I’m trying to think through some questions with regard to the brain and ketones. Anyone have thoughts on the following questions?
Can the brain use ketones and glucose at the same time? (I’m thinking yes b/c the brain always requires a minimal amount of energy in the form of glucose. Correct?)
If both ketones and glucose are available, does the brain prefer one or the other?
Can the brain use ketones if insulin is high (eg exogenous ketones)? Is this different than skeletal muscle tissue?
Is there an adaptation period for the brain to effectively use ketones?
Does the brain use ketones at any level or only when ketones have surpassed some threshold level?
Thanks
amwassil
(Michael - When reality fails to meet expectations, the problem is not reality.)
#2
At work so can’t respond in detail. Others will likely add more detail. My understanding is that the brain can/will use whatever fuel is available, but will use ketones preferably. Ketones burn more ‘cleanly’ than glucose. Insulin inhibits fat burn and consequent ketone synthesis, so ketone availability will vary in response, but I think as long as you stay in ketosis the brain will get the energy it needs from ketones.
Hi @nickdag! I can try and answer some of your questions, those that I (believe I) know. Others will chime and most likely clarify what I muddled lol.
Yes. The brain’s use of fuel can be segmented thusly: 75% ketones, 25% glucose.
Which, coincidentally, matches the ratio in trigs, when used for fuel: 3 parts free fatty acids, 1 part glycerol. Go figure!
Certain parts of the brain require glucose, but most of the brain functions better with ketones. I, too, have been trying to figure out which parts of the brain need glucose. Nothing yet.
I’d think if insulin is high, then no ketones are being produced, so the brain is left with glucose only.
However, if using exogenous ketones then Yes, they will get to the brain and help it to function better/clearer, while the rest of the body is left with glucose for fuel, due to lack of Free Fatty Acids from no fat metabolism.
I have no answers for your last two questions, so I hope other members chime in.
You have a lot of good knowledge in the post but this raises many questions for me. First I am highly insulin resistant and always have higher fasting blood glucose levels (112+) even though I have been eating a fairly strict keto diet for almost a year now because of steroids. I test positive for ketones in my regular lab work (no home testing) and have lost over 50# now and 25% of my total body weight. I am definitely producing ketones and I am in ketosis so I don’t believe your statement is true in my case anyways.
PaulL
(You've tried everything else; why not try bacon?)
#5
Whether the brain actually needs any glucose at all seems to be up for debate. Cahill said it in the sixties, but I haven’t seen any data to support it. Georgia Ede says that certain parts of certain brain cells need glucose, but Benjamin Bikman claims that this assertion is not supported by any data he has been able to find. So who knows?
What is clear is that glucose and β-hydroxybutyrate are metabolised by separate pathways, so I suppose that in theory there is no reason why a neuron couldn’t metabolise both simultaneously, but I have no idea how that works in practice. I do know that insulin is needed for the brain to be able to metabolise glucose, but whether it is needed for ketone metabolism as well is something I don’t know, one way or the other.
Most people report that their thinking is much clearer when their brain is using β-hydroxybutyrate. “Carb fog” and “keto clarity” are terms you will encounter frequently on these forums.
If insulin is too high, it suppresses ketogenesis in the liver, which is the source of the β-hydroxybutyrate used by the brain. However, some people feel that exogenous ketones can be helpful, even if the patient is not in ketosis (for example an institutionalized patient with Alzheimer’s disease, whom the institution is required to feed on the SAD, might still benefit from exogenous ketones), but I don’t know of any studies that have definitively answered this question.
I don’t belive it’s very long, probably as soon as the glucose runs out. The fat-adaptation period for muscles lasts 6-8 weeks, usually, but people report brain benefits earlier than that. My understanding is that every cell that doesn’t specifically require glucose only can manage on ketones, some better than others. Muscles seem to prefer fatty acids even to ketones; fatty acids cannot cross the brain-blood barrier, so they are out for the brain, but the brain seems to do well on whatever; recent research has shown that the heart muscle does exceptionally well on β-hydroxybutyrate.
Good question.
Oh, and by the way, add acetoacetate to the list of ketone bodies that the brain can use. And I believe that even acetone can be used, in a pinch. I suspect that may well be because the brain is essential, so it can operate on whatever it gets.
My ulterior motive for asking these questions is that I often feel unwell on the ~2nd day of a fast or if more immediately if I fast and exercise. I get headaches, lose focus, foggy thinking, fell unhappy, etc.
In a recent example, I was already supplementing sodium, potassium, and magnesium, and I began to feel unwell toward the end of my 1st day of fasting. I decided to try an experiment and eat some MCT oil. Within 20 minutes, my state was drastically improved.
In other cases, I’ve noticed similar symptoms (especially after long, low-grade exercise) that have been alleviated with < 10g sugar.
What this indicates to me is that my brain isn’t getting enough energy in certain situations, and I’m trying to understand why that is.
Is my body not (yet) able to send sufficient fat to my liver for ketogenesis?
Is my liver not keeping up with gluconeogensis?
Are other organs & muscle outcompeting the brain for the ketones or glucose?
