Fructose and muscle glycogen

[Biggerp73]

I remember reading somewhere back in the day that fructose could only be stored as glycogen in the liver and that once the liver was filled (a small organ only capable of holding maybe 50g worth of fructose as glycogen), the rest of the remaining fructose would get converted into fats and released into the blood stream to be either burned as fuel or stored as body fat. This idea led me to avoid eating large quantities of fruits, as I wanted any excess carbs I ate to be glucose which could spike insulin and store as muscle glycogen and didnt want fructose which, I was led to believe, could not do those things, but would only serve to fill liver stores and then would basically act as a dietary triglyceride once the liver was full.

But today I was doing some reading and it appears this was false. From the Gatorade Sports Science Institute:

"In resting subjects, 30-50% of ingested fructose was secreted into the circulation as glucose and 10-15% was stored as hepatic glycogen in the 4-6 h post ingestion (Sun & Empie, 2012). In addition, some 25% was released into the circulation as lactate (Jandrain et al., 1993). Finally a minor portion (~1-10%) of fructose can be converted into fatty acids and triglycerides (TG) in the metabolic pathway known as “de novo lipogenesis” (Sun & Empie, 2012)."

Thus it appears that the majority of fructose is actually converted to glucose and sent into the blood steam to either be burned as fuel or stored as muscle glycogen, while a smaller percentage goes to liver glycogen and conversion to lactate, while a very small percentage, perhaps as little as 1%, gets converted to triglycerides.

If this is true then it means fruits and foods high in fructose would be indeed be good for storing muscle glycogen and would not carry those risks I was led to believe they carried.

So what say you guys? Had you been led to believe that fructose could only be stored in the liver or converted to fat? Or were you aware that a majority of fructose gets converted to glucose and sent into the blood steam where it can indeed become muscle glycogen?

 

[Biggerp73]

Here is the entire article for those interested. It's pretty neat stuff actually.


https://www.gssiweb.org/sports-scie...tive-implications-for-athletes#articleTopic_5

 

[Itachi]

I've heard the same thing that fructose can't be converted to glycogen and stored in muscles.

Here's a bump so we can see more replies and thoughts on this.

 

[IronLion2]

Fructose doesnt require insulin and is taken straight to the brain and liver. Ive seen multiple studies show fat gain from fructose is nearly impossible.

 

[prodaf]

I remember reading somewhere back in the day that fructose could only be stored as glycogen in the liver and that once the liver was filled (a small organ only capable of holding maybe 50g worth of fructose as glycogen), the rest of the remaining fructose would get converted into fats and released into the blood stream to be either burned as fuel or stored as body fat. This idea led me to avoid eating large quantities of fruits, as I wanted any excess carbs I ate to be glucose which could spike insulin and store as muscle glycogen and didnt want fructose which, I was led to believe, could not do those things, but would only serve to fill liver stores and then would basically act as a dietary triglyceride once the liver was full.

But today I was doing some reading and it appears this was false. From the Gatorade Sports Science Institute:

"In resting subjects, 30-50% of ingested fructose was secreted into the circulation as glucose and 10-15% was stored as hepatic glycogen in the 4-6 h post ingestion (Sun & Empie, 2012). In addition, some 25% was released into the circulation as lactate (Jandrain et al., 1993). Finally a minor portion (~1-10%) of fructose can be converted into fatty acids and triglycerides (TG) in the metabolic pathway known as “de novo lipogenesis” (Sun & Empie, 2012)."

Thus it appears that the majority of fructose is actually converted to glucose and sent into the blood steam to either be burned as fuel or stored as muscle glycogen, while a smaller percentage goes to liver glycogen and conversion to lactate, while a very small percentage, perhaps as little as 1%, gets converted to triglycerides.

If this is true then it means fruits and foods high in fructose would be indeed be good for storing muscle glycogen and would not carry those risks I was led to believe they carried.

So what say you guys? Had you been led to believe that fructose could only be stored in the liver or converted to fat? Or were you aware that a majority of fructose gets converted to glucose and sent into the blood steam where it can indeed become muscle glycogen?

Yes yo can eat your fruits quietly

 

[brutus69]

if that was true, road cyclists wouldnt eat nanners.
but they eat tons. tons a nanners.

 

[Kaladryn]

nanners are half fructose and half glucose btw, but I still think you are correct

btw, the liver average liver supposedly holds 100g worth of carbs as glycogen but this may be much higher in athletes (as is muscle glycogen).

Off topic but very interesting info on carb stores in cyclists:

MarathonTraining.com - The Science of Carbohydrate Loading

 

[IronLion2]

if that was true, road cyclists wouldnt eat nanners.
but they eat tons. tons a nanners.

