dietar fat storage?

[meburke]

Somewhere, I think in a book on managing energy (that I've since lost), I got the impression that the body only converted carbohydrates to body fat and that protein and dietary fat were burned as energy.

Does anyone have an authoritative link to this subject?

Thanks,

Mike

[LisaS]

hard to explain glycolysis, glycogen storage, gluconeogenesis, cori cycle, etc. if the body never burns glucose

maybe you are mis-remembering what this book said or the context in which it was said? was it maybe trying to address what happens to macronutrients in excess of caloric requirements rather than cellular metabolism in general?

[meburke]

I believe the point being made in the book was that calories from excess fat were burned, or that only fat calories needed for energy were absorbed, but that is why I wanted a link: I read the book so long ago that I can't remember the statements and arguments clearly.

Mike

[LisaS]

I'll defer to Gabe here [Mr. Adipose Tissue Metabolism] what I think/remember as facts and what research has shown to be true may be two different things and I don't want to lead you astray w/out doing some research (which I can't do right now)

[Gabriel Guzman]

I believe the point being made in the book was that calories from excess fat were burned, or that only fat calories needed for energy were absorbed, but that is why I wanted a link: I read the book so long ago that I can't remember the statements and arguments clearly.

Mike

I haven't read a book or an article that would argue that the absorption of fat depends on the calories neede for energy. If that were the case, we wouldn't accumulate fat, which is the result of not having an energy demand higher than the energy we can store.

Whenever energy is needed, the body does what it needs to so the energy demand is supplied regardless if it needs to draw from fat, protein or carbohydrate. However, depending on the availability of fuel sources, then one of them is used in more than the others.

What people normally learn (int he worse case scenario), for example, is that glucose (from carbohydrates) is the only source of energy for the body, hence we need a lot of it. Glucose is a quick source of energy and if available, the body will use it quickly as well. When carbohydrates are reduced but there is enough fat available, the body switches to use more fat for energy, sparing glucose for tissues that can't use anything else. Fortunately for us, those tissues are very few, mainly red blood cells and some, but not all brain cells. The rest of the tissues, except for the liver, adjust to the use of ketone bodies, which result from fat oxidation, as their fuel. Does it matter if it is dietary or stored fat? In terms of using it for energy it really doesn't. In terms of creating an energy deficit so it is the fat in store what is used mostly, then the fat coming from the diet doesn't need to be excessive. When fat is in enough supply in the fat stores, provided that the metabolic scenario favours fat oxidation, the body will spare the use of protein, except for keeping blood glucose levels constant during overnight fast, for example.

Some people tend to think that protein is readily used for energy. It's not. That's why ketones exist, to spare protein from being used for the sole purpose of energy production so they can be used for gluconeogenesis when blood glucose needs to be maintained constant. In extreme cases, prolongued fast which leads to true starvation, proteins can and will be used.

The body will absorb everything it needs, whether it uses it for energy or not. So, is not that the body will absorb only calories from fat, which by the way is a misleading concept as the body absorbs nutrients, period, not calories per se, but rather that it will use whatever is readily available and 'ready to be used'. If the energy demand is not supplied by the fat that comes in the diet, it will draw from what's in store. So, immediately after eating, it's unlikely that it is the fat in store what's going to be used right away. But during resting time, fat in store becomes the source of energy provided that there is no food coming in all the time, which is what normally happens for some, thus making them unable to use what they have in store. The other extreme case is somebody extremely lean with very little body fat. The example is a little complicated because somebody extremely lean with good muscle development already has an eficient system to use both, fat and carbohdyrate, but assuming that carbohydrate is limited anyway, then the dependence on dietary fat becomes more evident for energy production.

[LisaS]

it just occurred to me what this might be about - there is a school of thought on internet websites that proposes that excess dietary fat will not be stored as fat tissue (but rather just burned) , excess protein consumed will not be stored as fat tissue (but rather just burned) - only excess dietary CHO will be stored as fat tissue. Maybe this is what the book was attempting to say - which still leaves open if there is any merit in the proposition or not.

