Fasting and Muscle Mass – Fasting Part 15

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It seems that there are always concerns about loss of muscle mass during fasting. I never get away from this question. No matter how many times I answer it, somebody always asks, “Doesn’t fasting burn your muscle?”

Let me say straight up, NO.

Here’s the most important thing to remember.  If you are concerned about losing weight and reversing T2D, then worry about insulin. Fasting and LCHF will help you. If you are worried about muscle mass, then exercise – especially resistance exercises. OK? Don’t confuse the two issues. We always confuse the two issues because the calorie enthusiast have intertwined them in our minds like hamburgers and french fries.

Weight loss and gain is mostly a function of DIET. You can’t exercise your way out of a dietary problem. Remember the story of Peter Attia? A highly intelligent doctor and elite level distance swimmer, he found himself on the heavy end of the scale, and it was not muscle. He was overweight despite exercising 3-4 hours a day. Why? Because muscle is about exercise, and fat is about diet. You can’t out-run a bad diet.

Muscle gain/ loss is mostly a function of EXERCISE. You can’t eat your way to more muscle. Supplement companies, of course, try to convince you otherwise. Eat creatine (or protein shakes, or eye of newt) and you will build muscle. That’s stupid. There’s one good way to build muscle – exercise. So if you are worried about muscle loss – exercise. It ain’t rocket science. Just don’t confuse the two issues of diet and exercise. Don’t worry about what your diet (or lack of diet – fasting) is doing to your muscle. Exercise builds muscle. OK? Clear?Macro oxidation

So the main question is this – if you fast for long enough, doesn’t your body start to burn muscle in excess of what it was doing previously in order to produce glucose for the body. Hell, no.

Let’s look carefully at this graph by Dr. Kevin Hall from the NIH in the book “Comparative Physiology of Fasting, Starvation, and Food Limitation”. Great title guys. Amazon probably couldn’t keep enough stock on the shelves.

But anywho, this is a graph of where the energy to power our bodies comes from, from the start of fasting. At time zero, you can see that there is a mix of energy coming from carbs, fat and protein. Within the first day or so of fasting, you can see that the body initially starts by burning carbs (sugar) for energy. However, the body has limited ability to store sugar. So, after the first day, fat burning starts.

What happens to protein? Well, the amount of protein consumed goes down. There is certainly a baseline low level of protein turnover, but my point is that we do not start ramping up protein consumption. We don’t start burning muscle, we start conserving muscle.

Reviews of fasting from the mid 1980s had already noted that “Conservation of energy and protein by the body  has been demonstrated by reduced … urinary nitrogen excretion and reduced leucine flux (proteolysis). During the first 3 d of fasting, no significant changes in urinary nitrogen excretion and metabolic rate have been demonstrated”.  Leucine is an amino acid and some studies had shown increased release during fasting and other had not. In other words, physiologic studies of fasting had already concluded that protein is not ‘burnt’ for glucose.Urea

It further notes that you can get increase leucine flux with no change in urinary nitrogen excretion. This happens when amino acids are reincorporated into proteins. Researchers studied the effect of whole body protein breakdown with 7 days of fasting. Their conclusion was that “decreased whole body protein breakdown contributes significantly to the decreased nitrogen excretion observed with fasting in obese subjects”. There is a normal breakdown of muscle which is balanced by new muscle formation. This breakdown rate slows roughly 25% during fasting.

The classic studies were done by George Cahill. In a 1983 article on “Starvation” he notes that glucose requirements fall drastically during fasting as the body feeds on fatty acids and the brain feeds on ketone bodies significantly reducing the need for gluconeogenesis. Normal protein breakdown is on the order of 75 grams/day which falls to about 15 – 20 grams/day during starvation. So, suppose we go crazy and fast for 7 days and lose about 100 grams of protein. We make up for this protein loss with ease and actually, far, far exceed our needs the next time we eat.MuscleBreakdown

From Cahill’s study, you can see that the urea nitrogen excretion, which corresponds to protein breakdown, goes way, way down during fasting/ starvation. This makes sense, since protein is functional tissue and there is no point to burning useful tissue while fasting when there is plenty of fat around. So, no, you do not ‘burn’ muscle during fasting.

Triglyceride

Triglyceride

Where does the glucose comes from? Well, fat is stored as triglycerides (TG). This consists of 3 fatty acid chains attached to 1 glycerol molecule. The fatty acids are released from the TG and most of the body can use these fatty acids directly for energy.

The glycerol, goes to the liver, where it undergoes the process of gluconeogenesis and is turned into sugar. So, the parts of the body that can only use sugar have it. This is how the body is able to keep a normal blood sugar even though you are not eating sugar. It has the ability to produce it from stored fat.

