T Nation

What Happens to Carbs when Glycogen Stores are Full?


when muscle glycogen stores are ‘full’ at say 500g and 600-700g of carbs are being eaten daily
what happens to the excess carbs that are eaten are they stored as body fat??
many sources say this is the ‘fate’ of excess carbs when glycogen stores are ‘maxed out’

According to ‘lyle mcdonalds’ in depth articles on his site he states that carbs are rarely if ever stored as fat or converted to fat through ‘de novo lipogenesis’

I ask as being a bodybuilder I want to eat a high carb diet and keep glycogen stores full for gains in strength and muscle mass
but there seems to be two different opinions/thoughts for the true fate of excess carbs when glycogen stores are full

this seems to be a controversial question that has two arguments/opinions

I ask you Christian as I hear you are a clever and helpful guy

thanks for the help/explanation


Calories consumed in excess of metabolic requirements, whether they are in the form of carbs, fat or protein, will result in increased fat stores.

If you re-read McDonald’s article, he discusses how excess carb intake results in dietary fats being incorporated into fat cells. This fact leads some people to conclude erroneously that they can consume excess (ie, above metabolic requirements) carbs, and so long as they consume no dietary fats, they can’t gain adipose tissue. Two problems with this strategy:

  1. It’s virtually impossible to consume a truly fat-free diet.

  2. In the absence of dietary fats, the body will deal with excess carb and/or protein calories via de novo lipogenesis. (Note that it’s not the case that humans cannot engage in de novo lipogenesis; rather, it’s that this process is suppressed by the presence of dietary fats, and thus doesn’t occur in the context of a normal diet.)

tl;dr If you overeat (carbs or otherwise), you’ll get fat.


yes I read the articles and understood them
and I know that excess calories will cause a gain in bodymass (muscle tissue/fat) depending on several indiividual factors
have been bb many years

what I am trying to find out from CHRISTIANS input
specifically for the scenario of my question
what is the true fate of excess/surplus carbs that are being eaten when glycogen stores are ‘maxed’ out

are they stored as body fat
as most sources do say, such as ‘chris aceto’ in his book and articles

or are carbs rarely ever stored as fat as lyle mcDonald says for his various reasons/explanations

hopefully Christian will contribute here

thanks for reading here


forget getting chubby, thats type II Diabetes on a plate right there


Well first if you want to increase your chances of me answering your question don’t mention Lyle McDonald :wink: I get along with absolutely everybody in the strength training community but for some reason Lyle hates me and has resorted to personal attacks in the past (even though we used to be “friends”). So when I read his name I normally stop reading.

He is a actually a very smart guy and does a lot of research. But sometimes he is more of a theorist.

What is the possible fate of ingested nutrients?

  1. Stored as energy (glycogen or fat)
  2. Used to build and repair structures (muscle, organs)
  3. Used to build hormones
  4. Burn off a fuel or heat
  5. Pissed out

Carbs can obviously be stored as glycogen either in the muscles or liver. And while Lyle argue against it (he likes to argue against everything) carbs CAN be stored as fat. They can also be burned off to produce energy or heat.

But carbs cannot be used to build muscle or organs… well to be fair “energy” is needed to fuel the repair processes so carbs can be useful but they are not building material.

And only protein (peptide hormones like GH, insulin, IGF-1) and fats, or more precisely cholesterol (steroid hormones like testosterone, estrogen, cortisol, DHEA, etc.) are used th -build hormones.

So basically when it comes to carbs they are either:

  1. Stored as energy (glycogen or fat)
  2. Used for energy (by the brain, muscles or organs)
  3. Burned off as heat
  4. Pissed out

Let’s assume that your glycogen stores are full. Then the fate of carbs is either…

  1. Stored as fat
  2. Used for energy
  3. Burned off as heat
  4. Pissed out

Now unless you suddenly have a sharp increase in caloric expenditure from carbs (which means a VERY important increase in high intensity exercise) there is only so much energy you use per day. To paraphrase Dr.Serrano (who I trust a lot more than Lyle since he has tons of experience helping patients ranging from average Joes up to Mr.Olympia competitors and pro athletes) on top of having an amazing amount of knowledge; doing a workout like 10 sets of 10 reps on squats will “burn” around 250 calories (the caloric estimation on the threadmill are bullshit to quote him). Even if that was 100% from carbs (which is not the case, it’s about 60-70%) it would account for about 60g of carbs… so let’s say that a high volume workout can burn around 100g of carbs; since you aren’t burning a lot of carbs during the rest of the day (unless you work a physical labor job) it is unlikely that you will burn all of the excess carbs.

You can also use carbs to produce heat. Now, if you work outside in Canada, in the winter, it might make you burn off some additional carbs due to the need to elevate body temperature. But if you work inside or in a hot climate the only spikes in heat production will be for a short period immediately after a meal. Is that enough to prevent the excess carbs to be stored as fat? Highly improbable.