[Gabriel Guzman]

Well, 'burning' of fat doesn't depend on how much fat is coming in the diet but under which hormonal influence is the body working. If fat oxidation is inhibited by having high levels of insulin all the time, it doesn't matter how much dietary fat comes in the diet, it will be store as fat internalization is favoured by insulin. If that fat also comes with a high amount of carbohydrate, then fat will be made from excess carbohdyrate, which is also an insulin dependent process. The same goes for excess protein... it is the metabolic scenario what determines if something is made or used.

[meburke]

This is why I wanted an authoritative link. (I can follow the biochemistry.)

Broken-down fat does not enter the bloodstream. (As far as I know, the only fat that gets into the bloodstream from diet is homogenized milk which has such small fat globules in suspension that they can actually pass into the blood and through capillary walls. All other fat is digested first.) As I understand it, a small amount of cholesterol can be absorbed in the intestine, but the nutrients from fat actually are converted to ketones for energy fuel, and if there is no carbohydrate to work with, the keytones are excreted.

I believe the argument was that since fat is NOT passed directly to storage (having to be reprocessed by sugar and insulin), fat, by itself, is not a fat-producing food in the absence of carbohydrates.

So, what I'm looking for is a detailed description, from an authoritative source, that will either support or refute the argument.

Thanks,

Mike

[meburke]

Re-reading Gabriel's long post, it seems to me that maybe I haven't made this clear: I'm only talking about DIETARY fat and dietary carbs and protein. It seems obvious to me that what Gabriel describes is pretty straight forward: The body absorbs macro-nutrients from digestion, and for energy processes ketones first, glucose/glycogen second, converts bodyfat third, and converts body protein as a last resort (in the absence of favored other sources). This is a "simplified" explanation of course. The reason I'm looking for an authoritative link is because I want more than what can be simplified for presentation in this forum.

Thanks again,

Mike

[Gaelen]

Re-reading Gabriel's long post, it seems to me that maybe I haven't made this clear: I'm only talking about DIETARY fat and dietary carbs and protein. It seems obvious to me that what Gabriel describes is pretty straight forward: The body absorbs macro-nutrients from digestion, and for energy processes ketones first, glucose/glycogen second, converts bodyfat third, and converts body protein as a last resort (in the absence of favored other sources). This is a "simplified" explanation of course. The reason I'm looking for an authoritative link is because I want more than what can be simplified for presentation in this forum.

Well, gee, Mike...if you know what you're looking for exactly, there's always Google and PubMed for your searching pleasure. :confused: Seriously...if you're looking for some documented scientific research to substantiate your question and what sounds like your own hypothesis, you might want to do some research on your own. If you do your own searches, chances are you'll get things that are closer to what you're looking for than the information we present here. We're a web group that includes a bunch of very experienced people, but we're not a search engine...and if you're looking for a researched answer, you might need to do a little homework on your own.

Oh wait...that was another month's challenge... ;)

[meburke]

That's a snotty answer, but it still deserves a response.

First, this is not an hypotheses I came up with on my own. About 5-6 years ago I had a book on personal energy management that suggested eating high-protein, low-carb snacks and lunches to boost and retain energy during the workday. The book said specifically that fat was not a factor in energy drain or fat storage because fat could not be stored. In fact, I'm pretty sure the book said that protein and fat were digested and used for fuel (thus boosting energy), and only calories from carbohydrates could be stored as bodyfat. The information on fat absorbed into the blood stream came from another book I read about the same time, specifically addressing myths about high cholesterol. I had over 3000 books at the time, but I've moved twice and over half the books are not readily available to me or I would go back and refer to them. If I could remember the titles, I would look up the books somewhere else.

I did re-read "Protein Power" and the only real thing referred to in the book that I could find was a Question on page 148 (pocket paperback version) "Won't this diet put me into ketosis?" I inferred from the answer that carbohydrates need to be present in a quantity high enough to convert the ketones, but there are no footnotes or references.

