Are ketone measurements absolute or relative?

[Sascha_Heid]

If ketone measurements are absolute, then an inactive day and an active day might give the same reading while the relative amount was very different.
For example, if you have 10 ketones in your blood they might be sufficient for an inactive day and you are in deep ketosis. But on an active day 10 ketones would only be sufficient for half of your energy requirements. An absolute measurement would give the same reading (10), but a relative reading would be very different (50%).
Then there comes the issue of what the consequences will be if ketone-energy is insufficient and additional energy is required. Will this bring sugar into the game and thus raise insulin and therefore inhibit ketosis? This would make no sense.

[kcfricke]

If you are in ketosis and you need more energy, you will get it from body fat. If you don’t have enough body fat to support your needs, your metabolism will slow down and you will be cold and tired. The reading—blood and breath---- measures what is actually there at that moment. Immediately after exercise, your reading will be lower, because you just used what you had.

[BillJay]

Then there comes the issue of what the consequences will be if ketone-energy is insufficient and additional energy is required.

Ketone measurements would always be absolute in the sense that they are always measuring the ketones present at that time, but relatively speaking, the body could be consuming far more overall, so BK isn’t reflective of the rate of ketogenesis.

In the earlier stage of keto-adaptation, the body in general adapts to burning ketones, but from what we see from Phinney/Volek, subsequent stages involve skeletal muscle switching to burning fatty acids directly which preserves the ketones for the brain which can’t burn fatty acids.

Then there comes the issue of what the consequences will be if ketone-energy is insufficient and additional energy is required. Will this bring sugar into the game and thus raise insulin and therefore inhibit ketosis?

This means that the answer to part of the question is somewhat different based on the stage of adaptation and the rate of energy output relative to the rate of ketogenesis in the liver.

So while the muscles are still using ketones over fatty acids, I think it would be easier to expend more energy than can be produced by the liver via ketogenesis, but after that threshold is reached, the limiting factor is energy expenditure relative to the rate of turning fatty acids in to ATP in the mitochondria.

In the earlier stages where the brain and muscle are both burning ketones, it could be possible that the muscles consume more than the liver an produce, resulting in less being available to the brain, triggering the release of glycogen and/or GNG in order to meet the demands of the brain. What I don’t know is how the additional glucose is interpreted in relation to the release of insulin.

In other words, we know how the body responds to the dietary intake of carbohydrates and protein, but does the increase in blood glucose from glycogen or GNG stimulate insulin to the same degree? I think that answer is yes and insulin release is tied directly to blood glucose, so whether or not this insulin interferes with ketosis would be answered by the demand for glucose at the time.

[Raphi]

If you measure, say 1 mmol/L of the ketone BhB in your blood, you are a measuring the molarity of the solution (in this case blood). Molarity here is made of an ‘absolute’ amount of ketones (1 mol = 602 sextillion molecules!) in a certain volume (1 L in this case). You have an absolute concentration.

If you want to know more about the different ways to measure ketones, what are the advantages/disadvantages, check out http://breaknutrition.com/3-ways-measures-ketones-best/.