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Old 02-17-2014, 10:17 AM   #1
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A couple of Sciencey Questions about glucose

I have been reading around a lot, but science is not my strongest subject, so I hope someone doesn't mind spoon-feeding this knowledge to me

What I understand is that, while in ketosis, our bodies have switched from glucose-burning machines into fat-burning machines. When we are using glucose for fuel, our blood is delivering glucose to our cells and muscles. Since we only need so much glucose to fuel the body, we produce insulin to clear the excess glucose from the blood. This is how it is converted and stored as fat (?). I get a little iffy here.

When we are in ketosis, however, we are burning fat, instead of glucose, right? But, our bodies still maintain a normal blood glucose level -- not a low one. During ketosis, low blood glucose levels are still dangerous, which must mean that we are using glucose for some purpose.

My question is, why, when we're in ketosis, do we still need a certain level of glucose in our bloodstream, and what function does it serve if it is not being used for fuel?
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Old 02-17-2014, 09:06 PM   #2
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I believe glucose nourishes the brain in the form of glycogen. Our body maintains a small glycogen store even when we are in NK for our brains function. If we eat more protein than we need, we add to that glycogen store, and those of us who are sensitive to excess protein, we can end up with excess water retention and feeling icky if our protein intake is too high. I think the excess glycogen is also utilised as fuel if there is too much, and this pushes you out of ketosis until it's used up and the fat burning resumes. I think ( but don't know for sure) that the excess glycogen from protein is more easy to get rid of than the glucose converted from carby starchy foods......

However science is also not my strong point hahahaha.
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Old 02-18-2014, 09:10 AM   #3
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I think that is correct that the brain absolutely requires glucose and that is why we have gluconeogenisis.

I was recently told by my s.i.l. (who was just finishing up her university degree in kinesiology with an minor in nutrition)..... she was adamant that because of the brains glucose needs that carbs were actually essential. She went on to say that gluconeogenisis was not enough to fill the requirement. While my poor brain was struggling to respond in a respectful manner and to a person who was 100% sure of what she was saying, all I could think to say was that I had been in ketosis for a number of years and that meant that I didn't consume more the 17 grams of carbs ever in a day and many days much less and yet I seem to be operating just fine.
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Old 02-18-2014, 09:24 AM   #4
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Thanks, guys.

Here's a good article called "Your Brain on Ketones" that's really informative: Your Brain On Ketones | Psychology Today

Let me see if I can reformulate my question, then: Our brains need some glucose, even if they can use ketones, so some glucose is necessary. Our bodies can make it with the protein we eat and the little carb we allow during keto. (It seems able to make do even during a fat fast, though?)

Despite the fact that we have a very reduced need for glucose -- just a fraction of what we needed before for our brains, now that brains are also using ketones -- why does our blood sugar need to remain in a normal, pre-keto, range? Since I've been in keto, my blood glucose has ranged between 84 and 104. I remember reading on another keto board where someone's blood glucose was in the 50s and all the responses were shocked and incredulous, saying it was too low and dangerous, even impossible. That's what got me wondering about what function glucose is serving if the blood level needs to remain in the same range.
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Old 02-18-2014, 09:41 AM   #5
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It may be that the person was using a different measurement. In Canada a b.g. reading of 5.0 would be just fine. It translates to 90 as is measured in the States. I do think it is like body temperature in that it is regulated in the brain.

It is my understanding that it is the process of gluconeogenisis that provides the glucose in the absence of dietary carbs or excess protein. This wiki article is a pretty good explanation without getting too sciencey.

Gluconeogenesis - Wikipedia, the free encyclopedia

Dr. Emily Deans (author of the article you provided) is really great. I love her approach through nutrition to treat many issues of the psyche.

Last edited by clackley; 02-18-2014 at 09:43 AM..
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Old 02-18-2014, 10:21 AM   #6
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Quote:
Originally Posted by luckymuma View Post
I believe glucose nourishes the brain in the form of glycogen. Our body maintains a small glycogen store even when we are in NK for our brains function. If we eat more protein than we need, we add to that glycogen store, and those of us who are sensitive to excess protein, we can end up with excess water retention and feeling icky if our protein intake is too high. I think the excess glycogen is also utilised as fuel if there is too much, and this pushes you out of ketosis until it's used up and the fat burning resumes. I think ( but don't know for sure) that the excess glycogen from protein is more easy to get rid of than the glucose converted from carby starchy foods......