Although I can't find any charts or graphs specifically relating to this question I did find some pretty good sources on the net at Lippencott:

http://connection.lww.com/Products/smith/documents/PDFs/Ch01.pdf
http://connection.lww.com/Products/smith/documents/PDFs/Ch07.pdf
http://connection.lww.com/Products/smith/documents/PDFs/Ch21.pdf
http://connection.lww.com/Products/smith/documents/PDFs/Ch26.pdf
http://connection.lww.com/Products/smith/documents/PDFs/Ch37.pdf
http://connection.lww.com/products/rhoades/documents/smch27.pdf
http://connection.lww.com/products/rhoades/documents/smch30.pdf
http://connection.lww.com/products/lieberman/documents/41869%20ch%2003(35-48).pdf (http://connection.lww.com/products/lieberman/documents/41869%20ch%2003%2835-48%29.pdf)
http://connection.lww.com/products/lieberman/documents/41869%20ch%2015(215-230).pdf (http://connection.lww.com/products/lieberman/documents/41869%20ch%2015%28215-230%29.pdf)

I have ordered a couple of these books, and I have found a number of good tutorials and courses online for Biochemistry and Physiology. The links above represent example chapters from different books. The documents are only about 15-20 pages for each one, so they are quick to read if you have the background, and you can get the background from the tutorials. (I had most of the background already.)

My quick history is: I've been doing Martial Arts since I was 14. My weight seemed to stabilize at 210 lbs until I sustained some injuries that kept me from working out, and then it climbed to 240 lbs. (I got it down to 220 lbs in 1995, but knee problems slowed me down after and I climbed back up.) I went on a low-fat diet and gained 40 lbs in 4 years. I read in Phillip Maffetone's book, "The Maffetone Method" that some people seem to be carbohydrate sensitive and low carb diets were better for them, so I researched low-carb diets and settled on "Protein Power" as my guide. I did this because the Eades claimed that everything they put in the book had a sound basis in Physiology and Biochemistry taught to every Physician. I haven't lost any weight (I vary between 270-280 lbs) but I haven't gained any more either.

Why am I so interested in a scientific argument now? I have had some severe muscle stiffness resembling polymyalgia (PMR) for the last 11 months, and the VA hospital finally let me see a Rheumatologist this week. He poked and prodded (I'm pretty sure I have to go to confession tonight) and insisted that I need to get my weight down to under 200 lbs. He claims that the only thing I have to do is watch my calories. If I'm going to discuss this with him rationally, I need to know more than just general specifications on diet.

Why did I come here? I thought there might be a person or two on the forums that were already informed about the processes and knew where to direct me for further study specific to my question. I need to get the answers fairly quickly and this seemed like a possible shortcut.

Is this important to me? YES! I'm so stiff I can't function without Naproxen in the morning and evening, and then I'm still so stiff I can't do Yoga or Martial Arts without hurting like hell. (The Yoga is something I need to do to compensate for the fact that I'm too big. Sooner or later the consequences of not controlling my weight will catch up with me despite the Yoga if I don't make changes.) I need the co-operation of my doctor to alleviate the pain, so I need to lose the extra weight. Although I haven't lost weight on my not-to-disciplined low-carb diet, I have more energy and feel better. My blood pressure, heartrate, cholesterol and insulin levels are very good. (My regular doctor says I'm pretty fit for a fat guy.) I am committing myself to getting my weight down to <200 lbs and 15% bodyfat, and this program looks like the first step in achieving that goal.

I appreciate the help,

Mike

[Gabriel Guzman]

This is why I wanted an authoritative link. (I can follow the biochemistry.)

Broken-down fat does not enter the bloodstream.


Well, then if you've followed the biochemistry, you should know that fat does enter the bloodstream, unless you know of any other way to transport nutrients. What they don't do, however, is to be on their own in the bloodstream, simply because water and fat don't mix. Maybe this is simple and clear enough. In fact, they're carried in chylomicrons, which is a very nice trick for the body to trap fat and transported in an otherwise impossible medium to travel.


(As far as I know, the only fat that gets into the bloodstream from diet is homogenized milk which has such small fat globules in suspension that they can actually pass into the blood and through capillary walls. All other fat is digested first.) As I understand it, a small amount of cholesterol can be absorbed in the intestine, but the nutrients from fat actually are converted to ketones for energy fuel, and if there is no carbohydrate to work with, the keytones are excreted.