I agree but a banana is I believe 30% fructose 70% glucose, which is some of the highest GI fruit you can find.

I guess I didnt address the muscle glycogen side of the question to OP. Put it this way, if you're brain and liver are depleted of glycogen you're not going to fill out the skeletal muscles optimally.

EDIT: Damnit as always kaladryn beat me to it

 

[G-FLUX]

Look into the rate limiting enzyme for fructose and things will become much more clear

 

[Fit2Serve]

LOL the logic "fructose turns into fat then goes into blood stream.."
what magic made it turn from glucose to a triglyceride? JUST before entering the bloodstream...? thats like saying when a bber stops lifting his muscle turns into fat. riiiiight.

i was biggest and leanest eating fruits. the fact that it fills liver with glycogen first means less sugar is realeased into the blood stream therefore making you less likely to gain fat from fruits. was always my logic.

i dont even have a degree in biology but i'd bet all my money a sugar doesnt turn into a fat in the liver lol
-F2S

 

[johnjuanb1]

I remember reading somewhere back in the day that fructose could only be stored as glycogen in the liver and that once the liver was filled (a small organ only capable of holding maybe 50g worth of fructose as glycogen), the rest of the remaining fructose would get converted into fats and released into the blood stream to be either burned as fuel or stored as body fat. This idea led me to avoid eating large quantities of fruits, as I wanted any excess carbs I ate to be glucose which could spike insulin and store as muscle glycogen and didnt want fructose which, I was led to believe, could not do those things, but would only serve to fill liver stores and then would basically act as a dietary triglyceride once the liver was full.

But today I was doing some reading and it appears this was false. From the Gatorade Sports Science Institute:

"In resting subjects, 30-50% of ingested fructose was secreted into the circulation as glucose and 10-15% was stored as hepatic glycogen in the 4-6 h post ingestion (Sun & Empie, 2012). In addition, some 25% was released into the circulation as lactate (Jandrain et al., 1993). Finally a minor portion (~1-10%) of fructose can be converted into fatty acids and triglycerides (TG) in the metabolic pathway known as “de novo lipogenesis” (Sun & Empie, 2012)."

Thus it appears that the majority of fructose is actually converted to glucose and sent into the blood steam to either be burned as fuel or stored as muscle glycogen, while a smaller percentage goes to liver glycogen and conversion to lactate, while a very small percentage, perhaps as little as 1%, gets converted to triglycerides.

If this is true then it means fruits and foods high in fructose would be indeed be good for storing muscle glycogen and would not carry those risks I was led to believe they carried.

So what say you guys? Had you been led to believe that fructose could only be stored in the liver or converted to fat? Or were you aware that a majority of fructose gets converted to glucose and sent into the blood steam where it can indeed become muscle glycogen?

Good find!
I was taught the same thing that fructose isn’t converted to muscle glycogen but what perplexed me was when i did a tuna/banana diet I got lean fast. I hate tuna so I didn’t last long.

 

[Tomgrass]

For years I was leaning fastest when most of my carbs were fruits.

 

[MR. BMJ]

Fructose is beneficial in smaller amounts, but too much can be detrimental. You have to eat quite a bit of fruit for it to these levels, and as Kaladryn stated, athletes will probably be able to get away ingesting more than sedentary individuals.

Here is an interesting new study (abstract) showing the benefits of co-ingesting fructose with glucose for athletes....which will support the benefit of eating fruit:

https://www.ncbi.nlm.nih.gov/pubmed...GiQiDAEil3u5pPtBEpJvZ50GTojqUvagsycDupjeuBlts

J Physiol. 2019 Jun 5. doi: 10.1113/JP277116. [Epub ahead of print]
Fructose co-ingestion to increase carbohydrate availability in athletes.
Fuchs CJ1, Gonzalez JT2, van Loon LJC1.
Author information


Abstract
Carbohydrate availability is important to maximize endurance performance during prolonged bouts of moderate- to high-intensity exercise as well as for acute post-exercise recovery. The primary form of carbohydrates that are typically ingested during and after exercise are glucose (polymers). However, intestinal glucose absorption can be limited by the capacity of the intestinal glucose transport system (SGLT1). Intestinal fructose uptake is not regulated by the same transport system, as it largely depends on GLUT5 as opposed to SGLT1 transporters. Combining the intake of glucose plus fructose can further increase total exogenous carbohydrate availability and, as such, allow higher exogenous carbohydrate oxidation rates. Ingesting a mixture of both glucose and fructose can improve endurance exercise performance when compared to equivalent amounts of glucose (polymers) only. Fructose co-ingestion can also accelerate post-exercise (liver) glycogen repletion rates, which may be relevant when rapid (<24 h) recovery is required. Furthermore, fructose co-ingestion can lower gastrointestinal distress when relatively large amounts of carbohydrate (>1.2 g/kg/h) are ingested during post-exercise recovery. In conclusion, combined ingestion of fructose with glucose may be preferred over the ingestion of glucose (polymers) only to help trained athletes maximize endurance performance during prolonged moderate- to high-intensity exercise sessions and accelerate post-exercise (liver) glycogen repletion.