Sometimes you will hear a dietician say that the brain ‘needs’ 140 grams of glucose a day to function. Yes, that may be true, but that does NOT mean that you need to EAT 140 grams of glucose a day. Your body will take the glucose it needs from your fat stores. If you decide to EAT the 140 grams instead, your body will simply leave the fat on your ass, hips, and waist. This is because the body will burn the sugar instead of the fat.ADF MuscleMass1

But let’s look at some clinical studies in the real world. In 2010, researchers looked at a group of subjects who underwent 70 days of alternate daily fasting (ADF). That is, they ate one day and fasted the next. What happened to their muscle mass?

Their fat free mass started off at 52.0 kg and ended at 51.9 kg. In other words, there was no loss of lean weight (bone, muscle etc.). There was, however, a significant amount of fat lost. So, no, you are not ‘burning muscle’, you are ‘burning fat’. This, of course, is only logical. After all, why would your body store excess energy as fat, if it meant to burn protein as soon as the chips were down? Protein is functional tissue and has many purposes other than energy storage, whereas fat is specialized for energy storage. Would it not make sense that you would use fat for energy instead of protein? Why would we think Mother Nature is some kind of crazy?

That is kind of like storing firewood for heat. But as soon as you need heat, you chop up your sofa and throw it into the fire. That is completely idiotic and that is not the way our bodies are designed to work.

How, exactly does the body retain lean tissue? This is likely related to the presence of growth hormone. In an interesting paper, researchers fasted subjects and then suppressed Growth Hormone with a drug to see what happened to muscle breakdown. In this paper, they already acknowledge that “Whole body protein decreases”. In other words, we have known for 50 years at least, that muscle breakdown decreases substantially during fasting.

By suppressing GH during fasting, there is a 50% increase in muscle break down. This is highly suggestive that growth hormone plays a large role in maintenance of lean weight during fasting. The body already has mechanisms in place during fasting to preserve lean mass and to burn fat for fuel instead of protein.

So let me lay it out as simply as I can. Fat is, at its core essence, stored food for us to ‘eat’ when there is nothing to eat. We have evolved fat stores to be used in times when there is nothing to eat. It’s not there for looks, OK? So, when there is nothing to eat (fasting), we ‘eat’ our own fat. This is natural. This is normal. This is the way we were designed.

And its not just us, but all wild animals are designed the same way. We don’t waste away our muscle while keeping all our fat stores. That would be idiotic. During fasting, hormonal changes kick in to give us more energy (increased adrenalin), keep glucose and energy stores high (burning fatty acids and ketone bodies), and keep our lean muscles and bones (growth hormone). This is normal and natural and there is nothing here to be feared.

So, I will say it here, yet again.

  1. No, fasting does not mean you burn protein for glucose. Your body will run on fat.
  2. Yes, your brain needs a certain amount of glucose to function. But no, you do not have to EAT the glucose to get it there.

Continue to Fasting Part 16 – Fasting Lowers Cholesterol

2017-09-02T11:54:12+00:00 104 Comments

About the Author:

Dr. Fung is a Toronto based kidney specialist, having graduated from the University of Toronto and finishing his medical specialty at the University of California, Los Angeles in 2001. He is the author of the bestsellers ‘The Obesity Code’ and ‘The Complete Guide to Fasting’. He has pioneered the use of therapeutic fasting for weight loss and type 2 diabetes reversal in his IDM clinic.

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104 Comments on "Fasting and Muscle Mass – Fasting Part 15"

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Drew Dahlgren
Guest

Great blog post Dr. Fung! Protein wasting with fasting is so ingrained in both the medical/nutrition as well as lay community! It makes it difficult to convince people otherwise so keep up the great work! Do you have any thoughts on the use of BCAA during fasting to promote muscle growth while following a two or three days a week strength program?

Niko Espindola
Guest

I would love to hear this as well!

Wenchypoo
Guest

5 jumbo shrimp (my favorite oxymoron)

What about MILITARY INTELLIGENCE, or POLITICAL WILL? 🙂 Hubby and I are fasting through this 3-day weekend–we started at 6 Friday night, and will end at 6 on Monday night.

Wenchypoo
Guest

By suppressing GH during fasting, there is a 50% increase in muscle break down. This is highly suggestive that growth hormone plays a large role in maintenance of lean weight during fasting.

Does the mutant MTHFR gene play at all in this? If so, how?