What can I say... I don't know where you get your information. Choelsterol and triglyceries are all packed in chylomicrons to be transported to the tissues. They form in the intestinal mucosa and reach the blood via the lymphatic system. Triglycerides are taken up by muscle and adipose tissue. Whatever is left of the chylomicrons are ultimately removed from the body by the liver... but you already know that.


I believe the argument was that since fat is NOT passed directly to storage (having to be reprocessed by sugar and insulin), fat, by itself, is not a fat-producing food in the absence of carbohydrates.


I think your confusion is that you don't know how dietary fat is handled in the intestine, even before entering the bloodstream. Dietary fat is first broken down into something that can be transported Triglycerides that are produced by fat 'diggestion' are, in fact, taken up by adipose tissue and stored there. If excess carbohydrate is also present and energy demands are already met, then lypogenesis can also take place in the adipose tissue. So, of course is not fat that passes directly to be dumped in the adipose cells, but the triglycerides that comprised it. Sugar has nothing to do with fat 'reprocessing'. If by 'reprocessing' you mean fat synthesis, if that is from re-esterification of fatty acids into triglycerides, it is insulin what has a role, not 'sugar'. I think you're problem is that you're taking every line in a literal way. Fat production doesn't depend on the presence of carbohdyrates per se, but on the action of insulin. Now, is clear that excess carbohydrates will definitely provoke an increse in insulin release and therefore all those processes that are insulin dependent or those in which insulin promotes their activity will be affected, including cholesterol synthesis.

One of the sources you provide actually presents this in a nutshell:


Any dietary fuel that exceeds the body's immediate energy needs is stored, minly as triacylglycerol (fat) in adipose tissue, as glycogen (a carbohydrate) in muscle, liver and other cells and, to some extent, as protein in muscle.

So, not my unauthoritative words.

...but the nutrients from fat actually are converted to ketones for energy fuel, and if there is no carbohydrate to work with, the keytones are excreted.

What exactly are 'the nutrients of fat'? Do you mean triglycerides? Ketones come from beta-oxidation of fat, not fat nutrients. And whether ketones are used completely depends on the energy demands of the body. Ketones can't be used as is by the cells. They're first converted into something that can enter the Krebs Cycle, so trusting that you already know that too, I won't go into details. Suffice to say that when carbohdyrates are limited, an in a very simplistic way of saying it, the Krebs cycle moves backwards as there isn't enough pyruvate to be combined with Acetyl CoA to form cytrate. In fact, Acetyl CoA accumulates during beta-oxidation and inhibits pyruvate kinase, while favouring the action of pyruvate carboxylase, which then makes oxaloacetate instead. This intermeidate in the Krebs cycle is used in gluconeogenesis, which in turn is fueled by fat oxidation. So for ketones to enter the Krebs cycle to be oxidized, enough pyruvate needs to be converted into citrate, which happens when enough carbohydrate is present. Pyruvate is a product of carbohydrate metabolism.

What all this means is not that ketones are not used. It means that ketones are used until the cells meet their energy demands. When that happens, excess ketones are excreted. So when people see the deep purple color that makes them believe they're burning more fat, what they're actually seeing is the surplus ketones that didn't enter the Krebs cycle, regardless of how much fat oxidation occured.

From your other post in this thread, we find this:

First, this is not an hypotheses I came up with on my own. About 5-6 years ago I had a book on personal energy management that suggested eating high-protein, low-carb snacks and lunches to boost and retain energy during the workday. The book said specifically that fat was not a factor in energy drain or fat storage because fat could not be stored. In fact, I'm pretty sure the book said that protein and fat were digested and used for fuel (thus boosting energy), and only calories from carbohydrates could be stored as bodyfat. The information on fat absorbed into the blood stream came from another book I read about the same time, specifically addressing myths about high cholesterol. I had over 3000 books at the time, but I've moved twice and over half the books are not readily available to me or I would go back and refer to them. If I could remember the titles, I would look up the books somewhere else.

