I work out 5 days a week either running or strength training. I recently got a blood ketone meter and am seeing some curious results. Today, I took my levels at 10am after fasting since the night prior. Then I performed an hour of low intensity cardio and strength training. Afterward I then retested my ketones (still fasted) and they fell from 1.5 to 0.3. I would have thought they should go up? Any thoughts?
I found this, which can probably explain it better than I can:
Anaerobic exercise tends to decrease circulating ketones. This is a known fact. On the other hand, aerobic exercise tends to increase circulating ketones. Anaerobic exercise in ketosis that drops blood ketone concentrations also spikes blood glucose.
Now those are the facts. Hard and simple observations. The explanations are a little less certain, but here’s what the best guess currently is:
Anaerobic exercise obviously is fueled by glycogen. Nothing else can burn anaerobically. It seems that for a ketogenic athlete, the body ramps up GNG under anaerobic conditions to start to restore the glycogen. I think this comes from the little bit of glycogen stored “for emergency” (the liver is never fully depleted of glycogen, the body isn’t wasteful and wouldn’t create conditions that are life threatening), but perhaps it comes from the amino acid pool (which is why protein is important to increase on keto when you exercise heavily). Perhaps it’s even the glycogen breakdown creating pyruvate and lactate which are then recycled into glucose via the cori cycle (which this is the most likely explanation of the whole deal, since you’re burning a lot of glycogen doing high intensity stuff).
The other aspect of this whole deal is that when the lactate is used to create more glucose, the glucose enters the bloodstream and provides oxaloacetate for acetyl-coa (the precursor to all ketones) to not be turned into ketones. The body only turns acetyl-coa into acetoacetate when there is no oxaloacetate available. Oxaloacetate is provided by carbohydrate breakdown.
Therefore, with the increase of glycogen oxidation in muscle -> more lactic acid -> more GNG (a good thing for anaerobic exercise) -> ketone production slightly reduced and more ketones going to the brain because your muscles’ GLUT transporters are more sensitive to glucose uptake -> reduced circulating ketone levels.
^ That’s why ketone levels drop for a ketogenic dieter when they do anaerobic exercise.
Additional bonus fact!: The opposite can happen for someone on a high carb diet doing a lot of aerobic exercise -> glucose levels drop and ketone levels increase. Their bodies burn a lot of carbohydrate, even at the lower “fat burning” intensities. This means once all their carbohydrate is burnt up from an hour of running, there is no more oxaloacetate available and the body starts producing ketones. Every now and then someone will pop up here saying “I’m on a high carb diet but I just registered ketones in my urine!!! Am I diabetic?” And 99% of the time they just finished with 2+ hours of endurance exercise.
Thank you. I’m going to have to read that a few times to digest it but it sounds like this is normal
yep, I would have said something like “glucose gets raised when you do exercise, so that smashes down ketones for a bit”. But this is better and more “science-y”.
Anytime insulin raises ketones will drop. An increase glucose will result in an increase in insulin. An increase in cortisol will raise glucose which will raise insulin which will lower ketones, the dawn phenomenon, stress, and exercise…
This is very interesting…can you post link to this source? I’m interested in digging further. Thank for this info!
I have never tested my blood ketones immediately exercise
but i do find that an hour or 2 after exercise my ketone levels rocket the highest reading i got was 4.6mmol
I do boxing workouts.
so bit warming up, then going few round of punching bag and light sparring…
So once we’re fat adapted, we burn ketones during cardio, and glucose during anaerobic exercise aka weights? I wouldn’t have thought GNG was that quick of a process?
You’re correct, GNG isn’t that quick, but we do have significant quantities of glycogen stored in the liver and muscles that buffers the slower rate of GNG unless you really increase the intensity, and there’s also the later stage of adaptation where the muscles burn fatty acids directly as well as the Phinney & Volek claims in The ASLCP that the body conserves glucose/glycogen while fat-adapted in favor of the fat-based substrates like the fatty acids and the ketones.
