Contrary to what many recipes and blogs out there would have you believe, it’s not enough to eat lots of fat and very few carbs to take advantage of the health benefits of the keto diet. Going keto isn't just a matter of what you eat; rather, it’s a matter of whether you’re producing ketones, an alternate fuel source your body can tap into when glucose can't be found.
To ensure that all their hard work is paying off, some keto dieters extol the virtues of ketone meters, which measure the number of ketones present in your body. These devices come in three very different forms (and three very different price points).
To uncover the secrets of whether blood, urine, or breath ketone meters reign supreme, we checked in with keto experts (and their answers may come as a surprise).
What are Ketones?
The keto or ketogenic diet is a low-carb, high-fat diet that relies on our body’s ability to get energy from two different sources.
While usually, most people get energy from glucose, it’s possible to reduce the body’s glucose to such a degree that it seeks out another energy source: ketones, which are made in the liver as a byproduct of the breakdown of fats. Ketones are only formed when there is not enough sugar or glucose to supply the body’s needs for fuel, and tend to naturally be made when the body is in a state of fasting, for example, while you sleep.
The keto diet takes a two-track approach to force the body to burn ketones rather than glucose: it deprives the body of its glucose source (in the form of carbs), and also deprives the body of calories periodically, via intermittent fasting. Together, these techniques lead to anti-inflammatory benefits and often to weight loss.
Testing for Ketosis: 3 Types of Ketone Meters
Just cutting carbs and eating fat may not be enough to propel you into ketosis. Some people have a higher carb tolerance threshold than others, and finding your own can be a bit of a process of trial and error.
Drew Manning, the creator of the 60-Day Keto Jumpstart and Fit2Fat2Fit, explains that once your body begins to adapt to using ketones instead of glucose, a transition that can last up to two months, you can begin experimenting with your own tolerances for carbs as well as for protein, using ketone meters as a guide.
Manning recommends, for example, upping your protein by five grams a day, testing daily as you do so, to discover at what point your body is no longer in ketosis; the same test can then be performed for carbs.
“There's no one size fits all approach,” he says, but measuring ketones will help you find out these all-important thresholds.
1. Urine Tests
Three methods of testing for ketosis prevail, the cheapest and easiest of which are strips that measure ketones in your urine.
“For the average person," notes Audrey Christie, MSN, RN, CCMA, Holistic Wellness Practitioner, "urine strips are fine.”
“They’re economical, non-invasive, and rather effortless,” explains Dr. Laurie Steelsmith, author of “Growing Younger Every Day: The Three Essentials for Creating Youthful Hormone Balance at Any Age.”
But according to some experts, this method is far from precise, due to the fact that the strips measure the presence of a single ketone body, acetoacetate.
“Urine tests measure only acetoacetates,” Steelsmith says. “What’s more, results are impacted by hydration, and once you’re ‘keto-adapted,’ you’ll see fewer ketones because your body is burning them.”
Kristen Mancinelli, registered dietitian and author of “The Ketogenic Diet,” goes so far as to say that the urine strips “are not accurate at all.”
“People could be wasting a lot of ketones in the beginning without actually using them,” she says. “So the fact that ketones are coming out in your urine means that you're producing ketones, but are your cells using the ketones?”
Dr. Luiza Petre, a board-certified cardiologist with extensive training and experience in healthy diet and weight loss, notes that "Due to fluctuating base-acid balance and hydration, which affect how the kidneys rid the ketone bodies, the results are usually exaggerated on the dipstick.”
“However,” she continues, “They still are accurate enough to be an effective marker that you are in ketosis. Since it is very inexpensive and portable, it makes this [my] recommended test.”
Try it: Perfect Keto Strips ($7.99/100 strips)
2. Breath Tests
Breath is another way of testing ketones, though this method is limited in the same way as urine strips, in that breath meters also only test acetones.
Shawn Mynar NTP, CPT, RWP, Keto Nutritionist, says that the breath meter is “OK,” though she’s “not totally sold on its accuracy.”
However, she does recommend breath testing over urine strips, which she claims are “super inaccurate.”
Steelsmith is of the opposite opinion, placing breath tests “at the bottom” of her recommendations.
“True, one can do a breath test anywhere," she says. "But it’s costly and limited, in that it only measures acetones.”
Try it: Ketonix Breath Meter ($215)
3. Blood Tests
For many experts, the only sure-fire way to know you’re in ketosis is via a blood ketone meter, which Manning calls “the gold standard” of ketone testing.
“Between blood, breath, and urine ketone tests, the most accurate option and the one that I recommend is blood,” says Catherine Metzgar, Ph.D, RD, an expert of nutritional biochemistry and a member of the health coach clinical team at Vira Health.
Steelsmith agrees, noting that blood tests are far more accurate than either urine or breath in that they measure both acetones and B-hydroxybutyrate (BhB), the most abundant ketone body in the blood and a more accurate indicator of mild to moderate ketosis.
The only downside? These meters are far more expensive than the other two: machines can cost close to $100, and individual strips will need to be used and tossed every time you test.
Christie notes that while she generally recommends blood ketone meters, they can be just as problematic as the urine test, as “’spilling ketones’ in the blood or the urine isn't really a sign of anything other than spilling ketones.”
“It can be an indicator that you are on the right track, but not always,” she continues.
Try it: Precision XTra Glucose and Ketone Monitoring Meter Kit ($85.99)
But... Should You Test Ketones at All?
All of these methods have their weaknesses, and according to our experts, none of them is really necessary for most people.
Our experts note that there are two main cases in which ketone testing is a good idea: firstly, when you are on a keto diet for a specific health issue, for example a metabolic disease like diabetes or as part of a doctor-recommended cancer diet.
“Ketone testing is not something that everyone must be doing religiously,” says Stacy Tucker, nutrition expert and RN with Almeda Labs. “If someone is a diabetic, I prefer them to use a blood glucose meter that has a ketone testing reading built into that.”
Some folks using the keto diet for weight loss or general health may still want to test, however, especially when they're just starting out.
“There are situations in which this level of certainty is integral," says Metzgar. "For example, if you are trying to determine your personal carb tolerance, or what carb-heavy foods cause more of a reaction in your body, the precision of blood testing is the way in which you would answer these questions.”
But Mynar notes that now that she has become accustomed to the keto way of life, she barely tests anymore.
“I think that most people get to that place where they know if it has too many carbs,” she says. “They wake up the next morning and they’re just like, ‘Ugh, not in ketosis today.’ You can kind of tell.”
She recommends testing about once a week for the first three to six months of the protocol.
“After that, I think it may just be if you happen to have strips around you, and you had a bunch of carbs, and you’re curious.”
“I don't do it all the time, maybe once or twice a year, as an experiment,” he says. “Like I did a four-day fast a couple of months ago, and I tested my blood ketones just to see what my levels were during the fast.”
At the end of the day, while a ketone meter can be a helpful tool, the goal with the keto diet is to eventually learn to listen to what your body needs on your own.
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