Let's see... what said book suggested is pretty similar to what we do here; adequate protein intake and carbohydrate reduction. Now, the book goes on saying that fat was not a factor in energy drain (whatever that is) or fat storage because fat couldn't be stored. Yes and no. Fat storage (of course after dietary fat being brokend down in the intestine) requires the action of insulin, but since the food is low-carb, then that proccess is pretty much diminished if the insulin tap is not always splurging the fat cells. Because the metabolic scenario promotes more fat oxidation than fat storage, then that process is not the main activity of the body, but that's far from just categorically saying that fat cannot be stored. In fact, it does and obesity is the outcome of excess fat storage.

Now, your book says that fat and protein are used for fuel. That would actually defeats the purpose of ketones, which is sparing protein from being used for fuel. The actual boos in energy comes from the fact that the energy bang from fat is higher and last longer for the buck of fat that gets oxidized, of course compared to energy production from carbohdyrate metabolism only.

Only calories from carbohydrates are stored as fat. For a serious book, that statement is not only inaccurate but misleading. Calories are not stored, no matter what seemingly authoritative people say. Excess carbohydrates fuel fat synthesis, so what is actually stored is fat, pure and simple. Stored carbohydrate (found mainly in muscle and liver) has a name and it is glycogen. The misuse of terms is one of the reasons we're having this discussion.


So, what I'm looking for is a detailed description, from an authoritative source, that will either support or refute the argument.


Sorry I wasn't authoritative enough for you. Rather than an 'authoritative' source, you might want to get the biochemistry facts straight. At times, it seems to me that you're making a literal interpretation of certan facts without considering the background. The quote from your other post is an example of that.

When I read your story, which I thank you for sharing, I thought... 'why didn't he start by explaining all this instead of trying to find shortcuts?' From what you shared, you've been all over trying this and that. I actually wonder how much do you understand of Protein Power. When I started to follow this plan in 1999, I didn't belive a word of it and it's my job to know biochemistry and metabolism! What they wrote sounded so ridiculous and counterintuitive that I decided that I would follow the plan to the letter just to prove them wrong. As a scientist, I'm not comfortable with variables I can't control, so following the plan to the letter would make sure I wasn't the uncontrollable variable and nobody would say 'ah, you didn't do it the way it is supposed to...' Needless to say that I was also looking for something that would bring my cholesterol down, and triglycerides, blood pressure, blood sugar and of course body weight. Nonetheless, I set out to find the flaw in their reasoning. Today, good 50 lbs less, I'm still looking for that flaw. I've researched this plan from the inside out, from top to bottom and I've been able to follow it even under circumstances that were completely adverse. I do have the list of references of The Protein Power LifePlan should you care to review them as well. If there is anything I can say about this plan, is that its principles can be explained based on what it is known about our physiology, the science is not just sound but solid and the results reproducible and sometimes even predictable. The same science is behind the ever increasing amount of studies being published with respect to the benefits of carboydrate control as well as the benefits of an adequate amount of dietary protein (not what's currently recommended).

Your current situation may be result of something completely different that has nothing to do with this discussion. If you're interested in learning more about this and also give it another try to your weight loss, I'm sure we can help you and support you in your effort. One thing many here realize is that there is much to be 'unlearned' before they can even make a dicisive change in their life style.

[Gaelen]

That's a snotty answer, but it still deserves a response.

Mike, it wasn't intended as a snotty answer. It was intended to get you to do exactly what you did--share your story and elaborate on what you're looking for. Everyone might have been able to give you more pertinent responses if you'd led with that information.

For instance, there's an entire section at the front of these forums called "Getting Started." In it is a forum of links and information about PP which includes .pdfs of at least a dozen published articles that explain the science, authoritatively, as well as a link to a complete scientific bibliography for Protein Power Lifeplan. There is a link to www.nutritionandmetabolism.com where you will find literally 100s of articles that will correct the misconceptions about the biochemistry of nutrition. If you're looking to demonstrate to a doctor that effective low carbing is not all about calories, there is a link to a couple of articles which describe the thermodynamics of nutrition, and the false hypothesis of the old 'a calorie is a calorie' argument. I think it's pretty easy to find that stuff, and it's one of the most viewed areas of this site. The items included in those forums answer a lot of questions...but they're only useful if you check them out.

