Nutritional ketosis is achieved when there are levels of ketones in the blood, breath, or urine. So it makes sense that measuring ketones is the standard way to figure out whether you’re in ketosis. It’s not the only way, through—which I’ll get to in a moment. But first, a quick clarification: although we often use the terms interchangeably, there’s actually a difference between being fat-adapted and being in nutritional ketosis. When you’re fat-adapted, your body prefers fat to glucose. It has ramped up the enzymatic processes it needs to burn fat as energy and feel comfortable doing so. Once you’re fat-adapted, it’s possible to slip in and out of ketosis while remaining fat-adapted.
When you’re in ketosis, your body is creating moderate levels of ketones by burning fat. So how can you be in ketosis without being fat-adapted? If your body isn’t used to burning fat, it still prefers glucose as an energy source—even if there are ketones circulating in your blood because it has to burn fat. You’re only fat-adapted once your body has made the switch to prefer fats. Here’s one way to think of it: after being in ketosis consistently for three to five days, your body may be in ketosis, but it has yet to become fat-adapted. After three to five weeks, your body will be in ketosis and has probably become fat-adapted.
Having a carb-up, for instance, may reduce the level of ketones in your blood for a brief period, but it won’t change the fact that your body prefers burning fat to burning glucose. As we discuss how to determine whether you’re in ketosis, keep in mind that you don’t have to worry about testing, monitoring, or tracking in order to achieve ketosis. If you’re eating a lot of fats and few carbohydrates, you will likely get into ketosis just fine. But it can be helpful to know your numbers when you’re working toward ketosis for the first time.
Testing for Ketones
Ketone bodies can be found in your urine, breath, and blood, and there are instruments for measuring levels of ketones in each. Each tool measures a different type of ketone body. Testing isn’t strictly necessary, but it can be helpful. When I started out on keto, I tested my blood ketones once per day at various times of day, recorded my results, and made a hypothesis each time about why my ketone level had increased or decreased. I did this for thirty days, which was enough to collect a bunch of ideas about what increased and decreased my ketone level. I don’t test my ketones anymore because I know what nutritional ketosis feels like. When I’m on the mark, I’m good to go. When I don’t feel it, I know where I fumbled and what to do to get it back—and I have all that information because I tested my blood for those first thirty days.
However, it’s worth noting that more ketones don’t necessarily equate to increased fat loss. Say, for example, you eat copious amounts of fat: enough that you’re in ketosis and registering ketones, but too much to allow your body to burn its own fat stores. In this case, dietary fat is the energy source, not your body fat. The most important factors in natural fat loss are appetite balance, metabolic healing, and supporting yourself with positive behaviours.
Tests for: beta-hydroxybutyrate
Testing the blood for ketones is the most reliable and accurate approach. It’s also the most expensive. The reusable meter costs about £28, and the one-use test strips range from £1 to £4 each. If you test twice daily, that’s up to £240 a month just for test strips, not including the cost of the meter. My favourite blood ketone meter is the Precision Xtra Blood Glucose & Ketone Monitoring System from Abbott, available at most drugstores. It lets you test both your blood glucose and ketone levels at once. When you measure your blood ketones, you’re looking for a result of 0.5 to 3.0 mmol/l—any number in this range means that you’re in ketosis.
There is no need to go higher than 3.0 mmol/l; when my clients have a number higher than 3.0, it’s often because they are not eating enough food or they’re dehydrated. If you’ve tested in the morning, before eating, and your ketones have been above 3.0 mmol/l for a couple of days, please eat and/or drink more! You know that you’re in ketosis when your number is between 0.5 and 3.0 mmol/l. Your body is producing significant levels of ketones by burning fat. You know you’re well on your way to becoming fat-adapted when your numbers have consistently been between 0.5 and 3.0 mmol/l for three to five days.
If you’re interested in starting a carb-up practice, it’s generally best to wait until either your ketones have registered between 0.5 and 3.0 mmol/l for five to seven days or you’ve been following the Classic Keto Fat Fueled Profile for ten to fifteen days, whichever happens later. Often these two things happen at around the same time.
Tests for: acetone (resulting from the breakdown of acetoacetate)
Testing the breath for ketones is reliable for most people, much more cost-effective than blood testing, and far more accurate than using urine strips. The best reusable ketone breath meter is made by a company called Ketonix. Their meter can be used multiple times and doesn’t require extra strips; it’s a one-time cost of £149 to £169, depending on the model you choose. To test, you simply breathe out naturally at a slow and steady pace for fifteen to thirty seconds. The tool will take a couple of moments to register a reading, flashing different coloured lights. The key to the success with the Ketonix meter is, when you first purchase it, to sit with it for about an hour and take a measurement every fifteen to twenty minutes, until the values are within the same range.
This lets you work on your testing technique: how you blow into the device makes a difference in how the results are interpreted, so developing a technique and sticking to it will ensure that you’re comparing apples to apples each time you test. Note that your blood and breath ketones will likely not correlate because breath ketones can be influenced by many factors, such as water and alcohol intake. A Ketonix Breath Ketone Analyzer indicates the level of ketones present by displaying a colour: blue for no or very little ketones, green for trace amounts, yellow for moderate amounts, and red for high amounts. The newer models also indicate the level of ketones within each colour by flashing from one to ten times. For example, it could flash ten times with a green light; that means you’re at the high end of the trace group, one flash away from being in the yellow group (moderate amounts).
Tests for: acetoacetate
Testing the urine for ketones is the least accurate testing method. The problem is that it only detects excess ketone bodies that are excreted through the urine. As you continue to become keto-adapted, your body will likely become more efficient at using ketone bodies and therefore won’t excrete as many into your urine. When this occurs, you may experience a drop in urine ketones, but if you measure blood or breath ketones, you’ll see that you’re still in ketosis. If you decide to test your urine for ketones, the presence of ketones is indicated when the test strip changes colour.
The darker the colour, the higher the ketones. The strips group levels together into the trace, small, moderate, and large. The highest level you can test for with many ketone strips is “large” at 160 mg/dL, and this would result in a deep purple, eggplant colour.
An Alternative to Testing
If measuring your ketones isn’t something you want to spend your time or money on, you can gauge where you are by looking at the signs that you’re fat-adapted. This won’t tell you how many ketones are circulating in your body, but it will tell you if your body is using fat as its preferred fuel—which is a good sign that you’re in ketosis. If you have three or more of the signs listed below, it’s likely that you’ve made the switch and are fat-adapted:
- You can skip meals without getting angry.
- It’s easy to go three, four, or five hours without a snack.
- You don’t get ravenous or crave carbs two to three hours after your last meal.
- You crave high-fat foods over high-carb foods.
- You don’t need carbs to push through exercise plateaus.
- You experience steady energy throughout the day without afternoon crashes.
- Your thoughts seem clearer and more focused.
- You no longer experience keto flu.
If you’re interested in starting a carb-up practice, wait until you exhibit three or more of these signs. Generally, that happens after about ten to fifteen days on the Classic Keto Fat Fueled Profile. If you’ve started your journey with carb-ups right off the bat, say with the Daily Fat Burner Fat Fueled Profile, eliciting these signs can take thirty days or more.