Zachary W.
Guest
I’m a sizable fan of the blog (in enthusiasm, not girth). I’ve neither diabetic, nor particularly unhealthy (at this point), but your blog has been a wonderful source of confirmation (and compiling) of information, much of which, I’d come across over the years in my own progress with fasting and intermittent fasting. But as I am only a lowly Dr. of humanities, a medical perspective on the same research has proven an invaluable technical resource in reminding me why I eat the way I do, in spite of the incredulous looks I get from people who eat in the conventional… Read more »
Jon
Guest

This explains a great deal.

Thank you for the insight.

Steve
Guest
Zachary: I have been casually weighlifting for decades 2-3 times per week, and have read many books which assert that fasting results in diminished muscle mass. However, in light of what Dr. Fung has written here with this post, I believe that the weightlifters’ alarm is misplaced or at least there is a different explanation for the “wasted muscle” appearance. I suspect that although there is the appearance of loss of muscle,* what is really going on is that because decreased levels of insulin causes the body to excrete large amounts of water from all cells (as we who fast… Read more »
Tyler
Guest
I’ll start by saying that I agree with Steve, on the water loss. I’ve been into strength training for a while now, and have just gotten into bodybuilding. A large part of bodybuilding is achieving the “pump” or a state of hypertrophy. Glycogen stores in the muscles are primary responsible for the storage of additional water, allowing for a “fuller look”. Higher intake of water with a combination of substances such as creatine allow for further water storage. While achieving a pump the muscle enters an engorged state in which excess blood and water are pulled to the area of… Read more »
bill
Guest

ZW:

WGAS!

Zachary W.
Guest
bill, These people might “who (might) give a s**t:” [WGAS]: Dr Fung: might like to hear that his blog is helpful to people beyond those just who are battling diabetes or extreme obesity. It is called a thank you. He might also be interested in addressing the question of fasting as regards to abnormal levels of lean muscle mass. He probably has considered this, but thus far has not addressed it, nor have I seen it really addressed well elsewhere. YOU, bill: clearly cared enough to respond with a snarky comment on a blog where people are civil and appreciative… Read more »
Tony
Guest

Amen.

johnnyv
Guest

This is of interest to me.
I have seen a paper where buffering with sodium bicarbonate and potassium chloride reduced nitrogen loss by a third in fasting subjects.
Also resistance trained people generally have more myonuclei per muscle fiber than untrained.
If the rate of muscle protein synthesis decreases due to lack of stimulus or lack of substrate the fiber will shrink but not disappear once you start eating it will refill quickly.

Good review paper here on glycogen in fasting, looks like short intense training is best while fasting.
“Post-Exercise Muscle Glycogen Repletion in the Extreme: Effect of Food Absence and Active Recovery”
http://www.jssm.org/vol3/n3/4/v3n3-4pdf.pdf

Nina
Guest

Such a great post, Jason! And you’re too funny – your exasperation is palpable! Thank you for all of the invaluable information you have on your site!

Dr.S. Vijayaraghavan
Guest

Dear Dr Jason
On target yet again. I have gone through the frustration of not being able to lose weight despite working out almost an a day six days a week for three years.
I stopped this nonsense, went on LCHF diet and HIIT ( 10 mgs twice a week) and lost 8 kilos in a month.
Proof of the pudding!!!

