12

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Metabolic difference between fasting and 100% fat?

Answered on August 19, 2014
Created November 10, 2010 at 6:10 PM

The title pretty much sums up my question. What are the metabolic differences, if any, between fasting and eating 100% fat?

I'm not clear that there are any, so I am very curious to hear what others think. No carbs/protein means gluconeogenesis and ketosis will be in full force and blood glucose will be low. Fat mobilization is still going to be in effect as far as I can tell, the dietary fat would just be topping up adipose tissue.

Anything I'm missing?

Update Dec 10: no one has pointed out a metabolic difference yet, but Eva pointed out that the digestion of fat could itself involve various signaling pathways. Does anyone know details about digestion of a 100% fat meal? Have any studies been done on this?

D31a2a2d43191b15ca4a1c7ec7d03038

(4134)

on March 04, 2012
at 12:43 AM

... As the glycerol is nearly ten percent of triglyceride by weight and two molecules of glycerol combine to form one molecule of glucose, this also supplies a source of glucose.

D31a2a2d43191b15ca4a1c7ec7d03038

(4134)

on March 04, 2012
at 12:42 AM

Dietary proteins are converted to glucose at about fifty-eight percent efficiency, so approximately 100g of protein can produce 58g of glucose via gluconeogenesis.[v] During prolonged fasting, glycerol released from the breakdown of triglycerides in body fat may account for nearly twenty percent of gluconeogenesis.[vi] Body fats are stored as triglycerides, molecules that contain three fatty acids combined with glycerol. The fatty acids are used directly as a fuel, with the glycerol stripped off. This is not wasted....

D31a2a2d43191b15ca4a1c7ec7d03038

(4134)

on March 04, 2012
at 12:42 AM

Matt, Barry Groves' site, has an article by Prof. John Yudkin. He has 10% off the glycerol in fat. It's on this page: http://www.second-opinions.co.uk/fat-not-protein.html I'll put the paragraph in the next comment.

77877f762c40637911396daa19b53094

(78467)

on October 04, 2011
at 02:41 PM

Sienna, you are just plain wrong! Especially in the cases of severely obese. The easiest source of energy is stored body fat. It only breaks down a small amount of muscle tissue to create a very small amount of sugar. And the internal organs are the last to go. If you have 10% body fat, then this is an issue. Most people do not have that problem in our modern society...

B8592e62f9804ddabae73c1103d6bcb9

(1956)

on December 23, 2010
at 12:43 PM

... which would be fairly low anyway by this point, as ketosis spares glucose for the few parts of the body that can only run on glucose. Muscle and Fat tissues tend to be lost at about equal weights when starving.

B8592e62f9804ddabae73c1103d6bcb9

(1956)

on December 23, 2010
at 12:38 PM

The body doesn't go straight for the muscle tissue when you stop eating, first blood glucose it maintained from glycogen stored in the liver. Everyone seems to forget about this. It only lasts about 24 hours though. If muscle was that first thing your body went for, no-one would ever lose any fat. Fat will provide some sugar via glycerol. 'Lean' muscle is actually very fatty and will provide the same a ratio of protein and fat calories to supply most calories as fat, and fairly high-protein so some can be turned into the glucose required by the body...

Bdcb2101fd3f1853cfd645094d8ad086

on December 08, 2010
at 04:55 PM

I am not convinced that there is "no insulin response to dietary fat." I have read that there is always an insulin response to calories consumed. Can anyone clarify this?

D67e7b481854b02110d5a5b21d6789b1

(4111)

on November 11, 2010
at 07:11 PM

This is a great question, and I am so curious to see what the consensus will be.

Cb2415c2aef964ab499a09dc92ae7e01

(783)

on November 11, 2010
at 03:54 PM

Part II - I don't know the issue behind your question. If you are trying to lean out, then try 1 week of a breakfast of 500-800 cals straight coconut oil (yuck) and one week skipping breakfast entirely. See what works better.