I’m a bit confused Bill… So is that good or bad?? Because I definitely wanted to burn the keytones as fuel. My keytones increase after working out… so I’m really trying to figure this thing out.
Don’t worry about burning ketones for fuel. The body will burn them when it wants to. The key here is to be burning fat for fuel. How to do this? Eat keto, and become fat adapted. That’s all you have to do.
Got it! Thank you for that. This is my 8th week of keto and I believe I believe I’m fat adapted, however I probably need to search this forum for a post about that because its probably different for everyone.
You’ll be on your way, but perhaps not there yet. There are lots of threads on fat adaption. Here’s a recent one…
Thanks… I’m reading through it now!
I track blood glucose and ketones before and after different activities both fasted and fed…
Remember that ketones are a source of energy similar to glucose. There are several sources of energy: creatine, glycogen, glucose, ketones, fatty acids…
Depending on the type of exercise or exertion, the body will work through each based on a priority… light weight, high reps will consume a different energy than high weight, low reps.
Also, depending on how you’ve trained your body, its ability to generate glucose or ketones will vary as well. So, you have things that use energy like exercise and stress - and you have things that make energy like making ketones or glucose, etc…
When I exert myself on low intensity cardio, sauna, UV, slow & low time under tension (TUT) weightlifting- my body has a preference for using ketones… so that fuel drops faster than I can make more ketones & usually glucose doesn’t change much… however, give it a couple of hours of rest and ketones come back even higher.
For example- ketones are the preferred fuel source for long distance marathon runners and those that train fasted get their bodies used to rapid lipolysis to make ketones and fatty acids. In this case, the body gets used to GNG (gluconeogenesis) from fat: it rips off the three fatty acids and converts some into ketones. The glycerol backbone is turned into glucose or glycogen to feed the obligate glucose using cells like blood, some brain and deep kidney cells. This is because those cells don’t have mitochondria and must use glucose only… every other cell can be trained to use ketones and its a question of training the liver to make enough fast enough.
But if I do HIIT or other fast paced high intensity activities, I see my glucose spike. This is because the body recognizes this as an emergency situation or stressor and responds by giving me a “boost” of fast burning energy. This can come from liver glycogen or GNG of protein (lean mass).
This doesn’t raise insulin because the body only makes what it absolutely must and will not overshoot… so this form of GNG is a controlled response. GNG caused by eating excess protein will cause both a glucose and an insulin spike…
Basically, GNG needed for surge activities like sprinting or HIIT is demand driven - no insulin spike. GNG due to eating excess protein is to protect the body from excess nitrogen and capture the energy on the backbone amino acid structures. That will cause glucose and insulin increase.
But back to high intensity exercise… glucose goes up and ketone production is halted. I usually see my ketones drop slightly too, but nowhere near the same as low intensity.
These are my results after a couple of years … and training during extended fasting. The rate of glucose or ketone production and the sources of those energy metabolites will change over time. You and your metabolism are a function of what you’ve demanded of your body and how you’ve trained it with your behavior.
The best way to think of it is this - eat and act in the way that you want your body to prepare. If you eat and act like a strongman weightlifter- it will work to optimize that. If you eat and train like a marathon runner, it will give you that too… their bodies are NOT the same… even if both are keto.
Well now you have me wondering if I burned off Lean mass
Because that was definitely NOT my goal (long sigh). I’ll figure it out somehow.
Why? Were you doing a lot of HITT?
The other part of the equation is sufficient protein to offset natural catabolism.
No, not a lot of HITT Karim… just about 20 minutes of FASTED cardio and than weights.
I noticed how good I felt after my workouts and THAT is what would prompt me to check my keytones. That’s when I would see that they increased.
When I googled it I continuously saw that while mines were increasing after working out, everyone elses was decreasing
Thats what lead me here
I’m at the point now just trying to Tweak my diet Karim… Especially in that protein area because I definitely don’t want to go overboard. I’m almost scared to eat protein now