Saturday, January 15, 2011

Do you lose muscle if you lift weights after a 24-hour fast? Probably not if you do that regularly

Compensatory adaptation (CA) is an idea that is useful in the understanding of how the body reacts to inputs like dietary intake of macronutrients and exercise. CA is a complex process, because it involves feedback loops, but it leads to adaptations that are fairly general, applying to a large cross-section of the population.

A joke among software developers is that the computer does exactly what you tell it to do, but not necessarily what you want it to do. Similarly, through CA your body responds exactly to the inputs you give it, but not necessarily in the way you would like it to respond. For example, a moderate caloric deficit may lead to slow body fat loss, while a very high caloric deficit may bring body fat loss to a halt.

Strength training seems to lead to various adaptations, which can be understood through the lens provided by CA. One of them is a dramatic increase in the ability of the body to store glycogen, in both liver and muscle. Glycogen is the main fuel used by muscle during anaerobic exercise. Regular strength training causes, over time, glycogen stores to more than double. And about 2.6 the amount of glycogen is also stored as water.

When one looks bigger and becomes stronger as a result of strength training, that is in no small part due to increases in glycogen and water stored. More glycogen stored in muscle leads to more strength, which is essentially a measure of one’s ability to move a certain amount of weight around. More muscle protein is also associated with more strength.

Thinking in terms of CA, the increase in the body’s ability to store glycogen is to be expected, as long as glycogen stores are depleted and replenished on a regular basis. By doing strength training regularly, you are telling your body that you need a lot of glycogen on a regular basis, and the body responds. But if you do not replenish your glycogen stores on a regular basis, you are also sending your body a conflicting message, which is that dietary sources of the substances used to make glycogen are not readily available. Among the substances that are used to make glycogen, the best seems to be the combination of fructose and glucose that one finds in fruits.

Let us assume a 160-lbs untrained person, John, who stored about 100 g of glycogen in his liver, and about 500 g in his muscle cells, before starting a strength training program. Let us assume, conservatively, that after 6 months of training he increased the size of his liver glycogen tank to 150 g. Muscle glycogen storage was also increased, but that is less relevant for the discussion in this post.

Then John fasted for 24 hours before a strength training session, just to see what would happen. While fasting he went about his business, doing light activities, which led to a caloric expenditure of about 100 calories per hour (equivalent to 2400 per day). About 20 percent of that, or 20 calories per hour, came from a combination of blood glucose and ketones. Contrary to popular belief, ketones can always be found in circulation. If only glucose were used, 5 g of glucose per hour would be needed to supply those 20 calories.

During the fast, John’s glucose needs, driven primarily by his brain’s needs, were met by conversion of liver glycogen to blood glucose. His muscle glycogen was pretty much “locked” during the fast; because he was doing only light activities, which rely primarily on fat as fuel. Muscle glycogen is “unlocked” through anaerobic exercise, of which strength training is an instance.

One of the roles of ketones is to spare liver glycogen, delaying the use of muscle protein to make glucose down the road, so the percentage of ketones in circulation in John’s body increased in a way that was inversely proportional to stored liver glycogen. According to this study, after 72 hours fasting about 25 percent of the body’s glucose needs are met by ketones. (This may be an underestimation.)

If we assume a linear increase in ketone concentration, this leads to a 0.69 percent increase in circulating ketones for every 2-hour period. (This is a simplification, as the increase is very likely nonlinear.) So, when we look at John’s liver glycogen tank, it probably went down in a way similar to that depicted on the figure below. The blue bars show liver glycogen at the end of each 2-hour period. The red bars show the approximate amount of glucose consumed during each 2-hour period. Glucose consumed goes down as liver glycogen decreases, because of the increase in blood ketones.