Cb2415c2aef964ab499a09dc92ae7e01

(783)

on November 11, 2010
at 03:53 PM

I'm not a biochemist so don't know the signaling mechanism. From common sense perspective, I'd say because there is no fuel in the tank. How does the body 'know' to combat illness when infected with virus? It just does. How does body 'know' to get energy out of stored tissue when there is no food coming in? It just does. But your question seems a bit circular - the process of getting energy from muscle and fat *is* autophagy.

F8fa4b0809d3b74fcf0361c0d53b60c1

(911)

on November 11, 2010
at 09:29 AM

Your point about digestion is the first thing that has given me pause thus far. The presence of fat in the gut seems very likely to produce SOME form of chemical messaging. That could very well be altering the function of the body - but what signaling pathways are activated by a PURE fat meal? Maybe just pathways required to bring the fat to adipose tissue, but maybe it also influences energy signaling somewhere... I wonder if responses to 100% fat meals has ever been studied?

F8fa4b0809d3b74fcf0361c0d53b60c1

(911)

on November 11, 2010
at 09:26 AM

Yes, but the different hormonal responses to carbs/fat/protein are vitally important to understanding their impact on the body. You make the same point I did in the original post, that dietary fat goes into adipose tissue and is then mobilized from there, which makes it equivalent to fasting.

F8fa4b0809d3b74fcf0361c0d53b60c1

(911)

on November 11, 2010
at 09:22 AM

I also like to think about the role of ketosis in human metabolism, and it does seem to me like ketosis is to some degree the default metabolic state. This doesn't address the question however. Those posts from Peter on high-fat mimicking fasting would be much appreciated, I can't locate them myself right now.

F8fa4b0809d3b74fcf0361c0d53b60c1

(911)

on November 11, 2010
at 09:19 AM

That was an argument about the definition of the word "fast." This is a question about whether the metabolic state thus induced in each case is identical.

F8fa4b0809d3b74fcf0361c0d53b60c1

(911)

on November 11, 2010
at 08:50 AM

But what is the signaling mechanism for autophagy? How do the cells "know" that energy is low? Because after all, they're actually getting a steady supply of energy... from muscle and fat tissue. I would suspect beta-hydroxybutyrate, one of the ketone bodies, in which case, fasting=100% fat. Presumably someone has researched this...?

4e40d2b9e1a762949a25b958762aa10d

(762)

on November 10, 2010
at 09:30 PM

Hi Sienna, Perhaps I misunderstand you, but I don't believe most anorexics are clinically obese. To be diagnosed as anorexic one must, along with other psychological criteria, be lighter than 85% of that person's peers. Perhaps you meant that anorexics can be overfat because they have so little body tissue? Mike

D30ff86ad2c1f3b43b99aed213bcf461

on November 10, 2010
at 08:25 PM

I'm still wondering about this. A paleohacks thread from a while back asked if heavy whipping cream "ends" a fast, but it looks as though opinions were mixed: http://paleohacks.com/questions/3269/does-drinking-heavy-cream-end-a-fast#axzz14ug3mbeV

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6 Answers

4
D31a2a2d43191b15ca4a1c7ec7d03038

on November 10, 2010
at 08:45 PM

If I can find the post or comments Peter Dobromylskyj has made at his blog, Hyperlipid, about high fat mimicking fasting, I will post them, with the links. Also, there might be something in the Stefansson, Pennington, Kekwick, Donaldson, MacKarness realm on high fat diets being similar to fasting. If I can find references, I will post those, too.

Meanwhile, I hope this is of some use:

Dr. Kurt Harris, in this post, the last paragraph, emphasis added:

http://www.paleonu.com/panu-weblog/2009/8/27/can-protein-turn-into-fat.html

As far as raising your insulin levels, glucose has the biggest effect, and fructose is bad because it induces insulin resistance, which requires you to produce higher levels of insulin to handle the same amount of glucose. Protein requires insulin but less than glucose and there is some insulin response to dietary protein. There is no insulin response to dietary fat. All three require some basal insulin for normal metabolism.


