Burning fat through exercise or ketosis...

[fodus8]

Maybe someone can post a link or an answer to this question which I was thinking about the other day. Sorry if this has already been asked.

I was at the gym thinking about how exercise burns fat (I actually don't really know exactly how it works - exactly.)

Question is: Is the body's fat burning process the same in exercise as it is in ketosis?

It seems to me like the body would have to go through the same steps to burn fat whether it's through exercise or ketosis (whatever exactly that process is.)

The way I understand it is when a person exercises, stores of glucose and fat are being burned for fuel.

If exercise and ketosis are handled the same, wouldn't that automatically make the Atkins diet good for you?

Any thoughts?

[mem2]

I hope you get a lot of responses to this. Its a good question. Recently I bought a scale that measures body weight and body fat. I have been weighing every morning and my weight is going down, but the fat percentage was going up until I started being more active. I still have a long way to go. I don't want to stay at 30% body fat.

[Faithnj]

I can't wait to see some of the answers you get from the truly informed people around here. But until then, I'l share my personal experiences:

I'm a vegetarian low carber, and when I first went low carb, I noticed a lot of people complaining that they couldn't get into ketosis. Hmmmm. If it should be difficult for anybody, it should be difficult for a veggie, right? Anyway...

I also did a lot of exercise videos. Sometime really tough ones, too. And you know what-- [B]I NEVER[B] had any trouble getting into ketosis. (Oh happy, happy, joy, joy! Faith is dancing.) I lost 21 lbs with that combination last summer, too. In fact, I think if you exercise, you can probably eat a few more carbs than the next guy. (But YMMV.)

So, I may not have any scientific answers to your question. But I do have my own personal experience that suggest low carbing and exercise make a winning combination.

Faith

[Quinadal]

I'd ignore anything fodus posts. Every one of their other posts has been anti LC.

[mps]

I'll reply because it seems like the question is interesting to some...
The short answer is no, they are not the same.
Ketosis occurs when there is incomplete oxidation of fatty acids. As long as enough carbohydrate is available, fats will be burned completely.

Excerise uses energy at a higher rate than when you are just sitting around but it does not produces energy in a fundamentaly different way.

If you are already in a fat-burning state, you will most likely burn a higher percentage of fat during the workout. But it depends somewhat on the type of work also. Anaerobic, high intensity will use ATP/CP pathways first, then glycogen, then fat.
Just sitting around you're burning mostly fat. Low intesity your buring mostly fat.
This does not mean that low intensity is better for buring fat however. You may burn more calories during high intensity training, both during and after the activity, and therefore end up with more of a calorie deficit and thus more fat buring over the course of the day.

Ketosis is mostly a function of lack of carbohydrate not induced by training. The exception is that if you do a workout that depletes glycogen you will then have less carbohydrate in your body and may go into ketosis faster than if you had not worked out.

[Faithnj]

Well, now THAT was some interesting information!
Thanks for you reply!

And your last paragraph explains why as a veggie during induction, I was always able to get into ketosis if I exercised. (For veggies, going to 20 grams of carbs a day is a LOT harder. I can get down to 30-40 grams of carbs okay though. But I do wonder-- if I could get into ketosis as a veggie, why do some meat eaters have a hard time going there? It would seem that doing induction would be easier for them, considering the wider range of foods they have available to them??? Oh well. That's probably another subject.)

Faith

[Built]

WOW!

As always mps, an excellent and informative post.

:)

[fodus8]

I'm pretty certain I did post a few negative comments on this board over a YEAR ago. I've been on the Atkins/S. Beach for about 7 months and I'm feeling great! Please don't hold a grudge against someone who didn't really understand the complexity of the diet and asked a few questions.

I think my question of exercise and ketosis is very difficult to explain.

1. When I exercise I'm burning different types of fuel. Stored glucose and FAT are two such fuels (I think).

2. When I'm following Atkins my body is also burning FAT for fuel. Ketosis.

OK: My question is: Does the body break down, process, etc, FAT fuel differently in these two cases or is the FAT fuel all the same to the body?

Does the body say: "Hey, we've got some FAT for fuel, a FAT is a FAT, is a FAT. Let's get to work." Or does it say, "Hey this is exercise FAT and it's way different than Ketosis FAT."

Does that make sense?

[fatburner]

I'll reply because it seems like the question is interesting to some...
The short answer is no, they are not the same.
Ketosis occurs when there is incomplete oxidation of fatty acids. As long as enough carbohydrate is available, fats will be burned completely.

Excerise uses energy at a higher rate than when you are just sitting around but it does not produces energy in a fundamentaly different way.

If you are already in a fat-burning state, you will most likely burn a higher percentage of fat during the workout. But it depends somewhat on the type of work also. Anaerobic, high intensity will use ATP/CP pathways first, then glycogen, then fat.
Just sitting around you're burning mostly fat. Low intesity your buring mostly fat.
This does not mean that low intensity is better for buring fat however. You may burn more calories during high intensity training, both during and after the activity, and therefore end up with more of a calorie deficit and thus more fat buring over the course of the day.

Ketosis is mostly a function of lack of carbohydrate not induced by training. The exception is that if you do a workout that depletes glycogen you will then have less carbohydrate in your body and may go into ketosis faster than if you had not worked out.

Now I'm confused again. I posted a question on a recent 'metabolic advantage of low carb' thread about whether there was a difference between ketosis (exercise or dietarily induced) and burning FFA's in your mitochondria without a ketone in sight. Somebody replied with quotes from some biochem texts which stated quite clearly that FFA metabolism directly in your mitochondria is a quite distinct metabolic energy pathway to ketosis. They both end up using acetyl CoA in cells, but get there via different metabolic pathways. Ketosis is very inefficient, which makes it such a star turn for weightloss, whereas free fatty acid burning in mitochondria is a very clean burn. Particularly because direct FFA metabolism in cells does not produce lactate as a by product as glycogen does. Both metabolize fat of course, just differently. So can you be burning just fat for energy, no glycogen, and not be in ketosis at all, particularly when you low carb long term? MPS and Built, HELP!

