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A synopsis of study about whether glycogen can be stored as fat

Hi all!

There has been much discussion here on whether glycogen can be stored as fat. Curious, I decided to do some research, and I just finished reading this research study on how glycogen is stored as fat.

You can read the study yourselves at the link provided below. But if you’re not inclined, I wrote my own description of the study (very basic description indeed, there is a lot of information unrelated to our question that I didn’t include), and then I followed up with some of the relevant points afterward.  I wrote salient points in bold in case you don't have time to read every sentence. 


For those of you who aren't inclined to read any further, here's the bottom line: Glycogen CAN be converted to fat, but it has to jump through a lot of interesting hoops to get there.  


But please try to read the original study for yourselves, just in case I misread or omitted something. It is not my intention to mislead anyone at all! 

Is this the absolute end of this discussion? I doubt it, since this is only one study. But what I found is that is proves everyone right, more or less! LOL

Glycogen storage capacity and de novo lipogenesis during massive carbohydrate overfeeding in man 

Kevin JAcheson, PhD; Yves Schutz, PhD; Thierry Bessard, MD; Krishna Anantharaman, PhD; 

Jean-Pierre Flail, PhD; and Eric Jaquier, MD 

Accessed at: http://www.ajcn.org/content/48/2/240.full.pdf.

A very simple description of the study:

The experiment lasted for 14 day and involved three men all of similar athletic ability and physique. During the first three days, the subjects glycogen stores were depleted to near zero; then from days 4 through 12 (9 days in all), the subjects were overfed on a high-carbohydrate, low-fat diet. Approximately 3600 extra carbohydrate calories per day were needed to produce an overfeeding condition. Subjects also exercised twice a day (30 mins each time) and they could do additional exercise, but they were not allowed to do any anything strenuous (other than the two assigned workouts). It took approximately 4 days for the subjects’ glycogen stores to be filled, but it was after day 2 that glycogen began converting to fat (this was once their glycogen storage sites had reached a minimum level of 500 grams of glycogen). By the end of the overfeeding period (9 days), the three subjects gained on average 4.6 kg. Of that it was calculated that 2.84 kilos was water weight (glycogen requires 2-4 times the amount of water for storage), 665 grams (about 1.5 lbs) was muscle growth, and the remaining 1.1 kilos was fat. Subjects weights returned to their beginning weights two days after the overfeeding period.


Definition: de novo lipogenesis: conversion of glycogen to fat

Here are some of the interesting findings of this study.

1. When overeating on carbs the first thing that is done with the excess glycogen is to fill glycogen storage sites in the muscles and liver


2. According to the discussion provided in this research, it is pretty hard to fill all glycogen storage sites and then to maintain them. This study showed that muscles can store 800-900 grams of glycogen before becoming saturated. Extremely fit people can store 1 to 1.1 kilos of glycogen. The storage cites have to fill by at least 500 grams before fat synthesis can begin.


3. This study also showed that it is very difficult to maintain a saturated state of the muscles, since the glycogen is constantly being used, and presumably because the average person won’t eat sufficiently of carbs to ever get to saturation. Too, there is our fitness level, which determines how effectively we can fill and maintain our glycogen stores. 


4. Interestingly, the subjects in the study spontaneously burned more calories during the 9 days of over-feeding, too; so the scientists had to keep increasing calories to maintain an over-feeding state. On average, test subjects spontaneously burned an extra 840 calories per day, or 35% more calories, during the overfeeding period, presumably due to thermic effect (thermogenesis).Yes, you read that right: A high-carbohydrate diet causes the body to spontaneously burn more calories~up to 35% more calories than a high-fat or high-protein diet.


5. Only once the glycogen stores are filled to at least 500 gram capacity is the remaining glycogen able to be converted to fat. The body is capable of converting up to 500 grams of glycogen to fat per day. 


6. But de novo lipogenesis (glycogen to fat storage) doesn’t produce an equivalent amount of fat. That is 1 kg of glycogen doesn’t convert to 1 kg of fat. It converts to much less fat than that.  Since it takes about 25% of the glycogen calories to convert it to fat, only some 75% of glycogen excess makes it into fat.