However science is also not my strong point hahahaha.
Glycogen is the storage form of glucose. It is long, branched chains of glucose molecules chemically bonded together. It is not the form used for fuel, it needs to be broken back down into glucose first.
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Old 02-18-2014, 10:27 AM   #7
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Originally Posted by ilsita View Post
Thanks, guys.

Here's a good article called "Your Brain on Ketones" that's really informative: Your Brain On Ketones | Psychology Today

Let me see if I can reformulate my question, then: Our brains need some glucose, even if they can use ketones, so some glucose is necessary. Our bodies can make it with the protein we eat and the little carb we allow during keto. (It seems able to make do even during a fat fast, though?)

Despite the fact that we have a very reduced need for glucose -- just a fraction of what we needed before for our brains, now that brains are also using ketones -- why does our blood sugar need to remain in a normal, pre-keto, range? Since I've been in keto, my blood glucose has ranged between 84 and 104. I remember reading on another keto board where someone's blood glucose was in the 50s and all the responses were shocked and incredulous, saying it was too low and dangerous, even impossible. That's what got me wondering about what function glucose is serving if the blood level needs to remain in the same range.
Your body is all about homeostasis. Maintaining optimal levels of many, many chemicals in the blood and body tissues. Anytime homeostasis is upset (if a chemical gets too high or too low) your body does what it can to correct that. Insulin and glucagon are the hormones used to regulate blood glucose. There is actually only a very, very small amount of glucose in the blood at any given time. Even if we don't use glucose for fuel for body cells (if we are keto-adapted), we still do need some glucose (IIRC about 50 g/day) for the brain, so that is a big reason we need to maintain blood glucose levels. Also, there are many biochemical processes at the cellular level that require glucose or other sugars, including in glycosylation of proteins, lipids, and nucleic acids (DNA and RNA). Glycosylation is not the same as glycation, which gets negative attention by some bloggers.

Last edited by Mistizoom; 02-18-2014 at 10:31 AM..
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Old 02-18-2014, 10:50 AM   #8
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One more item I forgot - there are cells in the body without mitochondria that need glucose, they cannot use fatty acids or ketones for energy. These include mature red blood cells.
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Old 02-18-2014, 11:55 AM   #9
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Mistizoom, Thank you! This explanation thoroughly answers my question. And thank you also for introducing me to some new terminology, which I'm sure will occupy me on the googles this afternoon.
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Old 02-18-2014, 01:07 PM   #10
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I am now very confused indeed!

I had read somewhere that our brains thrive on ketones.
Glucose is not absolutely necessary.This is the premise of starving cancer cells,since they can thrive only on glucose.cutting out all glucose starves them as in ketogenic diets and fasting.

I have never heard that glucose has to be present in our body.but brains preferred fuel is ketones.The blood sugar is maintained by ketosis or fat being converted to fuel,no?

If I remember correctly ,Atkins DANDR book had a clear explanation on this.
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Old 02-18-2014, 04:36 PM   #11
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Originally Posted by lowcarbella View Post
I am now very confused indeed!

I had read somewhere that our brains thrive on ketones.
Glucose is not absolutely necessary.This is the premise of starving cancer cells,since they can thrive only on glucose.cutting out all glucose starves them as in ketogenic diets and fasting.

I have never heard that glucose has to be present in our body.but brains preferred fuel is ketones.The blood sugar is maintained by ketosis or fat being converted to fuel,no?

If I remember correctly ,Atkins DANDR book had a clear explanation on this.
From The Art and Science of Low Carbohydrate Living by Steve Phinney and Jeff Volek (page 33):

Quote:
Above 1 mM ketones, more than half of the brain's fuel comes from ketones. The rest of the brain's fuel must indeed come from glucose, but this amount (usually less than 50 grams per day) is easily produced endogenously by the liver from 'metabolic left-overs' via a process called gluconeogenesis.

Last edited by Mistizoom; 02-18-2014 at 04:38 PM..
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