Monday, November 16, 2009

Fasting and Metabolism

Made a few short comments in response to a blog post I just saw on The Fitness Spotlight.

The post is here and below are my responses to some of the claims made.


Just a few short comments on some claims here. Sorry if this has been covered somewhere among the comments, I haven't read through them all.

"Liver glycogen levels are depleted within 8-10 hours. Muscle glycogen falls by 50% over 24-hours, even without exercise. "

False on both accounts. Liver glycogen is completely depleted in approx 28 hrs (Cahill et al). And the second statement is also incorrect. In humans, muscle glycogen is barely affected at all after 24 hrs, assuming no strenous activity.

"After depleting glycogen, amino acids are recycled to be broken down for glycogen through gluconeogenesis. "

This is an ongoing process, but liver glycogen does not need to be depleted in order for amino acids to contribute to the maintenance of blood glucose. The longer the fast, the greater the contribution - for example, after 16 hrs, aminos will start contributing more than 50% to the amount of glucose in your blood stream. After 24-28 hrs, 100%.

"We see increases in three of the four hormones driving lipolysis, indicating a propensity towards fat burning. Somewhere around 12-18 hours, lipolysis becomes a major energy pathway, producing energy from body fat. "

Yes. In fact, after an overnight fast, 2/3 of the energy burnt are free fatty acids. Eat breakfast and you'll be putting the brakes on this process, of course.

"T3 levels fall slightly, indicating a slightly lower metabolic rate. Urinary nitrogen excretion falls, indicating less catabolism of muscle proteins. "

No. Are you looking at rats now again? Because the downregulation of T3 takes more than 72 hrs to occur in humans. A short fast in the 16-24 hr range certainly doesn't impact negatively.


Anonymous said...

great stuff...just what i was looking for in fact.

Anonymous said...

Dude we need your book pretty please:)

Charles R. said...

Interesting, and fits with my experience.

I've been skipping breakfast, but taking some BCAAs and glutamine/alanine dipeptides in the morning. Do you think that would reduce lipolysis?

Martin Berkhan said...

Any time you eat, be it carbs, fat or protein, lipolysis is temporarily reduced or halted. Dose-response.

Tan Yew Wei said...

You Stated that by 16 hrs, amino acids contribute to 50% of the body's energy expenditure.

Firstly, does amino acid use imply muscle as their source and thus muscle loss?

Second, how does the 16 hrs 'rule' change according to variations in calories (if it does at all)? ie: PSMF, 20% below maint, at maint, above maint. I'm sure the paper you cite it from made some assumptions in this regard. If so, would you care to enlighten us.

Thanks for answering all the questions so far, and I'm certainly looking forward to the book.

Anonymous said...

Hi Martin. First of all, I love your webpage. It is, like yo usaid, a non-bullshit approach to getting in shape.

What I wonder is if it is possible to lean out and maintain your weight. For example, I am rather low on BF as it is, however I would love to remain on my current weight and replace the extra padding with muscles. Is this a possible way? For isntance adding 1-2 cardio passes each week or does it all come down to eating healthier food?

mike said...

Martin, what happen to liver and muscle glycogen if someone do first thing in the morning LISS cardio 30-60min, and then wait 8 hours to eat?

I ask this because this is what i started to do 2 weeks ago,
I haven't lose any muscle at all, i even gotten stronger but i want know how much glycogen a LISS cardio of 60min can use

Martin Berkhan said...


'Firstly, does amino acid use imply muscle as their source and thus muscle loss? '

Yes and no. Aminos are going in and out your muscles without causing muscle loss all the time, in between meals and during sleep. Amino acid metabolism is complex. Burning BCAAs does not equal muscle loss, nor does stimulating protein synthesis equal muscle gain. Covering this in the book. Might make a future post on it.

'Second, how does the 16 hrs 'rule' change according to variations in calories (if it does at all)?'

During conditions of calorie deficits, the process would be escalated in proportion to the severity of the calorie deficit imposed on the day prior. Other confounders that may prolong or escalate the process (to which gluconeogenesis contributes to >50%) is amount of carb intake the day prior*

* For example, Cahill gave a test subject 100 g glucose before having him fast and then tracked liver glycogen at various time intervals. From the point of carb ingestion, liver glycogen was completely depleted in approx 28 hrs.

