fasted or not?

[G-dub]

For the sake of clarification, aren't we talking about "fasted" being between 12-16 hours between meals? Not the sort that Ghandi would have attempted.

[jackarabit]

I've always thought the LSD/sourcing fat theory that dominated weight loss-driven exercise programs may have contaminated the much older idea of the fast. Fasting is a universal norm if all it means is not raiding the fridge between 10PM and 6AM. Maybe the gut needs a rest.

Not breaking fast for breakfast is something I've done to rub the fat access/weight loss rabbit's foot. HAHA! Maybe that's why I can touch my toes, ya think? Most of our kinky ideas about weight loss are obsessively talismanic. "Worth a try, might help."--right?

Is blood glycogen at its lowest upon waking?

[Tim K.]

The second you take in glucose (or fructose/sucrose) you're effectively shunting fat utilization for fuel.

I apparently dont know how to communicate without sounding mad, stressed or offending someone so Im just going to come out and say it. Im not mad, stressed or trying to offend anyone.

According to everything I have read, several LC ultra marathoners consume gels during their events but at about 1/3 the rate of the non fat adapted. They continue to use fat as required, the glucose that is consumed simply "tops up the tank" as fat utilization has a cap some where around 60-70% VO2max. This is the point I was trying to make in the Performance Diet thread that it seemed some did not want to hear. It is my understanding that as long as you do not over consume glucose to the point you begin to convert it to fat, you will retain your access to fat. Once you have consumed enough sugar to cause your body to begin to convert it to fat and store it, you locked out for a "while"

[Cyclingman1]

It really shouldn't surprise me at this point since I've been a member of these forums for years, but the amount of BS that gets posted by people is just absurd.

Man, you took the words right out my mouth. Yes, there have been tons of elite marathoners over the years who have hit the proverbial wall. Glycogen stores can vary by day, but marathoners have about 1500 calories from glycogen to use in a marathon. Assuming about 100 cals a mile, a marathoner will need about 2600 calories. Of course, exercise uses both fats and glycogen. But it doesn't take a genius to see that preserving enough carbs to finish is a balancing act. You get it wrong, you hit the wall. Also, it is calories per mile, not calories per hour. A 4.5 hr marathoner does not use twice the calories of a 2:15 marathoner. BTW, it is a glycogen depleted state that promotes fat utilization. Simply not eating for 12 hrs does not produce that.

[hjs]

There seems to be a good bit of confusion about when one eats and muscle glycogen stores. Not eating during the night and early morning does not deplete muscle glycogen. You may think you are burning mostly fats, but not so. Depletion of glycogen occurs after a couple of hard hours of exercise or several days. Do that, restrict carbs, and then see what you think about rowing 60 mins on a no carb diet, fasting, etc. The fact is that one cannot go fast without carbs. Fat burning is for slow going. Why do world class marathoners tend to hit the wall near the end. It's because their glycogen stores are nearly exhausted and their bodies cannot support 5 min miles on fat stores. They have to slow way down or hit the pavement. The same applies to cycling although the stomach is more accepting of food while on a bike, which also applies to rowing. One can stave off depletion to some extent on a bike.

Glycogen in muscle only gets used on that muscle, nowhere else, only liver glycogen can enter the bloodstream.

If you have eaten normally, food is not needed at all in the morning, that was the original question.

You can go plenty fast without carbs, you can not go anaerobic well without enough enough glycogen, short fast or long easy is ok. Inbetween not. I have never seen a top athlete in any sport eating low carb. Every runner, cycler, swimmer eats carbs.

We can eat if we go slow enough to have blood left for the stomach. Tough efforts make eating difficult. In cycling those guys eat almost all day long, but most of racing is done relative very easy. Riding in the wheels in a cruising peloton gives lots of drag.

[ArmandoChavezUNC]

Is blood glycogen at its lowest upon waking?

Blood glucose - glycogen is how glucose is stored in the liver and muscles, not in the blood.