Valerie
Guest
“Yes, if you fast for 7 days and then eat no other protein than 5 shrimps, you are fine.” Nope. Not at all. The 15-20 grams of protein per day you cite applies to prolonged starvation (about 20 days into the fast). In the same paper from Cahill, the protein loss per day after 3-4 days of fasting is 75 grams. That would be around 300 calories per day, which fits nicely with the graph you have near the top of your post. Let me repeat: according to your own data, we should expect around 75 grams of protein lost… Read more »
Tony
Guest
“Nope. Not at all.” Perhaps you should take a little time off from your in depth fasting research and work on your manners. Maybe you have a point in what you’re trying to say. Maybe you don’t. It’s hard to tell. My brain shuts down as soon as I hear your rude and disrespectful tone. You ever hear the expression “what you are speaks so loudly, I cannot hear what you’re saying”? We know Dr. Fung’s credentials. What are yours? What makes you such an expert? What’s your background in this area? What in your background and accomplishments gives you… Read more »
Valerie
Guest
“We know Dr. Fung’s credentials. What are yours?” See, that’s the scary part. I don’t have any credentials. I’m just a layperson who happens to have read some of the fasting literature (for my own weird health issues). Yet, I can spot Dr. Fung’s mistakes a mile away. Can’t you? Do gou not see the discrepancy between the graph (250-300 calories of protein burned perday) and the text (15-20 grams of protein burned per day)? Do you actually accept that 5 shrimps could contain 100 grams of protein? As for the tone, I’m sorry it causes you such distress that… Read more »
BK
Guest
I agree with Valerie. I just finished a 7 day water-only fast. And I can tell you that you indeed lose muscle. I did a DEXA scan (gold standard for body composition) prior to, and immediately after my fast. I lost 5 lbs. of muscle and 1/2 pound of fat. I was shocked. This article makes complete sense to me. I understand it. But the body is much more complex than we realize and each person is very unique. I think the fear of losing muscle is genuine, and it does have some basis from others who have done so… Read more »
Traci
Guest
You didn’t mention what your body fat vs. lean mass percentages were before the fast but at 5’3 and 115 lbs. you’re thin to begin with. I’m only 5’0 and the last time I hit 117 lbs., I looked very thin. I speculate that in your case, your body fat was low enough that you’re body decided to preserve it so that you could feed a child if you were to become pregnant. Also, lean mass isn’t just muscle is it? It’s organs, tissue, bones, blood vessels, etc. Maybe a lb. or 2 of that muscle was actually extra stuff… Read more »
Tony
Guest
“I’m having a hard time believing that the mistakes in this post and others are all unintentional.” Statements like that are the problem. They’re rude and insulting. You’re accusing Dr. Fung of being some sort of evil, lying, conniving person going out of his way to deceive people. Yet there are many on this blog, myself included, whose life have been profoundly changed by Dr. Fung. I’ve gotten a whole new lease on life following his advice after spending years trying everyone else’s to no avail. His believe system is the only one that has actually WORKED. So when I… Read more »
JW
Guest

I’m curious as to why Dr Fung would be making intentional discrepancies..this sounds like a tin foil hat conspiracy theory. Mwahaha Dr Fung is plotting to make us …err..eat less. I’m sick and tired of the nutrition wars online with so many trying to prove others wrong. What is this an ego thing? I don’t agree with 30 bananas a day man, nor vegans or low fat promoters and so simply I don’t bother to comment on their blogs, what’s the point? If you don’t like it press the esc key.

Joe
Guest

You are seriously triggered and sound like a fanboy for this doctor.

Jonah
Guest
Tony, perhaps you should set aside your butt hurt emotions and maybe focus on the question Valerie legitimately poses. Your loyalty to Dr. Fung is noted. Now how about moving on to helping this blog be informative, (not snap your fingers saying oh no she didn’t). With all due respect Dr Fung, the chart seems to indicate a higher daily oxidation of protein than 25. We could be and likely are looking at it wrong but please acknowledge this at least. Thank you for all your dedication. Also thank you Valerie and Krisztian for speaking up. Dr. Jason Fung: You… Read more »
Dustin
Guest

Quibbling with the numbers? That’s a significant difference, which was exactly the point I thought we were proving here? Basically the chart refutes everything the article says about protein loss during a fast other than it slows. Maybe I’m confused, but now this article seemed to say x doesn’t happen… But then someone says the chart shows x… Oh, well then x doesn’t matter. Completely avoiding the issue it seems.

Elaine in Big D
Guest
Valerie, thank you very much for your comments and for sparking the little debate. I appreciate your being willing to comment on this blog since it’s where much of the fasting info is being offered. I used to fast 10 days at a time back in the early 80s. In later years (after that fasting craze kinda blew over) info came out that organs could be damaged if fasting longer than three consecutive days. I felt it did damage to my heart muscle. Doctors don’t know, you can’t ask and get any kind of sensible answer. In any case, your… Read more »
Bernard P.
Guest

According to my calculations, this post should be titled PART 15 🙂

Part 14 is here:

https://intensivedietarymanagement.com/the-fasting-advantage-part-14/

Dr. Jason Fung: Thanks. I’ve corrected it.

Esmee La Fleur
Guest

That is what I thought too. Glad I was not imagining things.

Steve
Guest

Thanks again Dr. Fung for another very informative post! Your ongoing work is greatly appreciated. I just listened to your podcast with Jimmy Moore and this latest article fills in some of the gaps for me. I hope you offer your thoughts on the use of BCAA’s as mentioned above. Since we are not eating protein on an extended fast (say 2-week fast) does the protein needed for muscle repair, and growth if we are weight training, come from the autophagy process? Thanks again!

Roger@Anne
Guest

Another really good post, Dr Fung. Thanks for laying out so clearly. Do I notice a “tad” of exasperation creeping in? ?

Dr. Jason Fung: HaHa. I don’t mind lay people asking me. However, I get doctors who have never fasted or supervised a fast telling me that I’m just ‘wrong’ and fasting breaks down muscle.