So investigate those links, and if you still have questions about low-carbing that you can't explain to your doctor, we're right here. However, be aware that dietary misinformation and prejudices are often not easy to de-trench, even when confronted by hard science that indicates they're faulty. YMMV.

[meburke]

Outstanding! Thank you both for responding. I obviously rushed the forums and missed the articles Gaelen mentioned, and Gabriel is right: I don't know enough about the biochemistry and am (was) in a hurry to learn. I rushed right to "Science" instead of exploring the rest of the forums. (Gaelen's directions to the articles should be included as a sticky at the top of this forum.) And, a good part of the confusion is because my memory of what I read so many years ago is not complete and coherent, and I was not clear in expressing the distinctions between what I thought I read and what I needed to know. I just ordered $160 worth of Biochemistry and Physiology books. I guess I'll add the "Protein Power Life Plan" and then I'll have the references Gaelen mentioned.

Gabriel's post alone pretty much supports the argument up to a point, but I still need to construct my own understanding based on the research I've unearthed and the links Gaelen provided.

And, I have not actually followed the program precisely. I generally keep my carbs somewhere between 75-125 per day, with an occasional splurge and a set birthday party on the last Wednesday of the month put on by a club I belong to. (Actually, that's where I dose up on ice cream and cake once a month.) So, it's no wonder I haven't actually lost any weight, but changing from a low-fat to a reduced-carb diet made an immediate change in my energy level and keeps my numbers in the right range.

Now I've made the commitment to get fit and lean, so I suspect that this is going to require more discipline and less indulgence.

I think I've got the sources for my discussion with my doctor now. Thank you for the help.

Mike

[Gabriel Guzman]

I'm not sure I supported the argument that dietary fat doesn't get stored, or that carbohydrates are the only nutrient that get stored as fat... If anything, I said the opposite!

If you want to review topics in biochemistry and metabolism, and if you haven't yet spent that money in books, these are three books that I'd suggest you to consider:

Lehninger Principles of Biochemistry (http://www.worthpublishers.com/lehninger/) (Wroth Publishers). The Fourth Edition (the latest one) costs about $146 new, but it can be found for half that price used (don't always need a new book if you can find a better alternative that is still in good condition).

Metabolism at a Glance (http://www.amazon.com/Metabolism-Glance-At-Blackwell/dp/0632052740) by J.G. Salway (Blackwell Science). There is a Third Ed. out now (~$37 new or ~$16 used).

Medical Biochemistry (http://www.blackwellpublishing.com/book.asp?ref=9781405113229), also by J.G. Salway (~$30 new).

Lehninger is an enjoyable book; goes into topics in great depth, has problems (great for teaching), nicely illustrated and just an all-around well written book. Although Lehninger is my favorite, there are others famous biochemistry textbooks currently used in College and Universities that may be less expensive.

The other two are also great books for, like the name suggests, at a glance review of topics in biochemistry and metabolism. J.G. Salways writes clearly, the illustrations are outstanding and not complicated and, for their price, they're real treasures.

Beware that must metabolism and biochemistry books still adhere somewhat to the old thinking that dietary carbohydrates are essential for life, which are not, and may still refer to studies that propose the lipid hypothesis as the cause of heart disease, obesity and metabolic syndrome, which is not been proved yet and doesn't look like it's ever going to be.

[Reverie]

Mike: it would be interesting if you could read PPLP and get serious about hitting the plan starting with intervention (<=40g carbs daily). See if it clears up your muscle stiffness as well as help you lose weight. High insulin levels are very damaging. You might also try some good fish oil to reduce inflammation if you are not already doing that. I also like glucosamine/chondroitin for joint stiffness.

This was a good discussion. I had the same question about whether dietary fat was stored as fat. When reading many low carb books, they make it seem like you can eat as much fat as you want as long as you keep carbs low. But in PPLP, you will find a page that explains if you are following the plan and still not losing weight, you may be eating too much fat.

I had found this about fat metabolism:
http://www.unisanet.unisa.edu.au/08366/h&p2fat.htm

[LisaS]

Lehninger Principles of Biochemistry (http://www.worthpublishers.com/lehninger/) (Wroth Publishers). The Fourth Edition (the latest one) costs about $146 new, but it can be found for half that price used (don't always need a new book if you can find a better alternative that is still in good condition).


what, not Stryer's? :) Either one makes a great weight for the backpack when not being read.