As you can see, after a 24-hour fast, John had about 35 g of glycogen left, which is enough for a few extra hours of fasting. At the 24-hour mark the body had no need to be using muscle protein to generate glucose. Maybe some of that happened, but probably not much if John was relaxed during the fast. (If he was stressed out, stress hormones would have increased blood glucose release significantly.) From the body’s perspective, muscle is “expensive”, whereas body fat is “cheap”. And body fat, converted to free fatty acids, is what is used to produce ketones during a fast.

Blood ketone concentration does not go up dramatically during a 24-hour fast, but it does after a 48-hour fast, when it becomes about 10 times higher. This major increase occurs primarily to spare muscle, including heart muscle. If the increase is much smaller during a 24-hour fast, one can reasonably assume that the body is not going to be using muscle during the fast. It can still rely on liver glycogen, together with a relatively small amount of ketones.

Then John did his strength training, after the 24-hour fast. When he did that, the muscles he used in the exercise session converted locally stored glycogen into lactate. A flood of lactate was secreted into the bloodstream, which was used by his liver to produce glucose and also to replenish liver glycogen a bit. Again, at this stage there was no need for John’s body to use muscle protein to generate glucose.

Counterintuitive as this may sound, the more different muscles John used, the more lactate was made available. If John did 20 sets of isolated bicep curls, for example, his body would not have released enough lactate to meet its glucose needs or replenish liver glycogen. As a result, stress hormones would go up a lot, and his body would send him some alarm signals. One of those signals is a feeling of “pins and needles”, which is sometimes confused with the symptoms of a heart attack.

John worked out various muscle groups for 30 minutes or so, and he did not even feel fatigued. He felt energetic, in part because his blood glucose went up a lot, peaking at 150 mg/dl, to meet muscle needs. This elevated blood glucose was caused by his liver producing blood glucose based on lactate and releasing it into his blood. Muscle glycogen was depleted as a result of that.

Do you lose any muscle if you lift weights after a 24-hour fast?

I don’t think so, if you deplete your glycogen stores by doing strength training on a regular basis, and also replenish them on a regular basis. In fact, your liver glycogen tank will increase in size, and you may find yourself being able to fast for many hours without feeling hungry.

You will feel hungry after the strength training session following the fast though; probably ravenous.


Brooks, G.A., Fahey, T.D., & Baldwin, K.M. (2005). Exercise physiology: Human bioenergetics and its applications. Boston, MA: McGraw-Hill.

Wilmore, J.H., Costill, D.L., & Kenney, W.L. (2007). Physiology of sport and exercise. Champaign, IL: Human Kinetics.


Jimmy Moore said...

Would you like to be an interview guest on "The Livin' La Vida Low-Carb Show" ( E-mail me at if you do. THANK YOU for your consideration!

Zbig said...

Hi Ned,
one point which in my opinion is worth drilling down is the glycogen replenishment.
You seem to support the notion that after a workout one should pretty quickly (to avoid conflicting messages about food availability) load on some glucose-fructose combination.
Another approach thou, which I noticed while listening to Dr. Mauro di Pasquale is this:
you don't need to be hasty in replenishing glycogen stores unless you have to be full for the next event to come, especially if you're an endurance athlete. In fact you do youself a favor avoiding carbs because just after the workout you're super insulin sensitive and this gives a better hormonal response for both fat burning and muscle growing. So the impression I had was that it's even better to stay low-carb after the training and allow for the liver to do its gluconeogenesis job and refill your glycogen stores.

Anonymous said...

ok so that means sucrose is ok then? been 50% fructose and all XD ok, so i my in good shape
( fairly muscular, and lean) minimal training at home, fast 23 hrs every single day, then wrkt fasted 1 hr before my BIG meal
( only do 1 meal) my problem?
carbs, cant stand fruits and vegetables ( condiments) so recently tried lean protein (meat) + one potato PW.. good recovery the other day but made me hungrier than my usual h fat meal( this just after eating !) tried to up the fats, a few yolks with the potato -fried in butter- p same story. satiety takes a bit longer ( 45 mn after my meal im still "thinking") i can ride it but is not as pleasant as my h fat meals + one big glass of 350cc milk,( sometimes with dark chocolate or almonds) so i dont thin i whole milk is enough source 4 my carbs? ( pain) and lately my milk consumption ( and other crap like almonds) is going over the top ... so what should i do? lower the intensity? eat fruit?
brw sorry 4 the sht English

LeonRover said...