Robert
Guest

As you say, the glycerol, goes to the liver, where it undergoes the process of gluconeogenesis and is turned into sugar, which means that the liver has the ability to produce sugar from stored fat, even if you are eating zero carbs, even if you are fasting.
My question is : if you have high insulin resistance, could that liver produced sugar raise your blood sugar over the limit ?
Please clarify that point.
Thank You

Magnus Løining
Guest
Great post Dr. Fung. This subject is always an issue when it comes to fasting, and many are arfraid because of it. You really succeed with the way you present it here, and make it understandable for people. This shows that our biology is way more complex than just “you must eat all the time to have enough energy”. We are complex machines that are able to store energy for later use, and produce our own energy from our storage, without “breaking down” the body, which make perfekt sense. How would we survive our evolution if we didnt have this… Read more »
Vicente
Guest

Hi Jason,
I don’t think our brain needs so much glucose (” the brain ‘needs’ 140 grams of glucose”).

Have a look at Figures 1 and 3 on this article (pages #7 and #9). Read, please, the text under Fig 3.

Thanks for your work.

Dr Jason Fung: I agree that the brain likely could get by with less. However, this 140 grams number gets bandied around a lot by dieticians, which is the reason I used it.

MachineGhost
Guest

Not sure where 140 came from, but the IOM set the RDA for carbohydrates at 130g.

Krisztián Pintér
Guest

the article says 15-20g protein per day, however the diagram says 250kcal/day from protein. these numbers are at odds with each other. 250kcal comes from over 80g. how do you reconcile?

Sylvain M
Guest
Dr Fung, thank you for helping us better understand our metabolism. Today, I am not sure to understand your point properly. At first sight, it seems that you are suggesting that, all the weight loss, of a person loosing let’s say 50 pounds on a 100 days fast will “only” come from body fat and water? Wich would be about 454 (g) / 2 = 227 (g) per day. On the other hand refering to approximate data from the graph at the beginning, on day one an fifteen, I think that you are saying that, more or less 250kcal or… Read more »
Jane
Guest
Dear Dr. Fung, I am still working on understanding. What if someone has been very inactive for quite a while? If so, and one is insulin resistant, Is it necessary to engage in some form of strength training to retain our lean mass while fasting? In order to To rebuild lean mass as a matter of course during the daily protein turnover process, instead of losing it? Or, if not “strength training,” then at least moving around more? If lean mass is protected by growth hormone, what about older folk, such as those over 60 years old? Don’t they have… Read more »
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Wenchypoo
Guest
From Cahill’s study, you can see that the urea nitrogen excretion, which corresponds to protein breakdown, goes way, way down during fasting/ starvation. This makes sense, since protein is functional tissue and there is no point to burning useful tissue while fasting when there is plenty of fat around. So, no, you do not ‘burn’ muscle during fasting. I just finished the book A Study of Prolonged Fasting (1918), and it pretty much says exactly what you said above. This book is very concise in the measurements they took–this was actually a textbook, and I didn’t know it. The only… Read more »
Devialini De Souza
Guest
Dear Dr. Fung As I have mentioned below, I am an ardent follower of your blogs and I find them very informative not to mention extremely useful. I do have a question though: When my husband was diagnosed with diabetes about 15 years ago, he had dropped from 94kg to 74kg in a matter of a month and a half. The doctor said that this was because he had diabetes (established by doing the Hb1Ac and his triglycerides were way over the top). He definitely lost a great deal of muscle as I remember his thighs being all that!!! His… Read more »
Jane
Guest

I am not a physician or scientist.
Perhaps he lost weight because his pancreas had stopped making insulin? A rapid weight loss is often one of the the signs that alerts people to the onset of Type 1 diabetes.

Wenchypoo
Guest

Speaking of muscle mass, a lot of the historical accounts of fasting mention re-gaining the weight back during a re-feed when the fast was over. Wouldn’t this be the same as yo-yo dieting? Of course, people mainly used fasting as a detox and cleanout, rather than a weight loss method (although a few did use it for weight loss and diabetes control).