[mps]

I think the confusion here is about ketosis and fat burning. If you are in ketosis then you are burning fat incompletely and producing ketones. If your not in ketosis that does not mean that you are not burning fat. It's all the same fat... just used completely in the Krebs cycle (fat burning/ATP/energy producing pathway) or not. Your workout will have no effect on this. It will just speed up whichever fat burning process you are in.

Your question is difficult to answer without me knowing what you know about the causes of ketosis and fat metabolism. But anyway, as far as fat burning... it's all the same fat and the same process, workout or not. The workout will just make it happen at a faster rate because you need the energy at that time.

I hope this helps...?

[fodus8]

I found some good info on Exercise Intensity and Fuel use, but alas, this is not what my orginal question was about.

Exercise Intensity and Fuel Use
The relative contributions of fat and carbohydrate to energy vary with exercise intensity. Low-intensity activities such as walking strongly stimulate lipolysis from peripheral adipocytes, while intramuscular triglycerides contribute little or nothing to total energy expenditure (1). The rate of carbohydrate use is also low: carbohydrate needs are met predominantly by circulating blood glucose, with little or no muscle glycogen breakdown (figure 1: not shown). The rate of appearance of fatty acids into the plasma peaks during low-intensity exercise (25% to 30% of VO2 max) and then declines as exercise intensity increases.

In contrast, the rate of fat oxidation is highest during moderate activity such as easy jogging (65% of VO2 max). At such an intensity, plasma free fatty acids and intramuscular triglyceride contribute equally to the overall rate of fat oxidation. During high-intensity exercise (85% of VO2 max), the rate of total fat oxidation falls, mainly because the appearance of fatty acids into the plasma is suppressed. At the same time, lipolysis of intramuscular triglycerides does not rise substantially when exercise intensity increases from 65% to 85% of VO2 max. This would not affect recreational athletes because most cannot sustain high-intensity exercise for more than 10 to 15 minutes without accumulating high (greater than 10 mM) concentrations of lactic acid in the working muscles and blood, which would cause discomfort and stop activity.

When low-intensity exercise continues more than 90 minutes, the pattern of substrate metabolism changes little relative to the first 20 to 30 minutes of exercise. The same is true of moderate-intensity exercise (65% of VO2 max): the rate of total fat or carbohydrate oxidation changes little after 2 hours of jogging or cycling at this intensity compared with the first 30 minutes. However, this level of exercise induces a progressive increase in the mobilization of fatty acids from peripheral adipocytes into the plasma (1). Therefore, the contribution of intramuscular substrates (triglyceride and glycogen) to total energy expenditure probably decreases when the duration of moderate-intensity exercise increases beyond 90 minutes.

[mps]

Now I'm confused again. I posted a question on a recent 'metabolic advantage of low carb' thread about whether there was a difference between ketosis (exercise or dietarily induced) and burning FFA's in your mitochondria without a ketone in sight. Somebody replied with quotes from some biochem texts which stated quite clearly that FFA metabolism directly in your mitochondria is a quite distinct metabolic energy pathway to ketosis. They both end up using acetyl CoA in cells, but get there via different metabolic pathways. Ketosis is very inefficient, which makes it such a star turn for weightloss, whereas free fatty acid burning in mitochondria is a very clean burn. Particularly because direct FFA metabolism in cells does not produce lactate as a by product as glycogen does. Both metabolize fat of course, just differently. So can you be burning just fat for energy, no glycogen, and not be in ketosis at all, particularly when you low carb long term? MPS and Built, HELP!

Your body will adapt over time to be able to use FFA instead of ketones. So less ketones are needed/produced as time goes by.
Your body can use protein to produce glucose and even glycogen to some extent.
Just because your don't show ketones on the urine strip doens't mean you're not in ketosis. It just means that you don't have many excess ketones that your body is being forced to dispose of. (This may(??) negate this aspect of the metabolic advantage over time. You would still have the high cost of converting protein to glucose though)

[fodus8]

I think the confusion here is about ketosis and fat burning. If you are in ketosis then you are burning fat incompletely and producing ketones. If your not in ketosis that does not mean that you are not burning fat. It's all the same fat... just used completely in the Krebs cycle (fat burning/ATP/energy producing pathway) or not. Your workout will have no effect on this. It will just speed up whichever fat burning process you are in.

Your question is difficult to answer without me knowing what you know about the causes of ketosis and fat metabolism. But anyway, as far as fat burning... it's all the same fat and the same process, workout or not. The workout will just make it happen at a faster rate because you need the energy at that time.

MPS this has been REALLY REALLY helpful! I guess the long and short of it is that FAT is FAT to the body but Ketosis generates the Ketone by-product and exercise does not.

So one could say that exercise produces a more clean-burning FAT??

Thanks for all the patience and help.

[fodus8]

This seems like a pretty good article on Fat Burning During Exercise. Even gets into a paragraph or two talking about High-fat diets and exercise.

http://www.physsportsmed.com/issues/1998/09sep/hawley.htm

thanks again!!!!

[fodus8]

I forget where I first found this article. Maybe on the nytimes.com site:
Very cool stuff - if you're into lactic acid!

August 23, 2004

The misconception that lactic acid is a harmful waste product began with the work of a Nobel laureate. In 1929, British physiologist Archibald Hill analyzed muscle fibers of frogs and suggested the lactic acid that pooled in the frog muscles after flexing causes fatigue. But researchers now realize the experiment was flawed. Hill studied the frog muscles in isolation, so he couldn't know that within the body, lactic acid is taken up and consumed as a fuel.

But people like Brooks have since shown that lactate from lactic acid is a valuable fuel derived as the body breaks down carbohydrates. Not only do muscles consume it eagerly, the brain and heart also suck it up from the bloodstream to keep systems running. High levels of the stuff can cause some sensation of muscle burn during exercise (thanks to the hydrogen ions that are released when lactic acid is broken down into lactate), but it doesn't stick around long after activity.

And now, new research shows that lactic acid serves as more than a fuel. In a study, appearing in the journal Science, Stephenson and others show lactic acid actually help keeps muscles running when they might otherwise become sluggish. To understand how, it's useful to look at what makes a muscle flex in the first place.