[ArmandoChavezUNC]

According to everything I have read, several LC ultra marathoners consume gels during their events but at about 1/3 the rate of the non fat adapted. They continue to use fat as required, the glucose that is consumed simply "tops up the tank" as fat utilization has a cap some where around 60-70% VO2max. This is the point I was trying to make in the Performance Diet thread that it seemed some did not want to hear. It is my understanding that as long as you do not over consume glucose to the point you begin to convert it to fat, you will retain your access to fat. Once you have consumed enough sugar to cause your body to begin to convert it to fat and store it, you locked out for a "while"

Your body is always using fats and carbohydrates for energy. In fact, it even uses protein to a very small extent. Perhaps shunt wasn't the best word. If you look at graphs of fuel usage at different exercise intensities, you'll find that for exercise below 65% of VO2max fats are the predominant fuel. This doesn't mean that you aren't using carbohydrates, it just menas you are using fats as the primary fuel source. Once you get past that 65% of VO2max area, you start using carbohydrates more and more and using fats less and less.

Fasted training promotes even more usage of fats at low exercise intensities, but the second you increase the concentration of glucose in the blood you immediately drop down the usage of fat. Think of fats and carbs as competing fuels. In fact, if you take a deep dive into the biochemistry, you'll see they have a very close feedback mechanism. You'll still be primarily using fats, but not to the extent you were when you were truly fasted.

I think one of the hang ups is that no one really has a set definition for what fasted really means. Working out 3 hours after a meal certainly isn't fasted. I would say anything over about 8 hours is approaching fasted territory. Certainly working out in the morning before eating breakfast would be considered fasted training.

[ArmandoChavezUNC]

Also, it is calories per mile, not calories per hour. A 4.5 hr marathoner does not use twice the calories of a 2:15 marathoner.

Calories are a function of exercise intensity and body mass. A 4.5 hr marathoner could very well use twice the calories of a 2:15 marathoner, especially if they are very heavy. Not likely, but ignoring body mass ignores a huge part of the equation.

Glycogen stores can vary by day, but marathoners have about 1500 calories from glycogen to use in a marathon. Assuming about 100 cals a mile, a marathoner will need about 2600 calories. Of course, exercise uses both fats and glycogen.

So you're under the impression that an elite marathoner only has 375 g of glycogen stores? That's way off.

[skiffrace]

Our bodies use a mix fat + carbs to fuel its efforts.
Carbs (glycogen) is the preferred source for hard efforts, but its supplies are limited.
As noted above, on average we have ~1500 Kcal stored as glycogen in the liver and muscles, which is good for about 1.5 hrs of hard effort.
So, yes, you can perform well while fasted, where "fasted" = "not eating in the morning before workout".
After the 1500 Kcal of glycogen are depleted, here is what happens next:
A. Carbohydrates are ingested, quickly converted to glycogen, hard effort is maintained.
B. Carbohydrates are not ingested. The athlete must now rely on fat as energy source ... the level of effort drops off substantially.
Using the marathon example, the athlete slows down dramatically, or switches to walking.
Everybody has enough fat to walk (but not run), or ride bicycle slowly (but not fast) on empty stomach for hours and hours....

[gregsmith01748]

At the risk of wading into a topic that is somewhat polarized. My opinion about fasted training has been influenced by an article that I read recently. The obverall topic of the article was the factors that maximize the level of fat metabolism during exercise. It was a review article so it drew on a number of other studies and summarized the effect on fat metabolism based on exercise intensity, fitness, gender, and how recently carbohydrates were consumed prior to the session.

I was interested in this because I am a big believer in polarized training, and when I do low intensity sessions, my primary objective is to maximize fat respiration to raise the intensity at which I need to rely upon glycogen respiration.

The findings regarding fasted state were surprising to me. I had not seen such a clear conclusion of the effect on maximal fat metabolism elsewhere.


Basically, training in a fasted state increases the level of fat metabolism by more than 20%, and increases the exercise intensity you can achieve before the crossover to CHO metabolism takes place. In other words, your endurance training can be more effective if you do low intensity training in a fasted state.

