Carbs to Glycogen to Gucose to ATP. Fat to ketones.

[hank_marvin]

Hello all, I was just reading some old threads and stumbled on a quote by MartinM in the "Taurine while dieting" thread, which states that;

"The article is assuming that glycogen will have to be depleted to burn fat.........simply not the case"

Now I thought it was, I thought that after you deplete the carbs, the body starts to burn stored body fat and turns the fat into ketone's, which we use for fuel as opposed to carbs to glycogen to Glucose to ATP.

Where am I going wrong here?...

[NU_nutrition_TS]

From what I've read, I am given to understand that the human body is not quite so orderly as that! It uses various substrates [carbs/proteins/fats] for energy all the while - circumstances and availability will determine which one predominates at any one time. Needless to say, if you are constantly stoking yourself full of carbohydrates these will, of necessity, provide the majority of your energy requirements because the body cannot tolerate large quantities of glucose in the bloodstream at any one time. So, in this instance, more fat will be stored than will be utilised for energy.

[Ollie]

My understanding of the role glycogen plays is as follows.

Glucose is ingested in the form of carboydrates. Some of this is burned as fuel, whilst the remainder is stored as glycogen in the liver and the muscles.

The liver acts as a slow release supply of blood sugar, whilst the muscles hold glycogen for release during muscle contraction. Thus, when the 'right' amount of glycogen is ingested, there's no need for the body to store fat.

CONSTANT glycogen depletion is when problems arise: it can potentially alter thyroid functioning and will almost certainly have an effect on muscle tissue.

To amplify fat release in the short-term, carbohydrate manipulation is necessary. This can cause glucagon to be released, which will cause the release of fatty acids into the bloodstream for use as fuel. That's why you'll see low intensity cardio prescribed in a glycogen depleted state. Provided you're not CONSTANTLY glycogen depleted, you will burn more fat, all else equal.

Hopefully that clears things up a bit. As I've said, that's my understanding of it...someone please correct me if I'm wrong

[NU_nutrition_TS]

I would only disagree with one thing, Ollie...Carbohydrates are converted to blood glucose - some of which is burned for energy and some is converted to and stored as glycogen in the liver and muscles...the remainder is converted into triglycerides and stored as body fat. It is estimated that as little as 100g of carbs a day is all that is required to keep these glycogen stores topped up. If you are consuming in excess of that [and most people here seemed to be consuming four times that much!] then a sizeable portion of that must be converted to fat! So as you say, unless you manipulate your carb intake, i.e., consume less, you will not shift much in the way of bodyfat.

[hank_marvin]

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It is estimated that as little as 100g of carbs a day is all that is required to keep these glycogen stores topped up.

I read that the average person stored 200 grams of carbs as glycogen in their muscles and another 30 grams in the liver which is used primarily to fuel the brain.

[Ollie]

Nu - I realise that, hence my saying when the 'right' amount of glucose is consumed.

Whatever the amount is, I think Nu has a point in that the western diet contains far more carbohydrate than we need

[Duncan]

Yeah- As I read more on this subject I'm starting to look at carbohydrate as a bit pointless after the necessary amount when compared to fats, because where carbs seem to be useful exclusevely as an energy source, fats are a source of energy and have a structural importance in the body. In fact, it's been mentioned several times that it would be possible to survive with the exclusion of dietary carbohydrate, while it would probably be a stupid and unhealthy thing to do.... In the context of its over-use in the western diet, carbohydrate is starting to look like a bit of a pointless nutrient, really!

[NU_nutrition_TS]

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I read that the average person stored 200 grams of carbs as glycogen in their muscles and another 30 grams in the liver which is used primarily to fuel the brain.

This is assuming that glycogen stores are fully depleted. Some research I have read in a recent edition of The New Scientist says that this is not the case...another evolutionary safeguard...we never completely run down our glycogen stores. Also, the brain is the only organ that absolutely requires glucose to function but it has been established that it can cope quite nicely if 25% of its energy comes from glucose and the remainder from ketone bodies [from fat metabolism]. This is the essence of the efficacy of long-term ketogenic diets in the treatment of epilepsy and brain tumours.

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Nu - I realise that, hence my saying when the 'right' amount of glucose is consumed.

Whatever the amount is, I think Nu has a point in that the western diet contains far more carbohydrate than we need

Agreed

[Tom]

de novo lipogensis, the conversion of carbohydrates (in any form) to fat because when glycogen stores are fuel (and for most people they almost always are) theres no where else for the excess carbs to go so they are converted to fat.

[MartinM]

Was worried there that you had found something I had said that was wrong............phew

The body will most certainly burn a lot of fat even with full glycogen stores. In general it is very hard to get the body to burn what YOU want it to burn, especially in regards to performance nutrition.

Exercise intensity mostly determines substrate use and the degree to which this can be done is affected by numerous other factors.

The body can store more than 200g of Glycogen in the muscle, its more like 300g but varies on muscle mass......and i'm sure the liver glycogen stores are in excess of 90-100g

The type daily activity you partake in dictates exactly how useful carbs are........certainly in the case of most athletes you'd get laughed at if you tried to prescribe a low carb/high fat diet..........and rightly so