Thomas Fahey, an exercise physiologist at California State University in Chico, explains that muscle actions are triggered by a mechanism known as the sodium-potassium pump. The sodium-potassium pump moves sodium ions out of a cell while pushing potassium ions in. The difference in levels of each kind of ion creates an electrical charge. Muscle cells use this charge to respond to elecrical signals coming from nerves and to contract. For every two potassium ions that are pulled in from outside the cell, three sodium ions are moved to outside the cell.

When a muscle is working hard, potassium ions can start to leak from the muscle cells and accumulate on the outer membrane. This creates an imbalance and stifles muscles from firing. Chloride ions also start to act as a natural braking agent. By testing muscle fibers of rats, Stephenson and colleagues showed the presence of lactic acid counteracts this braking effect and keeps muscles firing.

"It is a very clever trick," said Stephenson, explaining the acid enables "impulses to keep exciting the muscle when they would otherwise fail."

The finding is one more step away from old misperceptions about muscle fatigue and lactic acid and could be used in ways to help athletes prepare their bodies for competition. Stephenson suggests, for example, that doing short sprints during warm-ups for an event could help an athelete's performance by increasing levels of lactic acid in the muscle and preparing the muscle for a buildup of potassium ions.

[fatburner]

[QUOTE=

I think my question of exercise and ketosis is very difficult to explain.

1. When I exercise I'm burning different types of fuel. Stored glucose and FAT are two such fuels (I think).

2. When I'm following Atkins my body is also burning FAT for fuel. Ketosis.

OK: My question is: Does the body break down, process, etc, FAT fuel differently in these two cases or is the FAT fuel all the same to the body?

Does the body say: "Hey, we've got some FAT for fuel, a FAT is a FAT, is a FAT. Let's get to work." Or does it say, "Hey this is exercise FAT and it's way different than Ketosis FAT."

Does that make sense?[/QUOTE]




Interesting stuff isn't it Fodus8? . Btw. I for one will congratulate you on seeing the light. 7 month's into L.C and you are feeling great. Fantastic! Wait till two years+. I can't believe how well I feel (and that's on 15 - 25 /day cho.) Anyway your point 2. : 'When I'm following Atkins I'm also burning fat for fuel. Ketosis' got me thinking. My question in the post just prior to yours was precisely about this. MPS's reply just after your post reassures me that Ketosis is in fact not the only way of burning fat for fuel. Early on in lowcarbing (and for that matter after a good nights sleep on a 'normal diet') your liver produces ketones from FFA's (which may have been liberated from your own body fat stores by the catabolic hormone Glucagon, or might also be from dietary fat intake -ie. your last fat containing meal) This is true during exercise or not. But ketosis is not a particularly efficient fuel during exercise. Which is why glycogen stores (either muscle or liver) are so important for the non longterm low carber. But the longer you spend low carbing the better all your cells (muscle included ) become at using FFA's directly in your cells' mitochondria (engine room) WITHOUT ANY KETONES. This is so important I'll say it again. NO KETONES. My endurance and strength have both improved considerably since I started low carbing, and I actually do LESS cardio and weights than prior to L.C. The cardio improvement I put down to this direct FFA burning (NO KETONES ;) ) increasing with long term L.C. And the strength improvement I would explain by my endocrine system working so much better with very low carbing that my normal production of HGH has been restored. I'm sure I could have achieved this increase in strength by just pumping more iron and not low carbing. But there are so many other benefits to low carbing anyway that if I can achieve the same physique improvements just by low carbing with less sweat, it's a no brainer.
So your question 'Does the body say: "Hey, we've got some FAT for fuel, a FAT is a FAT, is a FAT. Let's get to work." Or does it say, "Hey this is exercise FAT and it's way different than Ketosis FAT." ' depends on how long you've been low carbing. Most exercise physiologists don't know about the strength/endurance benefits of prolonged very lowcarbing (without any refeeds ) so they don't even include the possibility. And competitive athletes are not interested in sacrificing the time taken for this metabolic adjustment.
What they(the exercise physiologists) do know is that in the short term on low carb diets, and for ever on 'normal' high complex carb diets high intensity exercise depletes muscle and liver glycogen very quickly and exhaustion and muscle soreness is the result. If you train your muscles to burn FFA's directly with a very low carb diet (and my guess is that it takes at least a year) you have a different very powerful way of fueling those same muscle cells. And the bonus is that if you really do have to win the race, you get to use muscle and liver glycogen anyway. I'm no exercise physiologist but my guess is that competitive athletes would maximize their physiological performance (mental factors are a different discussion) by carbing up ONLY on competition eve and NEVER prior to a workout. Like most things, patience is the key. But every day you spend low carbing , your mitochondria get better at using free fatty acids directly (have you heard the music yet? NO KETONES). So wether you want to win races or just look good naked ;) with minimal sweat, or even just to have a longer healthier life, its all about carbs.

[VickiR]

I thought ketones were produced from burning fats - they become significant when there aren't any carbs around, mostly since they then because the sole fuel that the brain recognizes (the brain prefers glucose, but will use ketones in a pinch). The liver can use fats and proteins to make glucose to keep the brain supplied.

Muscles will use glucose, but prefer FFA; over time on a LC plan, they will gear up to use FFA more preferentially. FFA use relies on available oxygen - hence, aerobic exercise (eg., walking) will use FFA. However, muscles do need to have glucose (or glycogen) available for anaerobic exercise (sprinting, weights), which is when lactic acid is produced. Your body (muscles and liver) make a limited amount of glycogen to fuel occasional anaerobic needs.

Excess carbs, beyond manufacture of glycogen and use in the brain, muscle, and other organs, are stored as fat for later use.

This is just my recollection of biochem from a chemical engineer's perspective. A good book to have on hand is Metabolism at a Glance if you are interested - even better is a good intro class into biochemistry.

Also, each of us have slightly different enzymes, which work at differing rates - hence, some of us might be really good at making glucose for the brain (from fats and proteins), or at making glycogen, while others might have more difficulty. We are all individuals - this is why results can vary all over the map.

[realdeal31]

The last time that i been in ketosis i didnt notice any speeded up fat loss, MPS is right, fatloss is all the same.