Here is something Stan Bleszynski posted, related to this subject, at his blog:

http://stan-heretic.blogspot.com/2008/08/snacking-and-glucoseketogenic-cycling.html

Snacking and glucose/ketogenic cycling

This is a theory, very speculative. I came to think about it, inspired after reading the latest articles by Peter (Hyperlipid blog, see also his Kitava articles). I am thinking about the effect of frequent snacking in between the meals on a high carb diet, may be more damaging than we thought. Under a healthy metabolism, even on a high carb diet, one's body goes back to ketogenic state some time after every meal, when most body tissues revert back to using lipids and ketone bodies as fuel. This should happen in between the meals providing that the body is given enough time to burn glucose off and to switch. On the other hand, any time one eats something sugary or starchy in between the meals, insulin inrush causes the body to switch back to glucose processing state, turning off production of ketone bodies and turns off the release of adipose fat into bloodstream. It takes about 1-2 hours to work out all that insulin peak. Probably longer for older people.

For some reason, our bodies probably require this alternating between glucose-burning/ketogenic cycles to be done throughout the day to work properly. This is based upon the assumption that ketogenic mode is essential for the body and must take place at least some of the time throughout the day, every day. I suspect that frequent snacking on a high carbohydrate diet derails that cycling and may be one of main triggering factors behind the development of the metabolic syndrome.

From my personal observation, one can notice that people who are used to snack frequently are often obese and often have metabolic syndrome. Perhaps there is a causual connection? Perhaps it is not just what and how much one eats but how often and when?

Diets based on natural whole food like our vegetarian friends recommend, usually discourage sugary or starchy snacks, or discourage consumption of the processed food that forms the typical fast food snacks. It makes snacking more difficult, especially that preparation of meals out of natural unprocessed whole food is time consuming and labor intensive. Perhaps that may be one of the reason why such whole food natural diets are often helpful?

Of course, the high fat low carb diets make that issue irrelevent since a high fat snack would not cause the glucose+insulin spike thus would not break the ketogenic mode. This could be another reason why the high fat low carb diets work so well!

F8fa4b0809d3b74fcf0361c0d53b60c1

(911)

on November 11, 2010
at 09:22 AM

I also like to think about the role of ketosis in human metabolism, and it does seem to me like ketosis is to some degree the default metabolic state. This doesn't address the question however. Those posts from Peter on high-fat mimicking fasting would be much appreciated, I can't locate them myself right now.

Bdcb2101fd3f1853cfd645094d8ad086

on December 08, 2010
at 04:55 PM

I am not convinced that there is "no insulin response to dietary fat." I have read that there is always an insulin response to calories consumed. Can anyone clarify this?

D31a2a2d43191b15ca4a1c7ec7d03038

(4134)

on March 04, 2012
at 12:42 AM

Dietary proteins are converted to glucose at about fifty-eight percent efficiency, so approximately 100g of protein can produce 58g of glucose via gluconeogenesis.[v] During prolonged fasting, glycerol released from the breakdown of triglycerides in body fat may account for nearly twenty percent of gluconeogenesis.[vi] Body fats are stored as triglycerides, molecules that contain three fatty acids combined with glycerol. The fatty acids are used directly as a fuel, with the glycerol stripped off. This is not wasted....

D31a2a2d43191b15ca4a1c7ec7d03038

(4134)

on March 04, 2012
at 12:43 AM

... As the glycerol is nearly ten percent of triglyceride by weight and two molecules of glycerol combine to form one molecule of glucose, this also supplies a source of glucose.

D31a2a2d43191b15ca4a1c7ec7d03038

(4134)

on March 04, 2012
at 12:42 AM

Matt, Barry Groves' site, has an article by Prof. John Yudkin. He has 10% off the glycerol in fat. It's on this page: http://www.second-opinions.co.uk/fat-not-protein.html I'll put the paragraph in the next comment.

