Questions about Glycogen


#1

Glycogen – I know there are 2 types, liver and muscle. Beyond that, there is not a lot of easily digested (ba-dum-bum) information about glycogen metabolism outside of dubious ‘bro-science’. Thus I have questions that I can’t quite find the answers to:

  1. Is it true that glycogen can be replenished while on keto? If so then which is restored, liver or muscle?

  2. I have read that muscle glycogen is used during intense exercise. Does it deplete while fasting if you aren’t doing intense exercises?

  3. Is there a preference in the body for creating liver glycogen vs muscle glycogen?

Thanks!


#2

Wait, actually I just found this abstract about glycogenesis in muscles preferred over liver in fasted rats. Fascinating! https://www.physiology.org/doi/abs/10.1152/ajpregu.1980.238.5.R328

May indicate that muscle glycogen gets replenished during keto via gluconeogenesis – but I’m not sure if the brain would suck up most of the glucose needed for glycogen repletion. After all, we have a much higher brain-to-body mass ratio than rats do. :face_with_raised_eyebrow:


#3

yes it can be replaced while in K, and helps you create fuel on the fly during exercise


#4

@Alley Thanks for answering the first question, I assume you are talking about muscle glycogen because you mentioned exercise? Do you know where can I learn more about this? I want to have an understanding deeper than a simple yes or no.


#5

tim noakes, jason fung, https://t.co/DosuuCI3N6


#6

:kissing_heart: :kissing_heart: :kissing_heart: @Alley … would you possibly have any specific links? They both mention glycogen all over the place, but these question are very specific.

(edit) – my bad, you provided a link. Thanks!!

Just now I found this summary of a study of trying to measure glycogen resynthesis for 13 athletic dudes put on a ketogenic diet: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4271644/ . However, it seems to conclude that significant amounts of increased DXA muscle mass coincided only with the reintroduction of carbohydrates, which suggests that glycogen resynthesis wasn’t significant while in ketosis. Can someone disagree based on specific evidence? Thanks.


#7

re look above there is a link


#8

@Alley

re look above there is a link

Yes, I missed it the first time, thank you. Wow, fascinating! This study is awesome – roughly the same amount of glycogen depletion and repletion during and after exercise in high-carb vs low-carb runners. That is a trip!


#9

I found that absolutely fascinating, but not surprising


#10
  1. glycogen is always replenished. when on keto or a low carb diet. some studied show that the level of replenishment is less than when on a high carb due to physiological glycogen 'sparring" due to being fat adapted.

  2. muscle glycogen is only depleted when the demand for energy surpassed the aerobic beta oxidation of fat rate. otherwise muscle glycogen is not used at all unless you exercise above 'zone 2". muscle glycogen cannot leave the muscle cells.

  3. liver glycogen is always replaced first


(Bacon is the new bacon) #11

The process of gluconeogenesis occurs in the liver, according to what I’ve read. As I understand it, the glucose is sent out in the bloodstream for those organs that need it. Muscles take in glucose and store it as glycogen, which cannot then leave the muscle. I have never heard of gluconeogenesis occurring in the muscles.

There is a phenomenon called “physiological insulin resistance” or “glucose-sparring” whereby the muscles, when fat-adapted long enough, fail to take up serum glucose, thus saving it for those organs that absolutely require it. It’s as though they start to say, “Glucose? We don’t need no filthy stinking glucose!” :grin:

Haven’t read the book myself, but I suspect all this is covered in Phinney and Volek, The Art and Science of Low-Carbohydrate Performance.


(Bob M) #12

I recently started looking into this. Here’s a Phinney/Volek study:

Section 3.5 specifically discusses glycogen. This was a study of 20 men, 10 on high carb (HC) and 10 on low carb (LC). The first paragraph of their discussion:

We studied two groups of highly trained competitive ultra-endurance athletes who were well matched in regard to training status and physical characteristics. The main difference was that the LC athletes consumed 6-times less dietary carbohydrate than LC athletes (82 vs 684 g/day) for an average of 20 months. The most notable findings were that compared to HC athletes, the LC keto-adapted runners showed: (1) two-fold higher rates of peak fat oxidation during graded exercise, (2) greater capacity to oxidize fat at higher exercise intensities, (3) two-fold higher rates of fat oxidation during sustained submaximal running, and (4) no differences in pre-exercise muscle glycogen concentrations, the rate of glycogen utilization during exercise, and the rate of glycogen synthesis during recovery. Thus, we show for the first time that chronic keto-adaptation in elite ultra-endurance athletes is associated with a robust capacity to increase fat oxidation during exercise while maintaining normal skeletal muscle glycogen concentrations.

Will have to examine this in more detail.

However, I listened to a podcast (The Keto Answers podcast) with Dr. Cate Shanahan, who worked with the Lakers for a while. She said that the initial theory that muscle glycogen was basically burnt during exercise appears to be incorrect. Instead, it is used to support other metabolic processes.