Plus ketosis just makes me feel so awful, that if i can avoid it i will.

[tom sawyer]

"Ketosis" isn't a biochemical pathway per se, its a term used to indicate a condition where your body is using fat as its primary energy source, and that breakdown of the fatty acids is happening faster than they can be burned through glycolysis. I suppose this happens when you are doing low carb, where you are not feeding your glycolysis pathway as much as your fatty acid oxidation pathway. To my knowledge, all fats are burned in the mitochondria of cells. There is no free fatty acid metabolism, and dietary fat metabolism. All fats are broken down to free fatty acids and glycerol, and the FFAs are then chopped down two carbons at a time to acetylCoA that feeds into glycolysis. When glycolysis can't keep up, the acetylCoA backs up and other ketone by-products are formed that are excreted.

See the first few of paragraphs of this link:

http://www.mun.ca/biochem/courses/1430/lipmethints.html

[tom sawyer]

I would think that the reason some people don't stay in ketosis forever, even though we might keep to induction carb levels, is that our glycolysis pathway adjusts so that it can keep up with the supply of acetylCoA. More than likely, the genes coding for these enzymes turn on and make more enzymes. At this point, we are not excreting as much of our fat wihtout metabolizing it, so we need to reduce the intake a bit to compensate for this.

MAy also explain why some people don't get in ketosis. THeir glycolysis pathways are naturally faster than average, and/or their fatty acid oxidation pathway is naturally slower.

[VickiR]

I thought that muscles could use FFA to produce ATP for their fuel, and did not strictly need glucose. One molecule of glucose produces a lot less ATP than one molecule of a FFA, say, palmitic acid, doesn't it? Dangit, now I need to go look at my books.

[tom sawyer]

What slows glycolysis relative to fatty acid oxidation? Is this regulated by glucose I suppose? So as to provide ketone bodies for feeding the brain?

[tom sawyer]

And does one excrete excess glucose in a manner similar to the wasting of ketones? Is there sugar in our urine? This might speak to which pathway (glycolysis of sugar vs oxidation of fatty acids) is the superior pathway for providing energy for our bodies.

Don't ask me to taste and find out either.

[Built]

Sugar in the urine is an indication of diabetes, and yes, that's the way they used to have to test for it. :p

[ceberezin]

I'm trying to understand what's being said here about ketosis. I had assumed that one had either a fat burning metabolism or a fat storage metabolism, and fat burning necessarily produced ketones. If there were no ketones, you weren't burning fat. From this thread, I am getting that there are three types of metabolism: 1)ketone-producing lipolysis, 2)non-ketone-producing lipolysis, and 3)fat storage metabolism. Is this correct? What puts one in ketone or non-ketone-producing lipolysis? Is it the difference between burning stored fat or dietary fat? Can anyone help me out?

[fatburner]

I'm trying to understand what's being said here about ketosis. I had assumed that one had either a fat burning metabolism or a fat storage metabolism, and fat burning necessarily produced ketones. If there were no ketones, you weren't burning fat. From this thread, I am getting that there are three types of metabolism: 1)ketone-producing lipolysis, 2)non-ketone-producing lipolysis, and 3)fat storage metabolism. Is this correct? What puts one in ketone or non-ketone-producing lipolysis? Is it the difference between burning stored fat or dietary fat? Can anyone help me out?

This difference between ketone producing lipolysis and non ketone producing lipolysis (direct FFA burning in the cells' mitochondria) is what I would like to better understand too . MPS's earlier post seemed to be saying that the FFA non ketone lipolysis always happens, but becomes more and more primary the longer and more seriously you restrict carbs. Otherwise glycogen (from carbs or very inefficiently from gluconeogenesis of protein) will stay the primary fuel source. Two years down the track with very low dietary carbs, and no refeeds, I think I'm a non - ketone FFA burning lipolysis machine. But I only tell my closest friends ;)
So it's time. The longer the better. I've got at least fifty years to play with, but I wish I had started earlier :p . I wonder what I'll be like then? An Inuit would probably know. Sigh! .....I wonder what they would think of L.C. Nutella?

[black57]

Your body almost always produces ketones... it is a normal body function. You really do not need to be in ketosis to produce ketones. Ketosis occurs when you reduce your carb intake and glucagon is activated because of stable insulin levels. When this happens you increase the production of these energy inducing globules, ketones. What isn't used for enrgy is flushed out thru your urine, breath, perspiration. They are harmless by-products of fat.

Tom Sawyer, the only way that there should be sugar in our urine is if there is a serious insulin problem, namely, diabetes. Insulin's job is to shove excess glucose into the tissues. If it is unable to this job, glucose will spill into the urine and extra insulin in the form of a synthetic is prescribed or reduce the consumptions of foods that increase the production of glucose, better known as carbohydrates.

[fatburner]

I know your body always produces ketones. But I think you are mistaken that they are necsessarily involved in fat metabolism. I am interested in the difference between ketone using lipolysis (fat metabolism) or NON KETONE using lipolysis. The non ketone using fat metabolism burns free fatty acids in the mitochondria of cells and has nothing to do with ketones. No ketones are used in this process. No ketones are necessary. NO KETONES. I'm sorry if I sound a little exasperated. Many people still seem to think that fat burning always involves ketones. The factor which apparently determines whether this non ketone lipolysis, or FFA lipolysis predominates is how long and how restrictively you've been low carbing.
Am I right?
Ketone lipolysis is very inefficient - a GOOD thing for weightloss. Non ketone lipolysis (burning FFA's) is at least as efficient as glycolysis and much healthier, but probably not as good for weightloss because of this high efficiency. Which is why the longer you spend low carbing the harder it is to lose, because your cells' mitochondria become better at FFA burning. You get all the other health benefits, but the weightloss slows. It doesn't mean low carbing is 'not working' It's just working more slowly for the same calorie and macronutrient ratio intake. Perhaps it is also why competitive athletes only really start to reap the full benefits of serious low carbing after a couple of years, not the couple of weeks used in most of the research.

[Grimalkin]

Hmmm... I've been suspecting that my body has become very efficient at burning fats, I've been LC-ing for 2 years now. I've been watching calories lately and am starting to finally see some shrinkage!

