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Biochem Geeks: Question about Gluconeogenesis/Glycogenolysis

Answered on August 19, 2014
Created July 10, 2012 at 3:48 PM

Hey there,

I like to think I've learned a fair bit amount human metabolism, and yet there's something I don't quite understand.

How, exactly, does a "sugar crash" or low blood sugar work in people eating the SAD?

Here's my thinking:

Let's assume these people are full-up on glycogen. (Normally eating lots of carbs and not doing a whole lot of exercise.) If they eat something very sugary/heavy carb, insulin is secreted to get the sugar out of the blood and into into the cells. Sometimes insulin overcompensates and removes too much glucose from the blood, which is when people start to get light-headed, shaky, have cravings, etc., and we usually attribute that to "low blood sugar."

So my question is: if these people are full-up on glycogen, why do they have the crash? Does glycogenolysis not kick in immediately? Is this why? Why would the body perceive this "lack of glucose" when there's actually plenty of it stored up in the liver and muscles? It seems like the breakdown of glycogen should be a lot "easier" than, say, gluconeogenesis from amino acids or glycerol, since glycogen is already glucose, just tons of it all strung together.

I feel like lower-carb people can get fatigued and generally feel crappy after intense workouts b/c they don't have a lot of glycogen reserves.

I hope this isn't a stupid question. Maybe there's something insanely obvious that I'm missing because it's right in front of my face...

1edb06ded9ccf098a4517ca4a7a34ebc

(14952)

on September 07, 2013
at 01:28 AM

@ Dave. the pancreas secretes insulin, which helps transport glucose to where it belongs (in your muscles). If you are insulin resistant, you'll keep pushing out pancreas but the sugar will stay in the blood stream because your muscles are not taking it up.

Fd70d71f4f8195c3a098eda4fc817d4f

(8014)

on July 10, 2012
at 09:24 PM

I'm not saying the glucose won't enter the bloodstream. I was saying that breaking down glycogen (which itself is just long chains of glucose molecules branched and strung together) is not the same thing as turning, say, alanine into glucose. They both produce glucose. It's just semantics. No big deal. (Well, they're different biochemically, but you know what I mean.)

3846a3b61bc9051e4baebdef62e58c52

(18635)

on July 10, 2012
at 07:43 PM

It's a symptom of an unhealthy metabolism. There are people that eat high carb without these symptoms.

3846a3b61bc9051e4baebdef62e58c52

(18635)

on July 10, 2012
at 07:42 PM

It's pretty much as you say....an inability to access energy stores at the most basic level. The particular cascade of hormones and pathology involved you may find in papers like this http://www.ncbi.nlm.nih.gov/pubmed/16306382

510bdda8988ed0d4b0ec0b738b4edb73

(20898)

on July 10, 2012
at 06:11 PM

If you make new glucose from glycogen and then put it in the blood where there's elevated insulin, what's going to happen to the glucose?

Fd70d71f4f8195c3a098eda4fc817d4f

(8014)

on July 10, 2012
at 05:38 PM

But gluconeogenesis and glycogenolysis are different, right? Breaking down glycogen isn't "making new glucose." Still...I can see how insulin inhibits both.

1edb06ded9ccf098a4517ca4a7a34ebc

(14952)

on July 10, 2012
at 04:53 PM

with low blood sugar because your pancreas overshot it's insulin secretion.

1edb06ded9ccf098a4517ca4a7a34ebc

(14952)

on July 10, 2012
at 04:52 PM

Second, I am not a science geek- the last science courses I took were AP bio and AP chem in high school. I think that is how it works though. Gluconeogensis takes time and is a slow process, as humans do not have highly efficient gluconeogensis pathways that felines and other virtually pure carnivorous animals do. So, if you are insulin resistant and you eat a bunch of carbs, your body will pump out insulin but none of the carbs will get into the muscle cells. So, you literally become a sugar burner, and once that sugar is burned (or nearly burners) off, you'll end up...

1edb06ded9ccf098a4517ca4a7a34ebc

(14952)

on July 10, 2012
at 04:48 PM

A couple things. I love that last sentence because people often overlook how redundant and resilient our bodies our. We're so adaptable as a species and can actually thrive on a wide range of macronutrients (provided they are natural, low in toxins, etc).