 

[Kaladryn]

For optimal absorption, a variety of fast digesting sugars/carbs is optimal since they have slightly different pathways. Fruit is made up of lots of different simple carbs so it may be optiomal for althetic performance.

100g of banana:

Total Carbohydrate 22.8g
Dietary Fiber 2.6g
Starch 5.4g
Sugars 12.2g
Sucrose 2390mg
Glucose 4979mg
Fructose 4850mg
Maltose 10.0mg

 

[Biggerp73]

Interesting discussion so far, guys. Thanks for the input. I did Google the rate limiting enzyme for fructose, but I couldn't find any practical information about it's relevance. I'm mostly interested in how excess fructose can be converted to glucose and released into circulation to become muscle glycogen, but any information on fructose metabolism will be helpful.

 

[IronLion2]

Interesting discussion so far, guys. Thanks for the input. I did Google the rate limiting enzyme for fructose, but I couldn't find any practical information about it's relevance. I'm mostly interested in how excess fructose can be converted to glucose and released into circulation to become muscle glycogen, but any information on fructose metabolism will be helpful.

https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/fructokinase

 

[MR. BMJ]

Interesting discussion so far, guys. Thanks for the input. I did Google the rate limiting enzyme for fructose, but I couldn't find any practical information about it's relevance. I'm mostly interested in how excess fructose can be converted to glucose and released into circulation to become muscle glycogen, but any information on fructose metabolism will be helpful.

It's not cookie cutter, but yes, fructose can be converted to glucose upon consumption by up to 22% to 56% via the hexokinase and phosphoglucose isomerase enzymes. A lot will depend on whether a person is in the fed or unfed state, and a person who is active in my opinion, will also effect these rates.

Actually, here is an article by Brad Dieter, that will answer your questions:
Fructose: Burying the Boogeyman - Science Driven Nutrition

 

[Kaladryn]

Ok guys, I went all out, I googled "conversion of fructose to glucose" and this is what came up on the screen without even having to click on a link:

Under one percent of ingested fructose is directly converted to plasma triglyceride. 29% - 54% of fructose is converted in liver to glucose, and about a quarter of fructose is converted to lactate. 15% - 18% is converted to glycogen. Glucose and lactate are then used normally as energy to fuel cells all over the body.

Shooting from the hip I would say that massive amounts of pure fructose "could" be bad because you may completely fill liver glycogen before muscle glycogen, however liver glycogen will maintain blood sugar and blood sugar will restore muscle glycogen (muscle glycogen can't restore blood sugar or liver glycogen) so even this isn't' really "bad."

Because fructose is only a fraction of the carbohydrates in most fructose sources, I would say all of this is moot.

 

[Elvia1023]

I have researched the science on/off over the years. But regardless and forgetting that I have experimented over the years. I absolutely love fruit so naturally have tried a lot of things. Everyone is different but I have been very lean consuming huge amounts of fruit throughout the day. Plus this isn't low cal fruits such as many berries this is pineapple, grapes, bananas, apples, oranges etc.

Obviously common sense needs to be used such as carb amount and energy balance. But to me you can't pick a better carb source as they are loaded with vitamins, minerals, anti-oxidants etc.

When I am dieting I do limit carb intake so most of the fruits I consume are very low calorie/carb such as blueberries, blackberries, raspberries etc. I have consumed the above berries everyday for as long as I can remember. But I will also add in others things at times. For a long time I had 1 avocado everyday as well.

Now for the rest of the year I also love pineapple, blood oranges, bananas, grapes, pink lady apples (plus a few others), passion fruit etc. I always feel much better mentally and physically when I follow a diet rich in different fruits. You can definitely implement fruit into your diet regardless if you're bulking or cutting. As this thread is highlighting it won't make you fat because your liver is overloaded with glycogen as long as you follow basic dietary rules such as don't stuff your face with tonnes of fruit. Although I will happily take in 100g carbs from grapes post workout

 

[Beti ona]

I do not like fruit if I'm on a diet, I just feel like I'm more hungry for sweets if I have an apple, my favorite fruit. And once I start, I can eat a ton of apples. Of course, it is better to break the diet with fruit than with cakes or white bread.