What I'm wondering though, does this mean that I will have to watch calories for the rest of my life, or else my body will efficiently pack the pounds back on using those FFAs? When one is eating high fat that isn't a very large volume of food! Or will keeping my insulin levels low help prevent re-storage of excess macronutrients? What's the experience with this of you super-fat-burners?

[tom sawyer]

Fatburner, all of the fatty acids in a fat molecule are burned in the mitochondria of cells. Thats where fatty acid oxidation occurs. And they are all broken down into two-carbon molecules and shuttled into glycolysis/Krebs cycle to be completely burned. The only difference you have when you are doing low carb is, your fatty acid oxidation enzymes are working faster than your glycolysis enzymes, so you get a buildup of acetylCoA and this leads to formation of ketones rather than them being used more completely. Normally, you are not burning as much fat so you don't overload your glycolysis enzymes with acetylCoA, therefore there is much less of this to be converted to ketones.

It is interesting to me that our systems are less efficient at converting fat to energy, than we are converting carbs to energy. I would think that we would not want to waste good carbon at a time when we were low on it. It makes me think that the fat-burning pathway was not meant to operate only in starvation mode, but during times of plenty when fat (the best calorie source) was plentiful. When you had plenty of fat, you could afford to waste a little.

[ceberezin]

It makes me think that the fat-burning pathway was not meant to operate only in starvation mode, but during times of plenty when fat (the best calorie source) was plentiful. When you had plenty of fat, you could afford to waste a little.

I suspect you are right. To call fatburning starvation is to make an assumption that we're not supposed to be burning fat. There's another way to interpret this. Our bodies operate in either a resource rich mode or a resource poor mode. Fat and protein are our bodies' preferred source of fuel and building blocks. When we're eating mostly fat and protein and few carbohydrates, we're in resource rich mode. Our bodies do not need to be economical because there's no shortage of fat and protein.

As soon as the amount of carbohydrates begins to climb, our bodies shift into resource poor mode. The preponderance of carbohydrates means that our preferred fuel source is not available, so it's time to conserve. The insulin stimulated by the carbohydrates prompts our bodies to convert those carbohydrates to saturated fat and store it as adipose tissue as a hedge against continuing poor resource conditions. When we reduce the carbohydrates and go back to eating fat and protein, resource rich conditions,we no longer need those fat stores, so we burn them off.

This idea might also explain why our bodies are efficient at burning glucose--get rid of the stuff as soon as possible and make sure it is completely used up because we have to be economical in resource poor mode.

[fatburner]

Fatburner, all of the fatty acids in a fat molecule are burned in the mitochondria of cells. Thats where fatty acid oxidation occurs. And they are all broken down into two-carbon molecules and shuttled into glycolysis/Krebs cycle to be completely burned. The only difference you have when you are doing low carb is, your fatty acid oxidation enzymes are working faster than your glycolysis enzymes, so you get a buildup of acetylCoA and this leads to formation of ketones rather than them being used more completely. Normally, you are not burning as much fat so you don't overload your glycolysis enzymes with acetylCoA, therefore there is much less of this to be converted to ketones.

It is interesting to me that our systems are less efficient at converting fat to energy, than we are converting carbs to energy. I would think that we would not want to waste good carbon at a time when we were low on it. It makes me think that the fat-burning pathway was not meant to operate only in starvation mode, but during times of plenty when fat (the best calorie source) was plentiful. When you had plenty of fat, you could afford to waste a little.

That's interesting Tom S., and starting to become clearer.... But I thought ketones were only formed in the liver. So does this build up of AcetylCoA happen in the vicinity of each cell's mitochondria, and then get transported back to the liver in the blood so that the ketone thing can happen? Why doesn't the AcetylCoA just hang around each cell and be used when it is needed, much like glycogen? Is it because of the: 'when fat was the more plentiful' hypothesis (fascinating idea)? I realize that glycogen is also stored in the liver as well as the muscle cells. I'm starting to hear the old biochem line: 'fat can only burn in the presence of carbohydrate'. But what I think you are saying is : 'Fat can only burn in the presence of carbohydrate, OR KETONE FORMATION WILL OCCUR (my italics). What's the minimum ratio of glucose to AcetylCoA in the Krebs Cycle before ketone formation starts to happen? And does this ratio change with long term low carbing? In other words, does x amount of burnt FFA result in the formation of y number of ketones in the absence of glucose? Are you saying that the two carbon molecules that form from the complete oxidization of FFA's can't get into the Krebs cycle without some glycolysis too? Or just that without glycolysis a certain number of ketones must be produced. So even after say twenty years of induction levels of carbs, I would still necessarily be producing the same ratio of ketones as a by product of FFA burning . You seem to be saying that the better your cells become at FFA burning the more ketones are produced as well (I mean that [in the absence of glucose] a burnt FFA always produces x no of ketones). But muscles (particularly for instance heart muscle) can burn ketones for energy too can't they? So what are the by products of burning a ketone? I mean if FFA burning (in the absence of glucose) always results in ketone formation, what does ketone burning (presumably also in the absence of glucose) result in? And can the Ketones that are produced when FFA burning produces too much AcetylCoA then be used again by the same muscle cells that just burnt the FFA?
I think I'm totally confused!
Just to use myself as an example. I've been induction lowcarbing for over two years now. I've never been in 'measurable' ketosis. I realize that not being measurable doesn't mean ketone formation, even in large amounts, is not happening. Just that they being used rather than excreted. But then I've never had body fat to lose. I've really upped the fats and actually reduced the protein compared to before low carb. I eat much less food than I did before, because I don't get hungry like I used to, but I suspect that I wasn't even absorbing a lot of the pre - low carb food (not just the carbs either!). But I'm putting muscle on very slowly while working out much less than I did before. My muscles must be getting better at burning FFA's, because my endurance is improving gradually as well. I certainly don't think these strength/endurance improvements will go on indefinitely without at some stage having to up my work rate. Just that at the moment the amazing health benefits of just severe low carbing seem to be enough.
Anyway, so you're saying that I must be producing more ketones also as a result in direct and inviolable proportion to the amount of FFA burnt for energy (without glucose being involved), and then presumably using those ketones perhaps in my brain and heart rather than excreting them?
If all this sounds like total nonsense, perhaps you could simply explain the difference between a ketone and an FFA being burnt in a muscle cell for energy?
Sorry to fire so many questions at you. I'd really like to understand this ketone/ FFA thing properly.