Fd70d71f4f8195c3a098eda4fc817d4f

(8014)

on July 10, 2012
at 04:45 PM

The more I learn about this stuff, the more amazed I am *anyone* can survive as long as they do eating a ton of refined CHO. It's a testament to how much the human body *wants* to stay alive that it can take so many decades of all-out abuse.

Fd70d71f4f8195c3a098eda4fc817d4f

(8014)

on July 10, 2012
at 04:42 PM

foreveryoung: I think I'm getting it. Insulin levels sometimes stay elevated even after glucose is brought back down, right? So if their BG is back to normal (or actually, lower), but *insulin* is still high-ish, *that* will inhibit glycogenolysis in the liver...so they have low BG *and* no glycogen being broken down. And that's when they reach for a donut...

1edb06ded9ccf098a4517ca4a7a34ebc

(14952)

on July 10, 2012
at 04:41 PM

Yeah, once the glucose is eliminated from the blood stream, which isn't instantaneous. Hence, blood sugar highs and lows.

A968087cc1dd66d480749c02e4619ef4

(20436)

on July 10, 2012
at 04:36 PM

In which case they would not be hypoglycemic...

1edb06ded9ccf098a4517ca4a7a34ebc

(14952)

on July 10, 2012
at 04:34 PM

They'll have high blood sugar while it's being burned off. Once it's burned off they'll have low blood sugar, and will need to eat more bread or pasta or w/e to bring it back up.

A968087cc1dd66d480749c02e4619ef4

(20436)

on July 10, 2012
at 04:32 PM

I was unaware that muscle glycogen had anything to do with blood sugar levels. Isn't that under control of the liver (and pancreas)?

Fd70d71f4f8195c3a098eda4fc817d4f

(8014)

on July 10, 2012
at 04:32 PM

Hmm...good point! But if they don't take up glucose efficiently, they would have *higher* blood sugar, not lower, right?

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3 Answers

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510bdda8988ed0d4b0ec0b738b4edb73

(20898)

on July 10, 2012
at 04:38 PM

Well, as you said there's too much insulin. Insulin works to drive the equilibrium towards storage and away from burning of sugar. So even if you have all the sugar you could use, the presence of insulin virtually locks it away so it can't be used. That's why insulin resistance is so insideous, you have chronically high insulin and can't use your own fuel.

Also, gluconeogenisis is expensive and slow, it's just used as a last resort. It's not just some magic that turns protein in to sugar, it's a fairly complicated set of reactions that your liver has to do, and if your liver is busy metabolizing fructose it might not get to it.

510bdda8988ed0d4b0ec0b738b4edb73

(20898)

on July 10, 2012
at 06:11 PM

If you make new glucose from glycogen and then put it in the blood where there's elevated insulin, what's going to happen to the glucose?

Fd70d71f4f8195c3a098eda4fc817d4f

(8014)

on July 10, 2012
at 09:24 PM

I'm not saying the glucose won't enter the bloodstream. I was saying that breaking down glycogen (which itself is just long chains of glucose molecules branched and strung together) is not the same thing as turning, say, alanine into glucose. They both produce glucose. It's just semantics. No big deal. (Well, they're different biochemically, but you know what I mean.)

Fd70d71f4f8195c3a098eda4fc817d4f

(8014)

on July 10, 2012
at 05:38 PM

But gluconeogenesis and glycogenolysis are different, right? Breaking down glycogen isn't "making new glucose." Still...I can see how insulin inhibits both.

1
A968087cc1dd66d480749c02e4619ef4

(20436)

on July 10, 2012
at 04:29 PM

An over release of insulin (more than is required to bring glucose back to normal) will happen in some people. One of the functions of insulin is to suppress the release of glucose from the liver. Until the insulin clears the blood stream, it will have this effect. if the blood sugar drops too low, cortisol and epinephrine are released to force the liver to release sugar, overriding the insulin signal. The amount of glycogen in the liver doesn't really matter. There is always enough glycogen in the liver - or the brain dies.

1
1edb06ded9ccf098a4517ca4a7a34ebc

on July 10, 2012
at 04:27 PM

There is a mistake in your assumption that, "these people are full-up on glycogen. (Normally eating lots of carbs and not doing a whole lot of exercise)."