One may also think outside the box of fructose/sucrose with protein for replenishment of muscle or liver.

Dried skimmed milk provides equal weights of protein and CHO in the form of lactose. (Assuming you do not have lactase deficiency.)

Anonymous said...

In an article "Lactate vs. CO2 in wounds, sickness, and aging", by Ray Peat, the following statements made me wonder about the wisdom of HIT resistance exercise in the fasted state.

Incidental stresses, such as strenuous exercise combined with fasting (e.g., running or working before eating breakfast) not only directly trigger the production of lactate and ammonia, they also are likely to increase the absorption of bacterial endotoxin from the intestine. Endotoxin is a ubiquitous and chronic stressor. It increases lactate and nitric oxide, poisoning mitochondrial respiration, precipitating the secretion of the adaptive stress hormones, which don't always fully repair the cellular damage.

This was part of a much longer article. Sounds like excessive or improperly handled lactate is bad, very bad.

I wondered if this might stimulate an analysis by you, which would be very useful given the interest in fasted training these days.

David Isaak said...

This is somewhat off-target, but your whole concept of CA seems to support the traditional bodybuilding idea of "mixing it up" and "surprising your muscles" as a way of getting out of ruts and increasing growth.

Also, while I mistrust arguments based on Paleo concepts (not because the logic is unsound, but because the premises of how our distant ancestors lived are generally no more than wild-assed guesses), it also seems that the body might be designed to cope with fluctuations in everything: macronutrient mix, micronutrient availability, total caloric availability, shifting types and amounts of physical activity. So perhaps "regularity" in almost anything is unnatural?

That might be an argument for cycling almost everything.

In "Body by Science," the authors argue that most athletes hugely overtrain, and they argue for increased training intensity and greatly decreased training volume.

They support their arguments by pointing out how many world records and personal bests have been set by atheletes following an enforced period of rest because of injury. To me, that seems not to be an argument for the greatly decreased training volume they suggests, but for intense training interspersed with long periods of no training at all...

LeonRover said...

David Isaak

I agree.

Intensity, recovery, HIIT, hormesis, lack of regularity; these are the characteristics of worthwhile activity and training.


Have you seen the blogs on Obesity Panacea on using accelerometers to characterise borderline sedentarism?

Sedentary Physiology Part I: Not Just the Lack of Physical Activity.

Anonymous said...

so gluconeogenesis? i try to avoid that, some folks dont like that idea ( peter @ hyperlipid) excess protein also spikes insulin, i just need to find the "right combo" for my 50gr carbs p day. guess ill just keep drinking that whole milk, a few extra grams of fat here and there, but at least the casein helps with my daily fasting, i cant say the same about potatoes.

Anne said...

Why should anyone want to fast ?

Have I missed something ? I would never want to fast. I eat low carb Paleo and have no weight problems.

Ned Kock said...

Hi Zbig. It ultimately comes down to numbers. Endurance exercise also uses up muscle glycogen, but at a slower rate. More fat is used than glycogen though, so endurance athletes tend to store more fat in muscle to meet caloric demands. That is CA at play again. Whether that is healthy or not, I am not sure.

Ned Kock said...

Hi Anon. Sucrose is found in fruits and sweet potatoes, so there is nothing inherently wrong with it. If you mean table sugar or regular sodas, I don’t recommend them. They mess up hunger regulation, and have very low nutrition value.

Ned Kock said...

Hi Leon. Lactose breaks down to galactose and glucose. Chronic galactose exposure seems to be associated with accelerated senescence in rats and certain types of cancer in human adults. It seems to be fine for human babies when it comes as part of human breast milk.