As for pissing it out, it happens. There is actually a new drug to prevent diabetes that basically makes your piss a large amount of the sugar you eat. But in a normal adult it’s only a few grams per day. A high amount of daily glucose in the urine might be a sign of a kidney issue. But I could see how someone with a very high carbs intake could be healthy and pee 50g or so of glucose per day. But it begs the question “why eat those extra carbs if you are going to pee them out?” … is it just to satisfy your carbs cravings?

Now if you add up all these elements it might mean that you wont store all the extra carbs as fat. But if you overconsume carbs when your muscle glycogen stores are full you will still store a good proportion of it as fat.

And also remember something… let’s say that your muscles have a storage capacity of 500-600g. Well that doesn’t mean that you can/should eat 500-600g of carbs per day since you are unlikely to use up all the stored glycogen in a day, especially if you are on a muscle-building phase consuming calories at or above maintenance.

Let’s say that you use 100g of carbs during your workout (which is likely an overestimation), you are pissing out 50g per day (again, unlikely but I’m going with the highest numbers), your brain uses around 150g per day and if you are sedentary you will likely use around 100-150g to fuel other metabolic processes.

So that comes up to AT THE MOST 400g per day BUT MOST LIKELY AROUND 300 or even 250. The carbs above that will be stored as fat. It might not be enormous, but it can add up pretty quickly.

No to mention that consuming carbs throughout the day will spike insulin throughout the day too (if you eat 20g or more in one sitting it is likely to spike it). The problem is that insulin greatly inhibits fat mobilization. In other words as long as insulin is elevated you are less efficient at mobilizing fat to use for fuel. So if you eat carbs all day long you might not store all of them as fat (maybe not even a large amount either) BUT the fact that you are greatly reducing fat mobilization lead to the same result: more fat cell growth. It’s like a bank account: if you only deposit a small amount each day but you don’t take anything out, the account will still grow.

“Yeah but many bodybuilders eat rice 4-5 times a day”…sure, but taking thyroid hormones, growth hormone and clenbuterol (some even use DNP… with DNP the more carbs you eat the more effective it is) changes everything when it comes to carbs and fat loss.

My opinion is that carbs are not evil and muscle growth does occur faster when there are carbs in the diet… BUT you don’t need a huge amount to get the benefits and you CAN get fat from eating too many carbs (even if it were strictly due to an indirect effect, which it isn’t, the result is still the same).

Again if someone is not natural it changes many things. I am friends with a two guys, a pro boybuilder and a strongman and they eats TONS of carbs. But they also use steroids, growth hormone and peptides (bodybuilder uses fat loss drugs). They don’t get TOO fat, but they don’t stay as lean either.

Hope this helps.


That’s the thing that most people don’t consider: the health effects. They don’t care about them. And I understand because I was once like that. But it does catch up to you and once you have some of these problems you can’t go back.


By this theory if you eat ONLY CARBS but ingest 7000 calories per day you wouldn’t gain any fat then? So if you eat 7000 calories of only candy (which is basically only sugar) fat gain would be impossible since you are not consuming any other nutrients and carbs can’t be stored as carbs… does that really make sense?

I always use the “test of extremes” to see if something is logical or not. If carbs are rarely, if ever stored as fat then eating only candy would actually get you leaner since you shouldn’t be able to store carbs as fat, you aren’t consuming any fat or protein and you are burning energy daily.


Unless you are training 6-8 hours a day you don’t need as much carbs as you think you do to keep muscle glycogen stores full.




By fat, you mean bloated right?
Because fats bloat, bloat fats aren’t the same. The latter is fat32.

Really appreciate your reply.


It’s a really good read.


Just to clarify–in healthy individuals, essentially 100% of filtered glucose is reclaimed by the kidneys. The upper limit of normal for urine glucose is ~0.8 millimoles/L, which over the course of a day would total to an infinitesimal amount–under a gram.

Individuals ‘spill glucose’ (fail to reclaim it and thus allow it to enter their urine) under only four circumstances of which I’m aware:

  1. they’re taking certain diabetes medications, as mentioned;
  2. they have renal disease;
  3. their blood glucose level is so high that the kidneys simply can’t keep up. This doesn’t happen until blood glucose levels exceed 200 mg/dL–in which case, by definition, the individual has diabetes; or
  4. if they’re pregnant (some pregnant women spill glucose despite normal renal and metabolic status).


Thanks CT that was a cool answer

apologies for quoting ***** and disappointing you

can I try to recap with you and keep it fairly simple for me I do not have a overly scientific mind and can only absorb straight forward/simplified information
I have slight learning disabilities in honesty which is a bit embarrassing
but I am not simple :slight_smile:

both you and ***** seem to have different answers/opinions for my question
I think ***** says that excess carbs are only stored as body fat when glycogen stores are 'full’
but calories also have to be eaten in excess for this to occur I am not certain on this

which seems to go against what I think you are saying along with most other bodybuilding/nutrition sources…
is that any excess carbs eaten when glycogen stores are already 'totally full’
regardless or not if they are full at 400g and 500g are being eaten or they are ‘full’ at 300g and 400g are being eaten
they are indeed actually stored as body fat if they are not required for glycogen storage or for energy

can they/are they stored when eaten in excess regardless of current calorie consumption, as a simple case of because they have ‘nowhere’ else to go when glycogen is full

until I read ***** articles fairly recently
I myself over the many years did always believe that when carbs are eaten in excess when glycogen stores are full are stored as body fat
mainly to quote ‘chris acetos’ work who I hope is not a problem to mention

to quote 'chris aceto’
who I gather is highly respected and experienced in the industry
in his book 'championship bodybuilding’
he says-
‘once muscles are fully loaded with glycogen, all extra or excessive carbs
will be stored as body fat’

also in his following article on rxmuscle
’chris aceto explains nutrition myths that wont go away!'
it says-
Myth: Carbohydrates Can Not Be Directly Stored as Body Fat

