What’s the Best Time to Test Blood Ketones? (And How Often)

There are several times during the day when you’re going to get misleading readings if you test for blood ketones. And those test strips are EXPENSIVE, so we don’t want to be wasting them.

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To help you avoid unnecessary cost, by the end of this article you’re going to know:-

  1. When you should be testing
  2. When you shouldn’t be testing
  3. And how often you need to be testing in order to get an accurate picture of your ketone levels.

Now I’ve never been a big tester of ketone levels. When I went through my period of rapid weight loss back in 2016, I didn’t check ketones once. I didn’t need to – I was consistently losing weight, and that was my goal.

There is this myth in the “keto diet” world that we should be aiming for high ketone levels all the time. This is simply not true; in fact, it often leads to overconsumption of fat and is counterproductive.

I’ve made a video that deconstructs this myth and you can check that out here… 

Why test blood ketone levels?

A lot of keto websites/YouTube channels etc are sponsored by the manufacturers of ketone meters. I’m not. So, I’m not going to tell you that you should be testing all the time, because it’s just not true.

But testing can be useful, typically for overcoming problems, so if you are testing, then measuring blood ketones is by far the most accurate way to check ketone levels

I know some people find testing really reassures them that they’re on the right track. It provides some sort of accountability to the data.

Also, if, like me, you’re a bit of data geek it can be quite fun to track these things!

But whilst the ketone meters themselves are often relatively cheap, the test strips themselves are still quite expensive.

We don’t want to be wasting them, testing more often than we need to or testing at times of day where we are going to get a misleading reading.

data geek

When not to test

There are several times during the day where you’re going to get falsely low readings.

The first time you should avoid testing is first thing in the morning, and that is due to...

The Dawn Effect/Dawn Phenomenon

This is a normal physiological process that happens in all of us.

In the early hours of the morning your body releases a number of hormones (cortisol, adrenaline, growth hormones etc), and this is part of the body’s normal circadian rhythm.

dawn effect

This promotes the release of glucose into the blood stream, which is to prepare you for the day ahead.

Diabetics may notice a spike in their blood glucose levels if they test first thing in the morning.

Non-diabetics should not see a rise, as the body effectively compensates by releasing insulin.

However, this rise in blood glucose will cause a dip in the production of ketones, so testing first thing in the morning may give you a lower reading than you may have been expecting. It’s all due to the dawn phenomenon.

So the first time to avoid testing your ketone levels is first thing in the morning. Wait at least an hour. 

The second time you should avoid testing is…

Directly after a meal

Even a low carb meal will cause some insulin to be released by the pancreas. It is not uncommon to see a temporary dip in blood ketone levels at this point.

Ketone levels often quickly recover over the next few hours, but not in an entirely predictable way.

As a side note, some people do like to see the effect their meals have on their ketone levels and may test on a schedule such as:-

  • Before the meal
  • 30 minutes after
  • 1 hour after
  • 2 hours after

This can be quite interesting for a data geek like me to see my body’s response (both ketones and glucose actually), but it doesn’t tell us a lot about the longer-term stable levels of ketones that our bodies are achieving. So do it if you’re curious, but not for any other reason.

The third time of day you should avoid testing is…

After exercise

Ketones are being used by the body for energy, and anything that causes them to be used faster, e.g. exercise, will cause a temporary lowering of ketone levels that will misrepresent your longer term levels.

after exercise

Again, by all means test for curiosity, but don’t get disheartened.

So when, and how often, should you test?

I recommend that the best time of day to test is before main meals, typically lunch and dinner. For me, that is usually 12pm and 7pm, as my habit is to do 16–8 fasting .

how to measure ketones

Check Before Lunch

This gives plenty of time for the dawn phenomenon to pass – and I typically work out in the morning too.

If you normally skip breakfast (like many low carbers do) then it will have been approximately 16 hours since your last meal. If you’ve not achieved a stable level of ketones by this time, you’re not in ketosis.

If I had to test just once a day, it would be before lunch.

Check Before Dinner

There is plenty of time for you to achieve stable ketone levels after lunch, but not if you’ve just exercised.

You may wish to consider testing before bed (if for example you often work out before your evening meal).

Twice a day will give you a good idea of whether things are stable. Adding in a third testing point won’t really add much to your data set.

In summary

So in summary you’re going to want to avoid testing first thing in the morning, after exercise, and in the hours following a meal.

I recommend before lunch and before dinner, but if you’re going to be testing on a regular basis, you’re going to want to find a pattern that works for you and your particular lifestyle. Just make sure you avoid the common mistakes that I’ve mentioned above. Work out what works for you and stick to it!

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