Ned Kock said...

Hi Jim (Anon2). Peat’s article seems to refer to lactic acid, which is not the same as lactate. To the best of my knowledge, lactic acid is an acidic form of lactate that is either not produced in muscle, or is produced in very small amounts. Btw, lactate (not lactic acid) is used in medicine as part of IV fluids used for resuscitation.

Also, our ancestors probably faced the following situation frequently enough for it to have applied selective pressure on metabolic processes: having to sprint on an empty stomach, climb a tree for safety, and then eat nothing for hours. For example, after fleeing predators, aggressive prey, or various animals protecting offspring/territory.

Ned Kock said...

Hi David. That is not really off topic; both the article and CA clearly point at cycling as a sound strategy. It also makes evolutionary sense. A second hunt of the same animal, under very similar circumstances, would involve enough variability to lead to muscle fiber recruitment patterns that were different than the first hunt. Transport issues, weather etc. would also ensure some variation in feeding. Even climbing trees to get fruits would involve different muscle activation patterns. Strength training involving the same movements repeatedly, done exactly in the same way, is very unnatural.

Ned Kock said...

Thanks for the Obesity Panacea link and info Leon. Good articles.

Ned Kock said...

Hi Anon3. Whole milk has a lot of sugar in it. There are several alternative low GI options available, including some fruits (e.g., melons, which are also good sources of many other nutrients). One cannot maintain a strength training routine that involves major muscle glycogen depletion on LC for too long. A routine involving short bursts of activity a few times a week is another story. You’ll need enough protein though.

Ned Kock said...

Hi Anne. We all fast for about 1/3 of every 24-h period; but I guess only a few of us would fast for a full 24 h. Some of the best things in terms of health occur during the overnight fast.

js290 said...

My interpretation of Body by Science is they advocate precisely high intensity, low volume followed by "optimal" periods of rest. Any additional "exercise" activity is not necessary. They acknowledge, however, that as people get physically stronger and more fit metabolically, they naturally engage in more physical activity. In the book, they say the average optimal recovery is 7 days. In this interview, John Little explains how they measured that with a BodPod.

Here is an excerpt of a presentation given by Dr. Doug McGuff where he talks about building your workout around your life and not your life around your workouts. It's not uncommon for people who train like this to go 2 weeks or more between training sessions and still show some measurable improvements.

LeonRover said...

Hi Ned

Do you have a references on chronic galactose exposure in rats and humans?
One of our milk companies here in Ireland is selling "lactose free milk", and it is clear the milk has used lactase, or an equivalent, to create the mono-sacchs glucose and galactose.

As always, I am trying to apply Paracelsus' dose toxic Principle.

In the cancer study, is a particular biochemical pathway exhibited in ex-vivo experiments?

LeonRover said...

Hi Ned
There seems to be a link in ovarian cancer - -

however it seems to be a genetic failure in transcripting an enzyme in the pathway.

Ned Kock said...

Hi Leon. I can’t find the reference, but it described something in the lines of a byproduct of galactose facilitating a step in the oncogenesis process. That is, it does not seem to be a straight cause-effect situation, but it doesn’t look good either.

Also, the ability to digest lactose, in human adults, seems to have evolved rather recently in the human species, which makes me suspect that it involves a costly trait. This type of trait tends to evolve late in the evolutionary history of a species:

Anonymous said...

refined or not, if im going to eat sugar, ill rather eat it in my dark chocolate, becuse fruit is disgusting to me. also i fast 23 hrs every single day for numerous reasons. one autophagy, so cancer worries here, ill keep drinking my milk, thankuverymuch

Anonymous said...

Tomoji Tanabe 113 years

did not drink alcohol, just daily milk.