7. Bottom line: Yes, glycogen can be converted to fat (de novo lipogenesis), but it takes a lot of excess for this to occur.


I would love to hear your responses to this study!  .........ana xoxo

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So, if one is 50 kilograms their storage capacity is 750g but once it's 2/3's full (500g) carbs start being converted into fat and at the same time also stored as glycogen, correct? If I'm reading this right, DR's recommendation of 10 grams of carbs per kilo body weight would be correct then. It would also make sense to eat the maximum of what he recommends because according to this study your body burns calories faster as carb consumption increases. 


Yes, the first two lines of your paragraph are correct.

As for the second half of the paragraph, that depends on how frequently you eat and how much you exercise. Note that it isn't 500g of carbohydrates in dietary intake, but 500g of glycogen storage capacity. So how much of the excess carbohydrates you will store as glycogen, and how quickly your body will store the excess carbohydrates as fat will depend how much physical activity you do on a daily basis. If you aren't depleting your glycogen reserves in exercise and sleep on a daily basis, you will store fat much more quickly if you are consuming a diet that provides 10g carbs per kg body fat.

Note that in the study above, the people were physically active. They were not sedentary. So their glycogen reserves were being depleted and replenished through activity and diet. The reserves may not have been always exhausted through activity. But they were depleted.

Take care

Adam x

Hey Adam

Could you tell me how much carbs can we store in the human body? I never swallowed that carbs can be store only into muscle and liver, is that true all cells can store carbs?

Carbohydrates are stored in the liver and muscles as glycogen. In the blood it's moving as glucose. Liver carbohydrates and blood sugar can supply carbohydrates to tissues throughout the body. Muscle carbohydrates can only be used by the muscles that it's stored in.

We can't use the Glucose stored in the legs as energy in the arms. That's why it's so important to carb up for days before and about an hour before any long duration exercise. Even in the gym or biking I'm eating small portions several times an hour. While everyone else complains of their legs burning I never get muscle burn by constantly refilling my tank. I'll systematically bonk before that happens. That's where I've burned out all liver glycogen and blood glucose and my body can't process food fast enough so my body runs mostly on its fat stores. At that point you slow to a crawl.

We were at the point where we did 30 century mountain bike rides in a month and didn't bonk. It's all about refueling at every possible moment without overdoing the re-fueling speed. 500-600 calories per hour while riding 12-15 hours a day, 7 days a week. Most people can only pull in 200-400 calories per hour while exercising. Total lean body mass is a big factor in how many calories you can re-fuel per hour.

Interesting stuff, Reed. Thanks. I never really thought about it, but you're right that glycogen can only be used by the muscle it's in! 

And good to know about how fast one's body can pull calories. I suppose that is why it's important to balance one's caloric output with fitness level. 

One other thought I had~an obvious one for sure, but something I never really gave much thought to~is how fast we can use up our glycogen stores. I mean just look at how often in a single day the body cries out for more (immediate) fuel. Wouldn't this surely be a sign to replenish glycogen stores? Obviously, the body isn't crying out to fill fat stores, after all.

I appreciate your insights.  .....ana xoxo 

Hey Ana

Well, the body cries out for more immediate food intake because the cells need carbohydrates and protein in regular supply. Glycogen gets used up during sleep to some degree (since we usually have a gap of several hours between our last meal of one day and the first of the next day, and when we are physically active. We will also dip into glycogen if we have big gaps between meals. So how quickly you dip into glycogen depends on how far apart you spread your meals (and how much you eat at those meals) as well as how physically active you are. Stress also affects it. Adrenaline promotes the breakdown of glycogen to glucose.

The body will only dip into glycogen during the daytime if there is insufficient food intake to meet our fuel needs. If we are physically inactive and eat plenty and consistently across the day, we won't use much glycogen during the day.

And remember the storage limit of glycogen is 15g/kg. How quickly you deplete glycogen depends on general calorie intakes, meal frequency and carbohydrate content of the diet. At 15g/kg, a 55kg female would have reserves of 3300 calories just from carbohydrates available as glycogen, if her glycogen reserves were saturated.

