 10 strips), but better quality. $37.81 USD at Amazon.com.
- The best option I've found is to order the Precision Xtra strips from Canada for $23 for 10 strips. I've ordered from the Ketone Strips from Universal Drugstore many times and I've been pleased with their service. It takes a couple of weeks for delivery, and shipping is $7. Another option is Ebay and search for "Abbott Freestyle Optium ketone", which are from Australia and cost nearer $1/strip.
- You have to draw a drop of blood for this testing, and I'd recommend the Owen Mumford Advanced Lancing Device $8.86 USD at Amazon.com. It's not much less painful than other lancing devices, but every bit helps. I also use the narrow (33) gauge BD Ultra-Fine Lancets $14.14 USD at Amazon.com.
3 Measuring Acetoacetate (AcAc)
AcAc is typically measured in the urine using a test strip, which check for 10 different things in addition to AcAc, including trace blood, hydration status and urine acidity. (It's important to test for trace blood in your urine if you're on the ketogenic diet to detect Kidney Stones early.) The test strips are cheap, costing around $0.20 each. $. at Amazon.com. However, AcAc levels tend to correspond poorly to blood ketone levels. During Ketoadaptation, I've found urine levels can be 4x higher than blood ketone levels, but after adaptation the urine levels tend to drop much lower. Hydration status also greatly affects urine ketone levels, and of the levels you're detecting are based on the urine produced since you last emptied your bladder, so they can be quite delayed. See below for a more detailed look at the problems with measuring urine ketones.
4 My Results
I measured my blood BOHB, urine AcAc (using (KetoAnalysis), and my blood glucose. The charts below show the relationship between the values, with the regression line in blue and the 95% confidence intervals shaded. As you can see, for my readings there is better correlation between blood glucose and blood BOHB than there is to urine AcAc. I tried adjusting for hydration using the Urine Specific Gravity values from the test strips, but this made little difference to the correlation. Multiple regression of blood glucose and urine AcAc to blood BOHB did improve the model to r2=0.73.
5 Problems with Measuring Urine Ketones
In the past the only viable method of measuring Ketones was to use a Urine dipstick, but this is too inaccurate to be useful.
- Urine dipsticks require you to match the color of the test strip against reference patches, so it is not particularly precise. Using image analysis (KetoAnalysis) can help somewhat. (The test strips use a nitroprusside reagent which changes color from pink to maroon. The addition of hydrogen peroxide does not improve the ability of the urine tests to detect BOHB.)
- Worse, there is evidence that the values read from urine dipsticks overestimate the level of ketones in the urine. A study that compared the values from Ketostix with an enzymatic test found the formula "urinary acetoacetate = 0.40(dipstick value) + 0.15" would help correct the overestimation.
- To compound matters further, urine levels do not reflect blood levels of AcAc very well.
- High level of hydration will dilute urine ketone levels.
- Kidney function can change the urine levels as the kidney will reabsorb AcAc. With starvation ketosis, the kidneys increase the reabsorption over time, with one study showing a progression of AcAc reabsorption from 47 (+/-10) mumoles/min on day 3 to 106 (+/-15) on day 10, 89 (+/-10) on day 17 and 96 (+/-10) on day 24. Most studies demonstrate no maximum reabsorption rate.
- There is also a time delay if the blood levels are changing, this will not be reflected in the urine levels immediately.
- A study indicated that the level of urine AcAc and blood AcAc vary in a non-linear manner, following the equation "y = 0.3x0.6 + 0.07" (after correction), but r2 was only 0.59 .
- Further problems arise because the levels of AcAc can be quite different to BOHB levels, as shown below. A study of children using the Ketogenic Diet for epilepsy showed that when blood BOHB levels are over 2 mmol/l, urine AcAc dipsticks indicate levels of 80-160 mmol/l.
- Finally, false positives can occur for a number of reasons.
- Pigmented urine (trace level only).
- Vitamin C.
- Low urine pH (acidic).
- Increased urine specific gravity.
- Phenolphthalein (a laxative used in many preparations under various trade names).
- The amino acid L-dopa.
- Drugs, including
- Fever or burns.
6 See Also
- The classifications and types of Low Carbohydrate Diet.
- An introduction to the Ketogenic Diet.
- My experiences with ultrarunning on the Ketogenic Diet
- How the Ketogenic Diet can be used for the treatment and management of disease.
- Health Risks of the Ketogenic Diet
- The time frame and changes that occur with Ketoadaptation
- What are Ketones
- How to measure Ketones
- What ketone levels to aim for
- The pros and cons of the Ketogenic Diet for athletes
- The Types of Ketogenic Diet
- My Ketogenic Recipes
- Non-Ketogenic Low Carbohydrate Diets
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