3
Cb2415c2aef964ab499a09dc92ae7e01

(783)

on November 10, 2010
at 11:26 PM

Fasting isn't just a matter of keeping insulin low. It is giving the body a break from digesting, period - stomach, pancreas, intestines. This allows autophagy to occur.

"Art DeVany on autophagy - Art Devany discusses how fasting - being hungry - can promote autophagy (literally self-eating) a process in which your cells consume and recycle damaged internal material.

The process seems to be triggered when the energy content of the cell declines so that the cell literally consumes itself. It goes after the damaged materials first, so there is a strong link between repair of damaged tissues and fasting or low energy state in the cell. So, it you are over-fed you down regulate cellular repair. You want to go hungy episodically to turn on cellular autophagy and repair those damaged tissues."

If you are going to fast, fast; if eating, eat. Why muck around with 100% fat which would be unsatisfying for more than a snack.

Cb2415c2aef964ab499a09dc92ae7e01

(783)

on November 11, 2010
at 03:54 PM

Part II - I don't know the issue behind your question. If you are trying to lean out, then try 1 week of a breakfast of 500-800 cals straight coconut oil (yuck) and one week skipping breakfast entirely. See what works better.

Cb2415c2aef964ab499a09dc92ae7e01

(783)

on November 11, 2010
at 03:53 PM

I'm not a biochemist so don't know the signaling mechanism. From common sense perspective, I'd say because there is no fuel in the tank. How does the body 'know' to combat illness when infected with virus? It just does. How does body 'know' to get energy out of stored tissue when there is no food coming in? It just does. But your question seems a bit circular - the process of getting energy from muscle and fat *is* autophagy.

F8fa4b0809d3b74fcf0361c0d53b60c1

(911)

on November 11, 2010
at 08:50 AM

But what is the signaling mechanism for autophagy? How do the cells "know" that energy is low? Because after all, they're actually getting a steady supply of energy... from muscle and fat tissue. I would suspect beta-hydroxybutyrate, one of the ketone bodies, in which case, fasting=100% fat. Presumably someone has researched this...?

1
62ed65f3596aa2f62fa1d58a0c09f8c3

(20807)

on November 11, 2010
at 05:56 AM

An interesting story: Long ago, doctors noticed that some epileptics did not have seizures during times of starvation. Thus starvation was considered a short term treatment technique for those suffering seizures. This observation goes back so far that it was even written about in the Bible. But the obvious drawback is you can't stay on such a treatment long term and still be alive.

In the 20s, smart doctors reasoned that a high fat diet might accomplish similar effects to starvation, ie ketosis. And it worked. Ketosis can eliminate seizures in 50% or more of siezure patients, similar to fasting/starvation. Metabolically, they are very similar.

But one obvious difference is you can maintain weight on the fat eating diet. Energy comes from the fat you eat instead of the fat on your butt! ;-) Other obvious diffs, when eating, you will need to funnel a lot of energy to digestion. Whereas in fasting, you may trigger some kinds of alertness and food gathering instincts and hormones. You may also have to deal with any side effects of fat leaving the fat cells includng (if such is really what happens) potential release of stored toxins.

F8fa4b0809d3b74fcf0361c0d53b60c1

(911)

on November 11, 2010
at 09:29 AM

Your point about digestion is the first thing that has given me pause thus far. The presence of fat in the gut seems very likely to produce SOME form of chemical messaging. That could very well be altering the function of the body - but what signaling pathways are activated by a PURE fat meal? Maybe just pathways required to bring the fat to adipose tissue, but maybe it also influences energy signaling somewhere... I wonder if responses to 100% fat meals has ever been studied?