Glucose for energy is the main reason we demand food. And protein. But we do like to keep good glycogen reserves available, so that we have enough glycogen to support both physically activity, but especially sleep. That goes back to evolutionary adaptations - low glycogen reserves means low melatonin production and higher cortisol levels. This means increased likelihood you would be awake at night when the predators were out (most of our natural predators in the wild are nocturnal, which is partly why we evolved to be diurnal). If you are awake and can hear predators creeping around, or you are anticipating that, you will release pheromones with a signature that pertains to fear. Predators depend on this to find prey faster. So good glycogen reserves = increased chances of survival.

Take care

Adam x

That's very interesting! It sounds like you want to have stored glycogen. So, if you are trying to lose excess fat, how many calories do you suggest per day for a female who exercises 30-60 minutes 5 days a week (sometimes more)? 

Hey KGG,

Well, trying to estimate calories accurately based on gender and vague information about exercise (no idea what type of exercise or any other info) alone, is not really very easy. I mean calorie estimates are normally based on mathematical estimates of requirements at the best of times. And people don't all fit into those estimates, since they are based on averages, where some people actually need more, some people need less.

Calorie requirements will depend on protein intake, amino acid composition, age, height, weight (and goal weight), gender, stress levels, specific activity patterns including work and other factors. There are mathematical models that can be used to offer estimates. You don't need me to tell you those. Go on something like nutritiondata.com and you can get a rough estimate of your requirements. On a lfrv diet, it is hard to estimate accurately, since it is a low protein diet, and this changes the calorie requirements. And since everyones application of the lfrv diet looks different.

I think the general guidelines from this forum are a good starting point. Really, it is trial and error though. However many calories it takes for you to maintain a healthy weight (ie. not be losing healthy weight, especially muscle mass, and not be gaining unwanted body fat).

Like I say, I suggest using nutritiondata.com and tracking food intake on something like cronometer.com for a couple of weeks to work out food quantity based on these calorie estimates. Make sure you are meeting your amino acid requirements.

Take care

Adam x

Thanks, Adam. Let me digest this a bit more, then I'll get back to you.

Meanwhile, I'm just finishing reading a study that states that de novo lipogenesis is an adaptive state, that it wasn't originally a part of human functioning (i.e., when we lived in nature), but was adapted later on as we started over consuming carbohydrates. Have you heard/read of this?   


Well, everything is an adaptive state - that is what evolution is; A series of adaptations. There was no "originally part of human function". Evolution to homo sapiens sapiens was likely a gradual process through successive adaptations throughout generations. Long before humans were human, or even primates, we were capable of lipogenesis.

All mammals are capable of de novo lipogenesis. Because all mammals are subjected to the same inconsistencies with food supply in nature; Sometimes there would be plenty of food and sometimes there would be periods of insufficient food. Even acquatic mammals can do it. It is a very old capability.

As for overconsuming carbohydrates, that is something that was unlikely throughout history until very recently (except in rare groups over the last 10,000 since agricultural societies developed, where those at the top of the social hierarchy were able to eat large quantities).

Even now, our trouble with weight gain isn't that people overconsume carbohydrates. It is that they consume refined, processed, high GL carbohydrates and refined, processed dietary fats (oils) and high intakes of saturated animal fats and protein and  regular and excessive alcohol. We haven't had that many periods in history where there has been a consistent excess of calories to be able to suddenly evolve certain adatptations that would take hundreds of thousands of years minimum to develop. 

Can you send a link to the study so I can read what it says specifically?

Take care

Adam x

Hey Sandro

As Reed said, we store carbohydrates as glycogen (this is like our version of starch...it is just lots of sugar molecules linked together in a chain so that we can store more of them efficiently) in liver and muscles. And as I mentioned in my original post, the limit to glycogen storage capacity is 15g glycogen per kg bodyweight maximum.

Take care

Adam x

How is that possible to build muscle without doing any exercise? Is that true muscle mass or simple lean mass?



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