Wouldn’t this whole scenario just be a lather-rinse-repeat for the continuation of bad (or wrong) eating habits? My, how far we’ve come medically.

kfacwpup
Admin
Wenchypoo, I typically will lose a pound a day during fasting and gain back .5 pound when I start eating again. So there is net loss of .5 pound per day when I do 3-7 days fasts. [others are successful with shorter fasts, not me] Dr Fung does warn us that we will gain back some of the weight when we start eating again so that is an expectation. The other part is that one is not supposed to continue bad eating habits. If a person does that, they should fully expect to see no improvement. We are coached to… Read more »
BobM
Guest
I have a net loss of close to 50 pounds (depending on the day), but that includes 20-25 using low carb, and the rest using low carb and fasting. I’ve fasted up to five days, have done multiple 3 day fasts, and currently do 16:8 4 days per week, 20:4 two days per week, and one day where I eat 3-4 meals including breakfast. (16:8 = 16 hours with no eating and eating only in an 8 hour window.) I’d like to do longer fasts, but currently have to take aspirin, which must be taken with a meal. I may… Read more »
Sarah
Guest

For me its hard to be on LCHF all the time. I admit that I do go off the LCHF during weekends or if I’m unwell. One interesting thing I noticed after my first 3-day fast is that I can’t eat as much as I used to before. That said, I do plan to continue the 3 day fast once every month or fortnight at least till I reach my goal weight. Maybe even after.

Winston Lee
Guest
1 am 76 years of age, weighing 90 KG with a height of 170 cm. I have type II diabetes for 2 years and am taking blood sugar reducing medications prescribed by my family physician, but never any insulin. For fasting, what precisely are the foods I should take and at what quantities and timings? For me, low blood sugar seems to be more serious than high blood sugar. If I do not take my meals in time, my sugar reading often falls to around 4 or even below and I start to feel dizzy and have to swallow sugar… Read more »
fatso
Guest

thank you Dr jason i have tried your fasting way for curing diabetes 2 and have amazing results here in Zimbabwe . may God bless you, continue to do the good work. Stay blessed

jw
Guest

Dr Fung or anyone, is there any reason blood sugars would rise from Intermittent fasting? Not dangerous levels but higher baseline and PP’s than normal. Other markers are good ie sleep, mood, energy, good appetite control, not experiencing cold etc. Would this mean in a case like this the person is not good candidate for fasting?

BobM
Guest

I had a “fasting” blood sugar test done after fasting for four days, and it was 62. The “normal fasting” (meaning about 12 hours of fasting) test I had done about three months before that was in the low 90s.

ns
Guest

Dr Fung, thx a lot for your great articles. But as i’ve read your good article about Fasting and also this one muscle mass fasting, i have to say the clear meaning of “FASTING” is unknown. research done on 7 day or one month fasting bases does not express all this good result comes out from which kind of fasting??? taking less than 50 calories a day , or 16:8 window diet, or carb diet….. Pls give an advice or fully article about “what is fasting metabolicly, what make your fasting broken ”

thanks so much

Mr B
Guest
Well, I spent much of Sunday reading all of these fasting articles, after a huge meal of eggs and bacon around 2pm. It’s Weds night and I have not eaten anything since that meal on Sunday. I have never fasted longer than maybe 18 hours in my life, and I’m 53. I lost a lot of weight about four years ago on the so-called paleo diet, but I’ve slowly regained about half of it back. After reading Fung’s fasting articles and the entire hormonal series tonight I’m pretty sure that despite very good blood lipid and glucose numbers that I’m… Read more »
Lorenz Mac
Guest

I freakin’ love how comprehensive your posts on fasting are.

I’ve been fasting for 2 years now and I’ve noticed that the best way I can preserve my muscle while fasting is to eat a very high protein meal to break my fast every day. I backload my carbs for night time. This has helped me IMMENSELY with losing fat while still keeping my muscle.

Nancy
Guest

I am on day 9 of a water fast and doing great. My question is, can the beta cell burnout be reversed with a c-peptide result of .57 or is the pancreas too far gone by then?

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Sean
Guest
Hi Dr. Fung, I have couple of blog entry ideas. Is there any chance you could do a blog post on much longer fasts? I mean fasts lasting multiple days and weeks (even months…). I ask for two reasons. First, your very comprehensive content is amazing, but tends to apply mostly to fasts lasting less than 42 hours. Second, I have noticed in the comments that many people are fasting for many days and sometimes weeks at a time (like Jimmy Moore). It would be great to have specific advice for this. Also, I think a blog post that helps… Read more »
Lo Carb Faster
Guest

Awesome post you are a fantastic person and in time I hope many people especially doctors and nutritionists take a reality check and change their ways.