If you are doing a high intensity session, then making sure that you have sufficient glycogen to feed you muscles in the session is a high priority, so doing sprint sessions or time trials, even long time Trials like Marathons or half marathons, in a fasted state counter productive and can lead to bonking.

Here is a link a summary of the whole article: https://quantifiedrowing.wordpress.com/ ... -and-diet/

[ArmandoChavezUNC]

Everybody has enough fat to walk (but not run), or ride bicycle slowly (but not fast) on empty stomach for hours and hours....

More like weeks. The amount of calories in the fat stores of an average individual are in the many tens of thousands.

After the 1500 Kcal of glycogen are depleted, here is what happens next:
A. Carbohydrates are ingested, quickly converted to glycogen, hard effort is maintained.

Why in the world would your body do something like that? Carbohydrates are already in the form they need to be to be utilized as fuel. It would be counterproductive to convert them to glycogen then back into glucose. Your body only coverts carbohydrates to glycogen when your blood glucose levels are at baseline or above, not when you're hypoglycemic. Those carbohydrates are immediately consumed.

[Tim K.]

Your body is always using fats and carbohydrates for energy. In fact, it even uses protein to a very small extent. Perhaps shunt wasn't the best word.

I guess everything is always situation dependent and as usual Im voicing an understanding without enough qualifiers.

LC ultra marathoner, glycogen tank is not full, pulling fuel from both sources, majority (depending on load) from fat balance from glycogen stores and external sources
High carb marathoner, glycogen tank is not full, pulling fuel from both sources, majority from glycogen stores and external sources, balance from fat.

If the LC marathoner over consumes carbs during the race to the extent the liver starts to produce lipids, it is my understanding he is locked out of lipid metabolism for a period of time as you are either in lipid metabolism or lipid storage "mode" The same would hold true for the High carb runner but consequenses are less as lipids are a much lower portion of the energy equation. This is a hypothetical as it is highly unlikely an athlete would be in the position to over consume during an event

After the event, it is my understanding the same would hold true. If you consume excess sugar and your liver is producing fat, you are putting fat into adipose tissue, your fat metabolism shuts down (a one way process, its either going in or coming out).

Ben Greenfield states it isnt even dependent on lipogenesis. He states that as soon as insulin response is sufficient lipid metabolism is halted.

https://greenfieldfitnesssystems.com/ar ... s-you-fat/ 5th paragraph

"Two actions occur when the insulin levels are spiked. First, the body’s fat burning process is shut down so that the sugar that has just been ingested can be immediately used for energy. Then, insulin takes all that sugar and puts it into your muscles"

Does this make sense?

[Cyclingman1]

So you're under the impression that an elite marathoner only has 375 g of glycogen stores? That's way off.

Actually, Mr. Antagonistic, it is right on the money. Glycogen stores are proportional to body size. Some persons may go up to ~500g [2000 cal]. But 1500 calories for elite marathoners is very close.

[MarkEg]

Thanks for all the replies -- seems like a contentious subject. Personally I'm going to stick with eating breakfast and then exercising 3-4 hours afterwards, which, from experience, is when I feel best. If there are fat-burning benefits to be gained from fasted workouts, I might just be willing to forego them based on what I'm reading.

[hjs]

Everybody has enough fat to walk (but not run), or ride bicycle slowly (but not fast) on empty stomach for hours and hours....

More like weeks. The amount of calories in the fat stores of an average individual are in the many tens of thousands.

After the 1500 Kcal of glycogen are depleted, here is what happens next:
A. Carbohydrates are ingested, quickly converted to glycogen, hard effort is maintained.

Why in the world would your body do something like that? Carbohydrates are already in the form they need to be to be utilized as fuel. It would be counterproductive to convert them to glycogen then back into glucose. Your body only coverts carbohydrates to glycogen when your blood glucose levels are at baseline or above, not when you're hypoglycemic. Those carbohydrates are immediately consumed.

Indeed, thats why cyclists keep on eating more or less not stop in the form of simple sugars. This directly is used as fuel, certainly not stored as glycogen.