Truth: Don’t laugh. That’s been the idea held by many astute physiologists over the years.
The belief has been that excess carbohydrates are not directly stored as body fat but must first be channeled through more complicated metabolic pathways in order to make you fatter. Well, the gig is up.
Carbohydrates can make you fat in three different ways. Yes, that’s right THREE!
First, all carbohydrates will be stored as body fat when muscles are already full of glycogen. It follows that a continuous high carb diet will lead to fat gains.
Second, the insulin burst associated with eating carbs can trigger the fat storing machinery in the body.
Third, and here’s the surprise, carbohydrates can directly increase fat storage. Known as “de novo lipogenesis” or the “conversion of carbohydrates into fat”,

so is chris correct in what the above is saying to me it makes sense
and do you agree with him CT?
are carbs actually stored as body fat when eaten in excess and glycogen is already ‘maxed out’ regardless of the calorie content of the diet?

however ***** says that ‘dnl’ rarely ever occurs in humans and only kicks in and stores carbs as fat when dietary fat intake is below 10% to stop the body
being tricked into never gaining fat

which is not what chris seems to say in his work above, and he makes no mention that calories must also be in excess at the same time glycogen stores are full
for the excess carbs to be stored as body fat
I like chris’s work as it is wrote in a simplified but informative interesting way

can you help answer/clear this up for me as to what happens to any extra carbs eaten when glycogen stores are already full to ensure I have the correct answer/knowledge

apologies for being so long winded and asking

I did hear that you were the helpful smart guy around here to go to on the forum
so wanted to seek your answer directly as there is a lot of bogus information and so called experts on the forums
and to see if you thought … was correct or agreed more with Chris aceto

I hope you can find the time to answer my above individual questions in a simplified way
many thanks


sorry CT I forgot to add earlier

if glycogen stores remain consistently ‘full’ every single day from a high carb diet
and excess carbs are still being eaten each day on top of the amount of carbs required to keep glycogen stores 'full’
THEN are the excess carbs stored as body fat ?

thanks CT


Most of it yes, some will be burned off as heat or energy through fidgeting or every involuntary movements


They have done some studies on fat accumulation on overfeeding carbs vs fats.

The study below found fats store easier as fat than carbs.

Carbohydrate overfeeding produced progressive increases in carbohydrate oxidation and total energy expenditure resulting in 75-85% of excess energy being stored. Alternatively, fat overfeeding had minimal effects on fat oxidation and total energy expenditure, leading to storage of 90-95% of excess energy. Excess dietary fat leads to greater fat accumulation than does excess dietary carbohydrate, and the difference was greatest early in the overfeeding period.

The two studies below found no differences:

There was no significant difference in fat balance during controlled overfeeding with fat, fructose, glucose, or sucrose.

Thus, fat storage during overfeeding of isoenergetic amounts of diets rich in carbohydrate or in fat was not significantly different, and carbohydrates seemed to be converted to fat by both hepatic and extrahepatic lipogenesis.


thanks CT

did you also read my LONG post above

can I just recap/summarise with you

so you agree with ‘chris aceto’ when he says all excess carbs are stored as fat when glycogen stores are already full?
and is this the case CT even if calorie intake does not exceed maintenance requirements?
so long as glycogen stores remain ‘full’ then the extra carbs are stored as fat regardless of calorie intake as there is no other place for them to go?
or must calories also be eaten in excess for the carbs to be stored?

seems like Mr…has a different opinion/answer
but I know you and Mr aceto are smart guys

thank you sir I appreciate your answers here


thank you for your contribution Marcus

I read the studies but are they saying/implying or related to the answer
that excess carbs eaten when glycogen stores are already full are stored as body fat?


In a fat lose process or contest prep when you do a heavy load once a week, keeping the rest of the week in a low/moderate (only periworkout) amount, such production of heat plus next day training would improve the fat lose process? I’m talking without using fatburners or another agents. i’m talking in practical or biochemical terms.


Not 100%

If you consume a caloric deficit but glycogen stores are full you are likely to use the carbs for energy BUT that should also decrease the use of stores fat for fuel. But a significant part of it WILL be stored as fat.

BUT when you are consuming a caloric deficit it is fairly hard to maintain glycogen stores that are completely full IMHO.

Foe what it’s worth, and it pains me to say it, by McDonald is much smarter than I am about dieting. I’m more of a training guy than diet guy. HOWEVER lots of coaches with a much better track record and experience than Lyle think like Aceto… research is important but real life results are important too, maybe more so.