[ItsTheWooo]

Maybe someone can post a link or an answer to this question which I was thinking about the other day. Sorry if this has already been asked.

I was at the gym thinking about how exercise burns fat (I actually don't really know exactly how it works - exactly.)

Question is: Is the body's fat burning process the same in exercise as it is in ketosis?

It seems to me like the body would have to go through the same steps to burn fat whether it's through exercise or ketosis (whatever exactly that process is.)

The way I understand it is when a person exercises, stores of glucose and fat are being burned for fuel.

If exercise and ketosis are handled the same, wouldn't that automatically make the Atkins diet good for you?

Any thoughts?
It's important to remember you can burn fat without being in "ketosis". All being in ketosis means is that you have a really high concentration of ketones in the body. This high concentration can be caused by eating an extremely high fat diet, by fasting totally, or by being sick.

Everyone has ketones in their body at any given point, even your friend who eats carbs all day. If you are eating fat at all you will burn fat for fuel and ketone bodies will result. If fat is the smaller percentage of your energy stores (due to lack of energy deficit and low dietary intake), then you will obviously have less ketones in your body than someone who uses fat as a larger percentage of energy (someone creating an energy deficit and/or high percentage of dietary intake of fat).

So, if you are creating a demand on body fat by exercise, that body fat will be burned the exact same way as any other lipids. Ketone bodies will result.

Using ketones for energy is a perfectly natural process. Detractors seem to think there is something unhealthy or unnatural about using ketones as a preferential/primary fuel source, however, which is why people will say Atkins (induction) isn't good for you. There's a lot of misconceptions about a fat based metabolism, namely some "experts" are afraid of mineral problems on a low carb intake which could theoretically lead to ketoacidosis. The claims are largely unfounded, if someone is eating a nutritionally adequate high fat diet ketoacidosis is not a risk or concern for a healthy person anymore than hyperglycemia is a concern for a healthy person eating a high carb diet. Healthy bodies can keep our ketones in check, just as a healthy body doesn't become hyper/hypoglycemic from sugar.

[ItsTheWooo]

I know your body always produces ketones. But I think you are mistaken that they are necsessarily involved in fat metabolism. I am interested in the difference between ketone using lipolysis (fat metabolism) or NON KETONE using lipolysis. The non ketone using fat metabolism burns free fatty acids in the mitochondria of cells and has nothing to do with ketones. No ketones are used in this process. No ketones are necessary. NO KETONES. I'm sorry if I sound a little exasperated. Many people still seem to think that fat burning always involves ketones. The factor which apparently determines whether this non ketone lipolysis, or FFA lipolysis predominates is how long and how restrictively you've been low carbing.
Am I right?
Ketone lipolysis is very inefficient - a GOOD thing for weightloss. Non ketone lipolysis (burning FFA's) is at least as efficient as glycolysis and much healthier, but probably not as good for weightloss because of this high efficiency. Which is why the longer you spend low carbing the harder it is to lose, because your cells' mitochondria become better at FFA burning. You get all the other health benefits, but the weightloss slows. It doesn't mean low carbing is 'not working' It's just working more slowly for the same calorie and macronutrient ratio intake. Perhaps it is also why competitive athletes only really start to reap the full benefits of serious low carbing after a couple of years, not the couple of weeks used in most of the research.

Interesting theory... so you believe that your body can get better at using FFAs for fuel over time. This adaption to burning fat makes it harder to lose weight on LC, because direct FFA usage can make your body use fat more like sugar (instantly without lengthy conversion processes (into ketones), processes which hog energy and increase total metabolic rate making it easier to lose weight). Am I correct?

If this is what you believe, what is responsible for your body "learning" to use fats more efficiently? I imagine it must have something to do with hormones and enzymes etc... is this just a theory up in the air or is there real evidence to support it?

[tom sawyer]

Wooo, although I know of no specific studies dealing with metabolic adaptations to a low carb diet, it is certainly easy to believe that our metabolisms adapt to this way of eating. Control theory tells us that nearly all the enzymes in a pathway are feedback regulated, so as to maintain a steady throughput and avoid buildup of a particular intermediate. If a buildup of acetyl CoA was a consequence of an abnormal dietary situation (ie, eating too much fat to where glycolysis is not "keeping up"), you would quickly see glycolytic enzymes activated to work faster, and/or activation of the genes encoding the enzyme proteins resulting in more enzymes. This is how the pathways adapt to varying levels of substrates. The regulatory mechanisms are quite sophisticated, and the pathways are interconnected at multiple steps. The result being, everything affects everything else and you have a system that can deal with a great variety of inputs (everything from an apple to a zuchini) with the same output (a healthy functioning individual).

The fact that we can be in ketosis and have elevated levels of ketones in our systems for a prolonged period, just proves that it is normal for such chemicals to be present in our systems. Otherwise, our biochemical pathways would quickly adjust to eliminate thes intermediates from our systems. The ketones are there for a reason, to supply the brain with an energy source in the absence of glucose.

I'm still trying to review my biochem to see just where all this stuff happens.

[tom sawyer]

OK I went and did a little review (its been a long time since biochem class).

First of all, ketone bodies ARE only formed in the liver (yeah you were right, get over it). They are formed from acetyl CoA, which is the breakdown product of fatty acid degradation. Ketone bodies are formed when carbs are low, because when carbs are low so is an intermediate in the Krebs cycle (oxaloacetate, it is used for making glucose). Without OAA, the acetylCoA can't get burned on up in the Krebs cycle. So the liver turns this into ketone bodies and ships them out in the blood. The ketone bodies are then carried to other tissues for use as energy.