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Keith
Guest
Dr. Fung, Do you have any thoughts about the Protein-Sparing Modified Fast developed by Drs. Bistrian and Blackburn? This is from the beginning of the abstract. “Total fasting reduces hunger and induces rapid weight loss,2 but half the weight loss in the first month and one fourth to one third thereafter is from muscle tissue,3 and hepatic, renal, and endocrine function is affected. For these reasons fasting regimens are generally recommended only for inpatients. Long-term follow-up of persons who previously fasted has demonstrated a high rate of recidivism5 due to obligate regain of lean tissue or the lack of a… Read more »
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Sascha Heid
Guest
Would a single protein-shake a day reduce the hormonal benefits of a fast? My reason for asking is not that i’m terribly concerned about muscle-loss. I did a 5-day water-fast about 6 weeks ago and have not visibly lost muscle. However, i am currently very focused on Lifting and workout several hours a day. Very happy to have holidays now and be able to do that with getting plenty of sleep and reading-time. But if you work out really hard it is mentally really hard to not get any “gains” from that or even just lose a little bit of… Read more »
Ramana Babu
Guest

Hello doctor, I am a type 2 diabetic since 1 year and I am on Metformin 500 mg plus Voglibose 0.3 mg, my question is how to go about the fasting which you are recommending and do I need to stop my medications on the days of fasting. I am overweight also (89 kg for a height of 5 feet 5 inches), pls clarify

Mike
Guest
Dr Fung, I understand your logic and the science behind the minimal loss of lean mass during long term fasting. I am on day 8 and have noted a significant loss of lean mass in the 8 days. I track my weight daily and use an Omron body fat scanner. My weight started at 200.5 lbs with 18.3% BF. I am now at 190 lbs and 17.4% BF. This means I have lost 3.63 lbs of fat which is great but then 6.87 lbs of lean mass. Not good. I have reduced but not eliminated my weight training and have… Read more »
Rhonda Kaye
Guest
Hi Mike, I’m not an expert, but I think there is another possibility you might not be considering. Body fat scanners work by sending a small electrical pulse through your body and reading how quickly it travels. Fat slows down the pulse, but muscle and water both conduct the electricity very quickly, and the meter reads them as being the same. Therefore an electrical fat meter or scanner can only give readings about fat levels. It cannot tell you if the non-fat weight you have lost is indeed lean muscle mass or if it’s actually water weight loss. The other… Read more »
Ann
Guest

I am also wondering why my husband was visibly wasted after a medical fast for seven days for pancreatitis. No nourishment- not even IV – for seven days. He lost 20+ pounds and looked like death. He has been much less muscular ever since. That will be three years ago, in March.

Julian C.
Guest
Hi Dr. Fung, Excellent article as always! I did have one clarification question I was hoping you could shed some light on. Bodybuilders and other athletes often talk about losing strength and lean muscle tissue when cutting, traditionally done through calorie restricted diets. From your article, my understanding is that the preservation of muscle tissue during fasting is due to increased growth hormone (GH) as a result of the fasting. Is it then the case that muscle loss can occur on traditional calorie restricted diets as a result of suppressed GH, since the subjects are not employing fasting to keep… Read more »
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[…] seems to be the complete opposite of what most people would predict, but when you align it with the current trend for intermittent fasting (eat most of your food in a short window each day and fast the majority of the day), it actually […]

Jeff Lippincott
Guest
I have not seen or heard Dr. Fung say before that the human body operates in three different states when it consumes energy to function: (1) the fed state, (2) the restricted-calorie fed state, and (3) the unfed or fasted state. The body when in the unfed state has gone without calorie intake for 6 hours or more. This is when human growth hormone kicks in to save the muscle from being consumed to make sugar for the blood. And I have read in several places that muscle will not be consumed much if any during a fast up to… Read more »
Paul,Kelley
Guest

Jeff, you need to read the book by Dr. Stephen Phinney and Jeff Volek, “The Art and Science of Low Carbohydrate Performance”

Jeff Lippincott
Guest
Hi Paul-Kelley, I’ve now read it. And I stand by my comments above. That book is primarily about living in a constant state of ketosis, and about training to excel at Ironman triathlon type events where one strives to maximize athletic performance at or near their aerobic threshold. Said another way, it is about endurance athletes competing while in the ketogenic state. There is nothing in that book that suggests burning fat is conducive to training for high intensity sporting events by doing resistance training and HIIT workouts. And besides, it takes 2 to 4 weeks to get to a… Read more »
JC
Guest
so… “muscle” break down still occurs…just decreased. One, the tests were done on obese individuals, not body builders or those who just want to gain muscle mass who are not obese. Do you have a known research paper regarding my latter statement? If yes, It would be very nice and informative if you provide. Furthermore, what if a non-obese person fasts? Can you provide a research paper on that? it would help “us” understand your secondhand theories more. Second, The “Protein-retaining effects of growth hormone during fasting involve inhibition of muscle-protein breakdown” research, that you provided, states that “Muscle-protein breakdown… Read more »
Jessica
Guest
I have a question about the “Days of Fasting” chart cited from Dr. Hall’s book. I noticed that x-axis begins with -5 days of fasting, and am wondering why is there a significant change in the oxidation rates of the macro-nutrients already happening before the fast begins at day 0. For example, why would the carb burn rate be going up sharply over the days before the fast even begins? Is there some other pre-fast dietary change at work? Or, is day 0 actually the start of the fast, or does it represent some other time, such as when the… Read more »
Chad
Guest

My guess… people knew they would be fasting for a while and ate more just prior.

abdii
Guest

Dr fung thanks alot for your beautiful work. But could you please reply to JC objections ?
thanks!