If you want a ugrad level overall Physiology book, Vander's Human Physiology is a pretty read. Guyton & Hall's Medical Physiology is also good if you want a little more depth in physiology.

These should all be available in any good University Library - and many public universities have a policy where you can get a library card if you live in the community w/out needing to be a student.

[meburke]

Gabriel: True, you didn't specifically support the argument. However, in reading your posts, you were consistent with the requirement that a quantity of carbohydrates need to be ingested in order for the ketones to be converted, else they are excreted.

It is apparent to me that the book "Protein Power" isn't complete enough for me, and I need to buy the PPLP book now tht I've committed to losing the weight.

Lisa: I think your signature with the countdown milestones is great! I'm going to have to do that, too! What a great way to keep your objectives visible!

I appreciate the support.

Mike

[meburke]

Gabriel: The Lipid Hypothesis gave me fits when I originally wanted to change from the low-fat diet (as proposed by Dean Ornish) in favor of the low-carb diet. Obviously, TLH is the party line, and I will probably have to argue its merits with my doctor at some point, but I think I'm just going to show results in the short term instead trying to make an intellectual case.

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2073909&dopt=Abstract

Mike

[Gabriel Guzman]

Gabriel: True, you didn't specifically support the argument. However, in reading your posts, you were consistent with the requirement that a quantity of carbohydrates need to be ingested in order for the ketones to be converted, else they are excreted.
Mike

Not really, only if ketones are to be used completely, and that makes all the difference and doesn't meant that dietary carbohydrates are essential either. There is no strict requirement to use all the ketones that are produced and as the body gets more adapted and more efficient, even the production of ketones is adjusted to the energy demand. In other words, your body doesn't have to use all the ketones you produce, but you can be sure that if carbohydrates are restricted, then ketones will meet the energy demand.

[lyn64]

Can't free fatty acids in the blood (ie. absorbed in the digestive tract) also be used to provide energy directly by cells which have mitochondria (all except a few kidney cells and some in the CNS)? So fat in the blood can be an energy source without even needing to go through the intermediary step of being converted to ketones in the liver?

I believe that this direct burning of FFA's in cell mitochondria (ie. not the Krebs cycle?) becomes increasingly efficient the longer a person spends on a restricted carbohydrate diet. Gabriel? So being in 'ketosis' (apart from producing a few ketones for the few cells that can't FFA's directly)after many years on very low carb diet, is not very appropriate terminology. 'Lipolysis would perhaps be more so. I can never understand why sports tragics refer to VL carb diets as necessarily 'ketogenic' when after many years on VLC, you would hardly be making or using any ketones at all.


Lyn

[LisaS]

as I recall, beta-oxidation breaks down fatty acids into acetyl-CoA (well, many of them). These acetyl-CoA can then enter Krebs directly or be converted into ketones (in the liver) so rather than "not the Krebs cycle" I'd say "via the Krebs cycle" - this is what we commonly call fat burning - especially in skeletal muscle. The FADH2 and NADH produced during beta-oxidation are used to produce ATP, but the great majority of the energy from fat oxidation is via the acetyl-CoA entering the Krebs cycle & subsequent ETS. I think you get something like 14 ATP per turn of beta-oxidation, and 10 of those are from oxidizing the Acetyl-CoA produced.

Even so, ketone bodies are just a tricky way of transporting acetyl-CoA in the blood as ketones are water soluble. Once these arrive at the target cells, the synthesis process is reversed to yield acetyl-CoA to enter the Krebs cycle to be oxidized. So it all comes to the same end - assuming the ketones reach a destination cell and are not excreted first (acetone is always excreted as it cannot become acetyl-CoA again, at least not in humans).

or at least that's the way I remember it - open to correction of course - its been a couple of years since I took this stuff.

now, as far as I know, if TAGs are taken up by cells, they would be ripe for the picking for TAG-to-glycerol + 3FFA conversion, just as stored TAGs would be - I assume that is what you meant by direct use in the cells rather than as ketone bodies. This would make more sense for the cell, as it would get the benefit of the electron receptors from beta-oxidation as well as the acetyl-CoA(s) - and it would be less work for the liver, which has enough other jobs :)

