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Why and When to Test Glucose and Ketones

  • Last updated November 16, 2017

Testing ketones and glucose on the ketogenic diet can be your key to success. Getting into ketosis is not only eating the right types of food in the right portions, it’s also learning which specific foods adversely affect you and then avoiding them, because we all respond to foods differently. There are many foods (especially dairy, alternative sweeteners, alcohol, and prepackaged foods) that can trigger ketone dips or glucose spikes for some people, but not others. But you won’t know unless you test.

Why test ketones on a ketogenic diet?

If you’re on a ketogenic diet and restricting carbohydrates, you are very likely producing some ketones.  But are you in a state of nutritional ketosis where you will benefit the most? And at what level of ketosis are you in? The only way to know for sure is to test, and blood testing is considered the gold standard for accuracy (vs breath or urine).

Getting into ketosis doesn’t happen immediately. It takes your body anywhere from two to seven days to get into ketosis, depending on a variety of factors, including your unique body, health, activity level, and diet.

You are officially in nutritional ketosis at 0.5 mmol/L and you want to stay there or higher for additional benefits.

Learn more about your ketone levels here.

When you first embark on a ketogenic diet, we recommend testing often and also testing for food sensitivities as everyone has a different response to food and carb levels. When testing often, you can sleuth out foods that may kick you out of ketosis and avoid them.

Learn more about testing for food sensitives and bio-individuality here.

After several months of testing, you should have a pretty good idea of what you need to do to stay at your desired level of ketosis. But it’s a good idea to check in with yourself periodically, as most of us tend to get a little more lax when we’re not kept in check by test results. You may also want to see if you can add more carbohydrates or protein in your diet and remain in ketosis by trying out the changes and testing your results.

Knowing your blood ketone levels can be powerful feedback and quite motivating. It provides you with the information you need to make adjustments and meet your goals.

Why test glucose on a ketogenic diet?

Blood glucose levels give you an indication of whether your blood sugar is too low, too high, or just right, which can also affect your ketone levels. Tracking blood glucose is important if you’re managing diabetes or simply striving for optimal health because maintaining healthy glucose levels helps reduce your risk of many common, life-threatening diseases, including diabetes, heart disease, stroke, cancer, Alzheimer’s, and Parkinson’s.

On the ketogenic diet and in general, glucose testing is a good way to identify foods that significantly trigger blood-sugar spikes in your body. Blood sugar changes far more rapidly than ketones (ketones are slow to move and sometimes it’s what happened the day before that affects ketones most).

Generally speaking, you don’t want your blood sugar to spike more than 30 mg/dL after eating, and ideally, your blood sugar should return to baseline (pre-meal) within 2 hours; if it doesn’t, you may be having an insulin response to that food and may want to consider reducing or eliminating it from your diet.  With this knowledge, you can direct your diet away from foods that adversely affect your glucose levels (and also ketones) and more toward foods that work best with your body.

Learn more about what your glucose levels should be here.

When to test glucose and ketones

We’ve found that testing at consistent times each day gives you good baselines or reference points and opportunities for clear comparison as you progress from day to day.

Here are some helpful testing tips:

    • Test before you break your fast each morning to get a good baseline, ideally an hour or two after waking due to the “dawn phenomenon” which is a  normal release of cortisol that helps your body wake and can cause you to have a higher glucose level and lower ketone level than other parts of the day.  To learn more about the dawn effect watch this video.
    • Test before lunch or dinner: for the most insightful ketone readings, test right before lunch or dinner, at least 2-3 hours after you’ve eaten any other food or drink (other than water). It’s important wait 2-3 hours after eating because consumption of almost any food, keto-friendly or otherwise, will cause your glucose to go up and your ketone levels to fall a bit. Thus, testing well between meals ensures you get a truer reading of your progress.
    • Testing before and after a meal to determine food sensitivities: Although we just recommended that you do not test after you’ve eaten, there is one reason you may want to: testing just before a meal or particular food and then 60 minutes and 3 hours afterward is a great way to find out how your body responds to various foods, snacks, and drinks you have consumed. Advanced users may want to add additional tests at 30 minutes and 2 hours. You can learn more about testing for food sensitivities here.
    • When testing for food sensitivities, please note that glucose is a better indication of food reactions because glucose fluctuates faster than ketones. For example, glucose reaches its peak one hour after eating, while ketones take much longer to rise or fall.
    • Remember that exercise also can affect your measurable ketone levels since your body may burn available ketones as fuel. Watch this video to learn more about testing before and after exercise.
    • Keep in mind, with ketones, bigger numbers are not always better. A reading of 4 or 5 isn’t necessarily better than a reading of 1 or 2.  A high reading could mean that your body is very good at producing ketones, but possibly your body isn’t great at using them yet.  Usually once you are fat adapted, you will rarely see those high numbers, unless you are fasting.  So don’t chase higher numbers. Everyone is different, if you are in the zone (ideally 1.0-3.0) you are doing well!

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