Krystian
Guest

Hello and thank you for this blog 🙂
What would happen if a person performs strength exercises (normally done in order to increase muscle mass) during an extended fast, for example lasting 7days. Can body repair micro damages in muscle tissue during this fasting period? If yes, would this process be effective enough to provide muscle mass gain?

Jeff Lippincott
Guest
Fasting is not something that should be done with resistance training. The body has various energy systems it can pull from in order to function. Power lifting and resistance training use the two anaerobic energy systems which control exercises lasting between 1 second and 2 minutes. High intensity interval training (HIIT) workouts also predominantly use the anaerobic energy systems. And these systems burn glycogen (carbs) stored in the body’s liver cells and muscle cells. Fat cannot be used to fuel strength exercises. And if you are on a 7-day fast you are only going to have fat to burn as… Read more »
MachineGhost
Guest

You’re conflating resistance training with endurance training. The latter is horribly catabolic which might as well be the same thing as low calorie starvation.

Jeff Lippincott
Guest
Hi MachineGhost, Isn’t resistance training catabolic if you don’t consume protein, the building block for muscle, soon after completing your workout? And isn’t that similar to low calorie starvation? And what if you do eat soon after the workout, then why was it so important to do the workout during a fast? I was not “conflating” aerobic workouts with anaerobic workouts like you suggest. Did you think I was because I used the term “bonk?” Bonk simply refers to doing athletic endeavors and running out of glycogen stores and therefore the brain doesn’t get its normal fix of glucose. This… Read more »
Traci
Guest

Hi Jeff,
If a person is overweight, then that person has excess protein in their system besides just muscle tissue. Skin and all the extra connective tissue to support that skin consists of proteins correct? So maybe, just maybe it would not only be ok for overweight people to weight train and/or perform HIIT while fasting, but encouraged to increase autophagy of all that loose skin? Also in the examples you listed, these people that are already super lean. THAT I think is the difference.

Jeff Lippincott
Guest
Hi Traci, Weight training and/or HIIT workouts are fine if the person does them while they are in the fed state and have some glycogen stores. Consume some whey protein after the workout, and then commence on your fast. Everything will be fine. But when you are in the middle of a fast and your glycogen stores are depleted you simply do not have the appropriate fuel to use to do quality high intensity workouts. You might be able to do a high intensity effort (or at least think you are) while having only fat to burn for fuel. But… Read more »
jeff k
Guest
i think it’s important to keep your eyes on what’s important. as dr. fung says, so what if you’re protein deficient for a few days? people fasten their attention onto little “defects” in the strategy to avoid facing the big idea of fasting as a way to get healthier. similarly, there are a lot of questions about exercise and muscle maintenance and mini-adjustments in diet and fasting regime. i doubt that these questions have answers. if there were answers they would be statistical and not necessarily applicable to any particular individual. there is enormous variability among individuals. i suspect that… Read more »
Mark Twain
Guest
26 jumbo shrimp not 5. Jumbo shimp is 17% protein, not 100%. You would need to consume 26 jumbo shrimps to compensate for the lost protein assuming it really is “only 100 gram”. But I’ve read some other critcisms on this page that make me doubt a lot you say. Usually it gets attacked with “But Fung is a Doctor, he must be right!” Which doesn’t say much, do you have any idea how many incompetent doctors I know? Fung is far from incompetent, but definitely not infallible and it isn’t the first time I feel his positive representations of… Read more »
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Olaf
Guest

I trust Dr.Fung and switched to water fasting now for to toal of 60kg weight loss

atm I am losing about 700g-800g daily and still have 42kg to go

Khalid Halloumi
Guest

Great article
I have a question though
Some people fast by abstaining from food while still drinking water.
I fast Ramadan for 30 days a year and it’s done with total abstinence from everything even water.
Have there been any comparison between fasting with water or fasting without?
Thanks in advance

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[…] See also: Fasting and Muscle Mass. […]

Steve Bergman
Guest

Table ‘b’, at the top, indicates that the subjects did go into a ‘starvation mode’ while fasting, with BMR falling drastically. At the start, they were burning around 2500 kcal/d. By day 30, their daily caloric expenditure was down to around 1300 kcal/d.

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