They are not full-up on glycogen. They're muscle cells are insulin resistant, so they do not take up sugar efficiently. They're probably perpetually glycogen depleted, and thus on a carb binge 24/7, exacerbating the problem.

People who are insulin sensitive are more efficient at using glucose, so lets say 30g of glucose taken post workout in an insulin sensitive individual, and 29g will go to muscle glycogen replenishment. For an insulin resistant person, maybe only 5g will, and the rest will just wreak havoc in the blood stream until it is burned off. Then once it's gone, they eat more sugar because none of it actually got into the muscle cells. That is a sugar burner. Not whatever the heck Mark Sisson says it is.

If you are insulin sensitive ingested glucose goes towards refilling glycogen stores (and 400g is a lot of room for glucose), while free fatty acids go to fueling your resting activities.

1edb06ded9ccf098a4517ca4a7a34ebc

(14952)

on September 07, 2013
at 01:28 AM

@ Dave. the pancreas secretes insulin, which helps transport glucose to where it belongs (in your muscles). If you are insulin resistant, you'll keep pushing out pancreas but the sugar will stay in the blood stream because your muscles are not taking it up.

1edb06ded9ccf098a4517ca4a7a34ebc

(14952)

on July 10, 2012
at 04:52 PM

Second, I am not a science geek- the last science courses I took were AP bio and AP chem in high school. I think that is how it works though. Gluconeogensis takes time and is a slow process, as humans do not have highly efficient gluconeogensis pathways that felines and other virtually pure carnivorous animals do. So, if you are insulin resistant and you eat a bunch of carbs, your body will pump out insulin but none of the carbs will get into the muscle cells. So, you literally become a sugar burner, and once that sugar is burned (or nearly burners) off, you'll end up...

1edb06ded9ccf098a4517ca4a7a34ebc

(14952)

on July 10, 2012
at 04:48 PM

A couple things. I love that last sentence because people often overlook how redundant and resilient our bodies our. We're so adaptable as a species and can actually thrive on a wide range of macronutrients (provided they are natural, low in toxins, etc).

A968087cc1dd66d480749c02e4619ef4

(20436)

on July 10, 2012
at 04:36 PM

In which case they would not be hypoglycemic...

1edb06ded9ccf098a4517ca4a7a34ebc

(14952)

on July 10, 2012
at 04:53 PM

with low blood sugar because your pancreas overshot it's insulin secretion.

1edb06ded9ccf098a4517ca4a7a34ebc

(14952)

on July 10, 2012
at 04:34 PM

They'll have high blood sugar while it's being burned off. Once it's burned off they'll have low blood sugar, and will need to eat more bread or pasta or w/e to bring it back up.

Fd70d71f4f8195c3a098eda4fc817d4f

(8014)

on July 10, 2012
at 04:45 PM

The more I learn about this stuff, the more amazed I am *anyone* can survive as long as they do eating a ton of refined CHO. It's a testament to how much the human body *wants* to stay alive that it can take so many decades of all-out abuse.

Fd70d71f4f8195c3a098eda4fc817d4f

(8014)

on July 10, 2012
at 04:42 PM

foreveryoung: I think I'm getting it. Insulin levels sometimes stay elevated even after glucose is brought back down, right? So if their BG is back to normal (or actually, lower), but *insulin* is still high-ish, *that* will inhibit glycogenolysis in the liver...so they have low BG *and* no glycogen being broken down. And that's when they reach for a donut...

Fd70d71f4f8195c3a098eda4fc817d4f

(8014)

on July 10, 2012
at 04:32 PM

Hmm...good point! But if they don't take up glucose efficiently, they would have *higher* blood sugar, not lower, right?

1edb06ded9ccf098a4517ca4a7a34ebc

(14952)

on July 10, 2012
at 04:41 PM

Yeah, once the glucose is eliminated from the blood stream, which isn't instantaneous. Hence, blood sugar highs and lows.

A968087cc1dd66d480749c02e4619ef4

(20436)

on July 10, 2012
at 04:32 PM

I was unaware that muscle glycogen had anything to do with blood sugar levels. Isn't that under control of the liver (and pancreas)?

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