The info I read said muscle could use ketone bodies, but the brain requires glucose (also heard this is not entirely the case but haven't researched this yet). Supposedly, when glucose is low the ketone bodies are made to feed muscle and thereby spare what glucose there is, for the brain. Don't know if thats true, but we ARE making glucose via gluconeogenesis. I think our blood glucose levels are on the low side but measurable (and stable, which is nice.) The liver lacks the enzymes to metabolize ketone bodies, which is why it can make them for export.

Fatty acids are oxidized to acetyl CoA in other tissues like muscle. In these tissues, acetyl CoA feeds into the Krebs cycle and electron transport and is used to generate energy (ATP). The ketone bodies are also broken back down to acetyl CoA and fed back into the Krebs cycle for energy. How much of each a muscle uses, I don't know. I'm supposing ketone bodies make a significant contribution to muscle energy needs, otherwise why have the pathway?

Since we still have glucose in our systems (although not a large store of glycogen in our livers), I'm assuming our muscles still utilize glucose as an energy source to some degree. So we have some glycolysis going in our muscles, in addition to the Krebs cycle/electron transport.

One thing I'm realizing, is that the liver is a key organ in energy storage and metabolism. It is the place where glucose is stored in times of plenty, where it is made in times of little carbs, where fatty acids are converted to ketone bodies in times of fat but no carb, and where glucogenic amino acids are converted to glucose in times of protein but no carb. Theres a lot going on in the liver. Makes me ashamed I periodically pickle it with liquor.

To answer some of your specific questions, when a ketone body (which is acetoacetic acid, hydroxybutyrate or acetone) is burned in a cell, it is first converted back to acetyl CoA (which is what it was made form in the first place). This is then turned into energy (ATP and/or reducing power) and carbon dioxide in the Krebs cycle.

As for you not testing positive for ketone bodies, as I understand it the strips only detect one of the three ketones I mentioned. Maybe you happen to produce more of the others. Or maybe as you suggest, you are using most of your ketone bodies for energy, which would be the case if you are not eating a whole lot of calories.

I'll quit now, before I get in any deeper. Hope this adds to your understanding of whats going on at the molecular level.

[tom sawyer]

Here are a few references I googled up to brush up on my biochem. Don't know how this reads but have at it.

http://www.rpi.edu/dept/bcbp/molbiochem/MBWeb/mb1/MB1index.html

http://www.mun.ca/biochem/courses/1430/lipmethints.html

http://web.indstate.edu/thcme/mwking/fatty-acid-oxidation.html

[ceberezin]

Thank you, Tom Sawyer. Your explanations are lucid and helpful. I especially appreciated your discussion of self-regulating enzymatic pathways. I have learned a good deal by participating in this thread.

[fatburner]

Thank you, Tom Sawyer. Your explanations are lucid and helpful. I especially appreciated your discussion of self-regulating enzymatic pathways. I have learned a good deal by participating in this thread.

Yeah Tom S. , many thanks. This thread is fascinating. I too have learnt a great deal. I really should apologize for sounding a bit sure of my facts a few posts earlier. I think I'm beginning to appreciate just how complex this whole short/medium and long term adaption of lipolysis to low carbing is. I do want to understand why I feel so amazingly well the lower and the longer I spend low carbing. It's starting to be a bit intoxicating. I think I've spent most of my life in a kind of carb induced stupor. Everything, and I mean everything - body wellness, memory , mood , relationships , sleep, dental, and (yes I have to say it , even sex) - it's ALL getting better. If this was as good as it gets, I'd be a happy man. But low carb bliss seems to be becoming a journey, not a destination. I keep hoping it's even half as good for all you other low carbers as it is for me. It would be truly appalling if I was the only one....

Moving right along, you said that cells can re-use the ketones that the liver has made from the excess AcetylCoA that the mitochondria have made from the FFA. And when a ketone gets sent out by the liver and is converted into AcetylCoA in this kind of 'secondary burn' , presumably this secondary acetylCoA also needs some glucose involvment for the Krebs cycle to work? I'm still wondering wether the amount of glucose the Krebs cycle needs per unit of AcetylCoA reduces with long term low carbing, so that (a) more of the AcetylCoA that mitochondria make from FFA's is used for creating energy and not redirected to the liver to be converted into ketones ; and (b) the only ketones the liver really needs to make are those for the brain and heart. And I presume the liver can make it's own ketones directly from FFA's rather than waiting for excess AcetylCoA to arrive back from other mitochondria?
As you said, the liver's role in making ketones from the excess AcetylCoA from FFA burning is pretty central to lipolysis, at least early on in low carbing. But I'm really curious about whether the mitochondria actually get better at using the AcetylCoA they make from FFA's without needing as much glucose if their ongoing supply of glucose is limited by long term lowcarbing? I'm afraid I get a bit impatient with most of the biochem texts, because they treat carb restriction as short term 'starvation' and not a desirable long term transition. I think we need some Inuit Biochemists!

Questions, Questions , Questions.
Btw. Be nice to your liver!

And Woo. I was hoping that this was well established biochemical fact. I noticed in another thread somebody mentioned that competitive athletes become much better at burning FFA's directly in muscle mitochondria. That is presumably not even a low carbing adaption, but a training one. My speculation is that prolonged low carbing probably has the same effect. It certainly has with me, and I'm not a competitive athlete ;) , but I was hoping one of this forum's biochem gurus could explain it a bit. Most people say their weightloss slows as they approach goal. But I wonder whether this is the same process as somebody who is still nowhere near goal but has been low carbing for an extended period and finds the weightloss slows. It's worth repeating that even if this is in fact the case, the amazing health benefits of low carbing, would make it a sensible lifestyle choice anyway, even if you only lose slowly. Not that any of this will be generally accepted for a long time. Professional opinion still hasn't worked out that low carbing is the most effective, (regardless of wether it is the healthiest way to eat, period) way to lose weight. Sigh!
I think the thread that is discussing moderate carb cycling (LCanita et al)is very interesting in this regard. Maybe some of their success in keeping the weightloss on the boil is because the gentle carb cycling stops their mitochondria getting too efficient at burning FFA's. Rivetting stuff, isn't it?