Louisa Shephard 111 years

she attributed her longevity to "hot milk with a dash of whiskey each evening"

Hryhory Nestor, of Ukraine 115 years

he recommends a diet of "milk, cheese and potatoes with an occasional shot of vodka"

Maria Esther de Capovilla 116 years

grew up drinking fresh donkey and cow milk. died eating cake and drinking what? milk

Maria de Jesus dos Santos 115 years > warm milk with sugar

nuff said. vodka for the win. or maybe some industrial milk.

Ned Kock said...

Hi Anon.

As I said before on this blog, I don’t think dairy in general is unhealthy. And the unhealthy aspects of it are not even in the same universe of potential negative health effects as foods rich in refined carbohydrates/sugars, omega-6 fats, and a few other things that are becoming less common (e.g., trans-fats, hydrogenated fats).

Milk has a number of nutrients other than lactose that are health-promoting. Lactose is not the healthiest part of milk.

As for the examples you gave, of centenarians, I suggest you do a little more research on them. My guess is that you’ll find out that longevity runs in their families, and that the majority had a not-too-distant relative who was also a centenarian.

Anonymous said...

what would be the best post workout meal timing if, for the time being, my goal is to get from 14% BF to at least 10-11% rather than to get bulky

suppose, i eat at 6pm (the only meal of the day), then go to sleep at 10pm, wake up at 6am at which point i workout (push ups/pull ups to complete failure and exhaustion) for app. half an hour,then go to school, and eat only at 6pm of that day - would that work?

Avishek said...

Here's something I cannot find answers to:

WHY are ketones elevated post exercise? I've been suspecting this for a while, I notice increased focus about 20-30 minutes after exercising, and its the time I'm about to make food, but this rush of ketones to me brain is telling me something else.. is there an evolutionary advantage? It's like, you just hunted for your dinner, now you must think about how to set up a fire..

Muscle damage causes transport of fatty acids and cholesterol to the muscles, so perhaps that and an overall elevation of fatty acids creates this.

Ned Kock said...

Hi Anon. For optimal nutrient partitioning you should eat soon after the exercise, say between 30 min and 2 h, and fast later. And optimal nutrient partitioning is the key to bringing your body fat percentage down. You want as much protein as possible to go do muscle, as many carbs to go to replenish glycogen etc. You don’t want glycogen stores to be partly replenished through muscle catabolism, and partly based on carbs later.

Also, what you are suggesting may lead to some negative long term adaptations, as the body tends to adapt to everything you throw at it, even though it may accelerate body fat catabolism in the very short term. That is, if you don’t start developing the symptoms of severe hypoglycemia right away.

Have you tried what you are suggesting?

Ned Kock said...

Hi Avishek. Ketones tend to go up when the potential availability of glucose for the brain is reduced. During exercise muscle takes up glucose from the blood to complement other sources. This may be one of the reasons. An adult human has about 5 g of circulating glucose. Bring that down in half, in the absence of ketones, and the brain gets angry. It would take no more than a 10-calorie expenditure to do that, if all the calories came from glucose.

The other reason is that the levels of free fatty acids in circulation go up a lot during intense exercise, because muscle uses them together with sugar. Ketone levels tend to go up together. Ketones are a byproduct of the metabolism of free fatty acids, which is why the two are nearly always elevated together. In this context, which happens also in the absence of exercise (e.g., in LC dieting), if ketones are not used, they are eliminated in the urine.

David Isaak said...

I don't have big issues with dairy, but I lean toward the fermented: cheese, yogurt, kefir. Milk? Never liked it much.

Fermentation knocks the sugars way down, pulls the vitamin content up, and may have some other beneficial effects.

Keith said...

Whatever sports you are doing, you have to do it regularly to gain results. Sometimes it is not as easy as it seems. In order to enhance my strength and gain the most benefits from my workouts I am taking additional nutrition. I have tried a lot of different workout supplements over the years and nothing has given me as much energy and focus as Military Grade Nutrutionals have. In my opinion, their pre-workouts are the most effective supplements.