I think you are on the right track in that once your fat metabolism enzymes are up-regulated, you'd be burning most of the fat right it in the cell, except for those that prefer ketones. The ketones your liver would be producing for you would be those sufficient for ketone-dependent and/or ketone preferring cells. Whether these would be at levels sufficient to be detected as "in ketosis" - I have no idea, but maybe Gabe does. I would think that continued minimal carb consumption would be suffient to keep detectable ketones in the bloodstream, even long term - but that's just speculation on my part.

[Gabriel Guzman]

Can't free fatty acids in the blood (ie. absorbed in the digestive tract) also be used to provide energy directly by cells which have mitochondria (all except a few kidney cells and some in the CNS)? So fat in the blood can be an energy source without even needing to go through the intermediary step of being converted to ketones in the liver?

Indeed they do, but the only way to produce energy using fatty acids is through the Krebs Cycle and the only way to enter the cycle is either by becoming Acetyl CoA, that's the ticket. Tissues that can use ketone bodies have the necessary enzymes that can convert ketones into Acetyl CoA. Muscles can use fatty acids and ketone bodies.


I believe that this direct burning of FFA's in cell mitochondria (ie. not the Krebs cycle?) becomes increasingly efficient the longer a person spends on a restricted carbohydrate diet.


The Krebs cycle takes place inside the mitochondrion. That's why cells that don't have mitochondria can't use fatty acids to produce energy. Think of the white muscle fibers, for example, which are anaerobic, compared to red fibers, which are aerobic and are rich in mitochondria.


Gabriel? So being in 'ketosis' (apart from producing a few ketones for the few cells that can't FFA's directly)after many years on very low carb diet, is not very appropriate terminology.


It's the other way around. Only few tissues can't use ketones to produce energy. Most tissues can, including the brain which actually swithces quickly to the use of ketones for energy. Ketosis only means the 'regulated production of ketone bodies' and the amount of ketones depends on the supply of fatty acids.


'Lipolysis would perhaps be more so. I can never understand why sports tragics refer to VL carb diets as necessarily 'ketogenic' when after many years on VLC, you would hardly be making or using any ketones at all.


Lipolysis is the breakdown of triglycerides into free fatty acids, which occurs in adipose tissue. I understand your confusion with respect to the term 'ketogenic'. In my opinion is misused. Nonetheless, you never stop using ketones, ever. If you haven't had anything to eat for hours before you sat down to read this post, your body is already producing ketones according to your individual energy demand. How much or how little depends on your own demand, but they are being produced. Every time fat gets the call to be used for energy production, triglycerides are broken down into fatty acids and transported where they're needed. They enter the mitochondria (through what is known as the Carnitine shuttle), where they are beta-oxidized to produced Acetyl CoA and ketone bodies ketone bodies.

What is important to understand is what happens when carbohydrates are restricted. Since there is no other source of glucose to maintain blood levels, the liver makes it by gluconeogenesis. Oxaloacetate, an important intermediate of the Krebs cycle is continuously being directed away from the mitochodrion to the cytosol for gluconeogenesis. This is also coupled with constant supply of glycerol from beta oxidation of fatty acids. Now, oxaloacetate is needed in the Krebs cycle so Acetyl CoA can enter; when oxaloacetate and Acetyl CoA combine, they form citrate (that's how Acetyl CoA enters the cycle). Under these circumstances, the increased flux of Acetyl CoA being produced from beta-oxidation is used by a specialized enzyme, which converts Acetyl CoA into acetoacetyl CoA, a precursor of ketogenesis. Two more specialized enzymatic reactions will make acetoacetate and D-3-hydorxybutyrate, the two acids known as 'ketones'.

What adaptation to a restricted or controlled carbohyrate diet does is optimize the production and utilization of ketones. To me, this regulation is just fascinating; the rate of ketone production is coupled to the supply of fatty acids and the regulation of beta-oxidation. The metabolic scenario is ultimately what determines if beta-oxidation is favoured over carbohyrate metabolism for energy production.