If you've read any diet story in the past year, you've likely seen a mention of the trendy keto diet. While the main goal of the high-fat, low-carb diet plan typically comes down to weight loss, at its core the objective is getting the body to use fat as its primary fuel source.
"The body's preferred fuel is glucose," says Kristin Kirkpatrick, R.D., a registered dietitian at Cleveland Clinic Wellness Institute. "Every cell and especially your brain will draw on it before anything else as a quick source of energy. But when you drastically cut carbohydrates (the main source) and protein is low enough so that the liver does not go into gluconeogenesis (the formation of glucose from amino acids), the body turns to another source of fuel: fat." When your body begins working off fat, rather than carbs, that's when you reach what's known as ketosis. (Related: 8 Common Keto Diet Mistakes You Could Be Getting Wrong)
What is ketosis?
Without glucose as a power source, your body breaks down fat stores into fuel, creating glycerol and fatty acids—these fatty acids then get converted to ketones to deliver energy to the muscles, brain, and nervous system, explains Melissa Majumdar, R.D., C.P.T., spokesperson for the Academy of Nutrition and Dietetics and senior bariatric dietitian at Brigham and Women's Center for Metabolic and Bariatric Surgery. "Instead of using muscle as fuel, ketosis switches the body over to use ketones," says Majumdar. "This spares muscles, allowing for preservation of lean muscle mass." (Related: EverythingYou Need to Know About Keto Flu)
Okay, but how do you know when you've reached ketosis?
What are keto strips?
This is where keto strips come in. They were originally designed for those with diabetes who are at risk for potentially life-threatening ketoacidosis, which occurs when the body overproduced ketones as a result of lack of insulin. This is obviously much different from the ketosis state keto dieters are after.
These days, with the keto diet craze, you can easily find testing strips at familiar retailers such as Amazon (Perfect Keto Ketone Test Strips, Buy It, $8,CVS (CVS Health True Plus Ketone Test Strips, Buy It, $8, cvs.com) for as low as $5.
The strips themselves measure the ketone levels of your urine—more specifically, two of three ketones known as acetoacetic acid and acetone. However, they don't pick up a third ketone called beta-hydroxybutyric acid, which can lead to false negatives, says Majumdar.
How do you use keto strips?
Using them is kind of like a pregnancy test in that it involves your pee. Most keto strips will have directions that tell you to pee in a cup or container and then dip the test strip into it. As for the results, they're similar to what you'd see in school science class when you're testing the pH level of water. A few seconds after dipping the strips in urine, the tip will turn a different color. You then compare that color to a scale on the back of the keto strips package that indicates your current level of ketosis. For example, a light beige means trace levels of ketones and purple equals high levels of ketones. You only need to test your ketone levels once a day. Research has indicated that early morning or after dinner might be the optimal time to use keto strips.
Should you use keto strips?
If you're someone who is driven by numbers and you don't want to guess whether you're in a ketosis state simply based on how you feel, consider trying keto strips, says Kirkpatrick. They can be especially helpful for those just starting the diet and getting familiar with the symptoms. (Keto flu is common among new dieters who aren't used to high-fat, low-carb eating.)
Many people think they're in ketosis and they aren't, says Kirkpatrick. "Either their protein is too high or their carb levels are higher than they think." It's also common to get "knocked out" of ketosis, she adds if you let go of the reigns during a special event, or if you're practicing carb cycling.
It may be beneficial to know where you stand. But because the keto strips leave out that third ketone, this testing method is inherently less accurate than a blood ketone test, which includes a reading of all three ketones. "Measuring all types of ketones will be the most accurate, and if the test strip isn't measuring beta-hydroxybutyrate, the body could actually be in ketosis but the test strip may not indicate it," says Majumdar.
Plus, if you've been following the keto diet consistently for a while, your body will get used to grabbing ketones for energy, which means fewer will be wasted in your urine, therefore making the keto strip testing results inaccurate if finding ketosis is the goal. (Related: Keyto Is a Smart Ketone Breathalyzer That Will Guide You Through the Keto Diet)
What's more, people reach ketosis at different levels of carb intake—it's often less than 50 grams per day, but this can also vary, even from day to day. "Relying on the ketone strips for feedback on intake and not using the mind-body connection can lead to more diet restriction or disordered eating patterns," Majumdar also warns. Without paying attention to how your body feels—which includes how your body "feels" while in ketosis, but also satiety, quality of life, and overall energy—you might miss warning sides of some common downsides of the keto diet. "If you feel worse, these food adjustments may not be a good fit for your body," says Majumdar.
So while there's no immediate danger in trying out the strips, says Kirkpatrick, you don't have to go crazy looking at your numbers. Even if you test frequently, remember to focus on how you feel on any new diet, too.