1
77877f762c40637911396daa19b53094

(78467)

on November 10, 2010
at 09:46 PM

can't imagine what one can be on 100% fat for - but that's perhaps due to lack of imagination

on a side note, as far as i can tell from reading the blog "carbsanity.blogspot.com", you can't "run on" dietary fat directly - at first, all consumed lipids get incorporated into adipose / muscle tissue, and released (as 'your own fat') only in an "on-demand" mode during time of negative energy balance, thus being an ideal "fat storage" fuel: carbs or protein require at least some energy to be converted into adiposity - that shattered my personal long-standing fat-centric paradigm! - before i knew the "truth" (=eat fat, a lot of fat, mostly fat) but now i'm in the "darkness"

F8fa4b0809d3b74fcf0361c0d53b60c1

(911)

on November 11, 2010
at 09:26 AM

Yes, but the different hormonal responses to carbs/fat/protein are vitally important to understanding their impact on the body. You make the same point I did in the original post, that dietary fat goes into adipose tissue and is then mobilized from there, which makes it equivalent to fasting.

1
4e40d2b9e1a762949a25b958762aa10d

(762)

on November 10, 2010
at 08:05 PM

Hi Will,

You ask a very good question. To make sure I understand, what do you mean by metabolic differences? For this response, I will assume you mean blood lipids and glucose.

Before addressing your question, you should note that in a metabolically normal person (although this definition may be circular), blood sugar will stay between 80-120 mg/dl despite fasting. Your question anticipates this because increased gluconeogenesis partially compensates for decreased dietary intake (increases glucose supply) and ketosis lessens the body's demand for glucose (decreases glucose demand).

Although I hypothesize that eating more increases insulin secretion, I cannot find supporting data. The studies I found through PubMed and Google Scholar all require one to extrapolate beyond the scope of the study. For example say decreasing carbs from 30% to 10% causes a decrease in fasting insulin levels. Given human physiology's complexity (nonlinear responses, counter-regulatory mechanisms to maintain homeostasis), this observation does not tell us anything about what cutting carbs from 10% to 0% would do.

However, Peter at Hyperlipid details how different types of fat have unique effects on plasma lipids (triglycerides, chlyomicrons, etc).

Studying how the body reacts to a pure fat diet may unearth metabolic processes we didn't know about. However, since that is an extreme situation I am unsure how to reason to it or from it.

0
9f8111d9ecaa64ea098a0860b47300e0

on November 10, 2010
at 09:10 PM

Nope. When the body senses starvation it goes to the easiest source of energy ... protein aka lean body mass which includes the heart muscle. Protein is easily converted BY THE BODY OVER to sugars for energy. This is why most anorexics are clinically obese because all the lean tissue has been scavenged. Hope I am remembering this correctly from my PT days. HTH, ~S

4e40d2b9e1a762949a25b958762aa10d

(762)

on November 10, 2010
at 09:30 PM

Hi Sienna, Perhaps I misunderstand you, but I don't believe most anorexics are clinically obese. To be diagnosed as anorexic one must, along with other psychological criteria, be lighter than 85% of that person's peers. Perhaps you meant that anorexics can be overfat because they have so little body tissue? Mike

B8592e62f9804ddabae73c1103d6bcb9

(1956)

on December 23, 2010
at 12:43 PM

... which would be fairly low anyway by this point, as ketosis spares glucose for the few parts of the body that can only run on glucose. Muscle and Fat tissues tend to be lost at about equal weights when starving.

B8592e62f9804ddabae73c1103d6bcb9

(1956)

on December 23, 2010
at 12:38 PM

The body doesn't go straight for the muscle tissue when you stop eating, first blood glucose it maintained from glycogen stored in the liver. Everyone seems to forget about this. It only lasts about 24 hours though. If muscle was that first thing your body went for, no-one would ever lose any fat. Fat will provide some sugar via glycerol. 'Lean' muscle is actually very fatty and will provide the same a ratio of protein and fat calories to supply most calories as fat, and fairly high-protein so some can be turned into the glucose required by the body...

77877f762c40637911396daa19b53094

(78467)

on October 04, 2011
at 02:41 PM

Sienna, you are just plain wrong! Especially in the cases of severely obese. The easiest source of energy is stored body fat. It only breaks down a small amount of muscle tissue to create a very small amount of sugar. And the internal organs are the last to go. If you have 10% body fat, then this is an issue. Most people do not have that problem in our modern society...

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