[tom sawyer]

The liver is a primary site for fatty acid oxidation, and it makes ketone bodies out of fatty acids (via acetyl CoA) when there is plenty of fat but not much carbs. It must be the case, that muscle cells do not have the same biochemistry going on, otherwise they would be pumping out ketone bodies too. I don't think muscle makes ketone bodies. It simply is able to burn free fatty acids via oxidation/Krebs, and ketone bodies from the liver via the same basic mechanisms. Obviously low glucose does not inhibit acetyl CoA from being used in the Krebs cycle, in muscle. Part of this, may be due to the fact that low carbing does NOT cause extremely low blood glucose levels. I assume this is because the amount of carbs you eat isused to maintain blood glucose levels, and also the protein is converted to glucose in the liver (some amino acids can be converted to glucose). I still haven't researched whether the brain can use ketone bodies, I guess it doesn't have to since we low carbers still have blood glucose in our systems. I also haven't seen what sort of blood glucose levels we typically run on induction level carbs. It must be on the low side of normal, but my guess is its well above zero. Healthy blood glucose is like 100mg/dcl right? My diabetic friend tries to get hers below 110.

On the subject of feeling better, I think that is due to not carrying around as much extra weight. It is a LOT of work to tote around an extra 40+ lbs. I beleive diet allows you to lose weight, to a point that you are then able to be more physically active without it being too taxing to yur system. A snowball effect in the right direction. This is my personal experience. I know others think exercise is more fundamental to their weight loss.

On the subject of slowing of weight loss, I've thought a bit about this and here's where I'm at. We all start our diet program from a different point. Our pre-diet eating habits have stretched our stomachs to different degrees, and we are used to eating a certain amount of food. We are also used to eating a certain composition of food. I think that the more carbs you were eating before starting your diet, the better you'll respond to the diet initially. This is because your apetite will change most drastically, and you will consume a lot fewer calories than you were before. At some point though, you will get used to eating an amount of calories that is enough to stall your weight loss. At this point, you can get used to eating this amount of calories, and then work on portion control as phase 2 of your weight loss. Since you are now a smaller person, you SHOULD be able to train yourself to eat less with less effort than when you were supersized.

I admit that there is probably also a metabolic advantage to a low carb diet, and you are probably right that this advantage is attnetuated with time. Might always be a small advantge, but my guess is that the body adapts and becomes more efficient over a matter of months. Stands to reason, although when you consdier that we are eating a diet that signals a time of plenty, we may never have the need to be as efficient.

I think there is merit to the idea that carb cycling may allow a replenishing of intermediates in the Krebs cycle (or other metabolic processes), so that optimum fatty acid oxidation may proceed. Its also possible taht carb cycling is the most satisfying way of eating for these people, such that their consumption is the lowest. Yes, I'm still someone who believes thta calories count. Although, I realize that a calorie is ot a calorie, given the differences in digestion, absorption and utilization.

It is fun to pretend that we know why low carb works. Almost as fun as hearing the experts trying to reconcile our success with their wrong dogma.

[fatburner]

Tom S. I'm reasonably sure that your brain can adapt fairly quickly to about 85% ketones 15% glucose. I wonder if anyone ever tested a traditional diet Inuit for neurological ketone/glucose utilization?
cheers

[tom sawyer]

I'd just like to know what an Atkins induction dieter runs for blood sugar. I'll see if I can find out. Just because we don't eat carbs, doesn't mean we aren't making them as we need them. Gotta do something with the protein anyway.

BTW, there are glucogenic amino acids and ketogenic amino acids. Meaning some can be converted to pyruvate and then to glucose (gluconeogenesis), and others can be made into Krebs cycle intermediates.

[cbcb]

I suspect you are right. To call fatburning starvation is to make an assumption that we're not supposed to be burning fat. There's another way to interpret this. Our bodies operate in either a resource rich mode or a resource poor mode. Fat and protein are our bodies' preferred source of fuel and building blocks. When we're eating mostly fat and protein and few carbohydrates, we're in resource rich mode. Our bodies do not need to be economical because there's no shortage of fat and protein.

As soon as the amount of carbohydrates begins to climb, our bodies shift into resource poor mode. The preponderance of carbohydrates means that our preferred fuel source is not available, so it's time to conserve. The insulin stimulated by the carbohydrates prompts our bodies to convert those carbohydrates to saturated fat and store it as adipose tissue as a hedge against continuing poor resource conditions. When we reduce the carbohydrates and go back to eating fat and protein, resource rich conditions,we no longer need those fat stores, so we burn them off.

This idea might also explain why our bodies are efficient at burning glucose--get rid of the stuff as soon as possible and make sure it is completely used up because we have to be economical in resource poor mode.

Wow, this if true is pretty insightful. I've never heard anybody put things that way... it's been more of the 'body switches into emergency mode with ketosis' line of thinking. :rolleyes:

If you go way back historically, it could make sense in a hunter-gatherer paradigm. (Of course, everything's a theory.) In essence it's suggesting that if you were in a rich hunting ground with adequate meats and the animals themselves were well fed, then life was good. But that early on in evolutionary terms (at least for some populations) resorting to making breads out of grains and eating mostly roots and other non-meat non-fish items meant you were scrounging and life was not good.

[cbcb]

It is fun to pretend that we know why low carb works. Almost as fun as hearing the experts trying to reconcile our success with their wrong dogma.

Heh, thanks for the nicely-put daily dose of cynicism borne of burgeoning incredulity. :D

[bluesmoke]

Very good stuff, Tom Sawyer. According to Dr Mary Enig, short and medium chain fatty acids can be broken down directly in the mitochondria, only long chain fatty acids go through the whole ketone cycle. Our bodies store fat as long chain faty acids. Atkins cites studies done on brain tissue at Harvard Medical as showing that most of the brain can not only function well on ketones, be actually seems to function better than on glucose. Nyah Levi

[Debbyd]

I hope you get a lot of responses to this. Its a good question. Recently I bought a scale that measures body weight and body fat. I have been weighing every morning and my weight is going down, but the fat percentage was going up until I started being more active. I still have a long way to go. I don't want to stay at 30% body fat.

Mary,

Where ever did you get that kind of scale. Does it take a rocket scientist to work? I need simple. Debby