Martin Berkhan said...


Sure, but it's not as easy as just adding some cardio and eating healthier. That being said, I'm not giving individualized guidelines on what to do here, since there is no cookie cutter approach.

Martin Berkhan said...

'Martin, what happen to liver and muscle glycogen if someone do first thing in the morning LISS cardio 30-60min, and then wait 8 hours to eat?'

Liver glycogen will empty a little faster, that's it. Barely anything will happen to muscle glycogen with LISS.

LISS = free fatty acids are mainly used to support the activity, not muscle glycogen.

HIIT = vice versa.

Tan Yew Wei said...

Fantastic Martin! I hope to hear a solid date for the book soon.

Frank said...

Thanks for sharing this, Martin.

UofMWolverine81 said...
This comment has been removed by the author.
UofMWolverine81 said...


Given some of your answers above, what is your general feeling about fasted LISS cardio first thing in the morning when a person is focused on aesthetics (as opposed to athletic/performance-based goals as the top priority)?

This routinely gets a bad rap by various "gurus" who say that at vest is makes little difference in the overall picture and at worst it is counter productive.

Personally I have never agreed with either angle, as I will do everything I can to achieve a goal, even the "minor" stuff....granted the main focus is always on having all the big-ticket areas covered before adding in the little stuff, but I still feel every little bit can always help.

And I have always found it somewhat laughable when the claim is made that it is somehow counterproductive. If I were going out to run a marathon, surely, but I am not running very far unless somebody is chasing me!

Martin Berkhan said...



'HIIT for Fat Loss'

My answer there summarizes my stance on the matter. Fasted state LISS/LISS in general has several benefits if your goals are primarily aesthetically related. For max strength and muscle maintenance during a diet, LISS is superior to HIIT im my experience.

Anonymous said...

hey martin i agree. my squats really suffered when i started doing intervals 2-3x week this summer. i think i lost more mass overall as well. i never had that problem with hiking, cycling or just taking long walks as cardio like i did in the past.


sandro said...

hi Martin

thanks for good info.

I've read that among other things ,body fat is composed by 12% of during fasting could our body use this proteins for its needs??


Martin Berkhan said...


12%, not likely. Not sure where you got that idea from. A fat cell consists of approx 85% triaglycerol and much of the rest is water. Like all cells in the body, some small fraction is made of amino acids, but not the kind to be mobilized and used as a fuel substrate akin to the way we burn of fatty acids.

Alanine and glutamine are the two main amino acids used as a fuel source during fasting (i.e they become glucose via the liver), and these non-essential amino acids can be readily assembled from other amino acids when the need arises - or be directly shuttled to the liver from the gut (glutamine) or muscle (alanine).

Anonymous said...

Hi Martin, Just discovered your site. Awesome posts! I'm going to give "Leangains" IF a try next week. Keep up the good work man:)Terry

James said...

I would just like to add in that my experiences with LISS and HIIT are similar to those mentioned here. HIIT zaps my energy much more than LISS. It leaves very little "oomph" for the gym if I have a HIIT session on the day prior.

Jon (DJTheory9 from lyle's forums) said...


Right now i'm doing EOD refeeds (IF style) with Lyle McDonald's SPF 1.0 protocol twice a week. i'm attempting to do the protocols a.m. (unless my schedule permits me to) and continue to fast up until aprox. the 16 hour mark. I see in one of your responses above that LISS is superior to HIIT. i'm pretty much doing plenty of LISS at work and as a part of the protocols as well. i also adjust calories according to my activity.

Now here is the cool thing, i performed SPF 1.0 yesterday mourning and did IF. today i did legs in the gym and kept volume low and intensity high. (also did IF). My performance for some odd reason was awesome and i felt stronger then usual.

My question to you is, what is going on lol? could it be the depletion from SPF 1.0?

Anonymous said...

fwiw, i've been gaining strength while dieting doing something very similar to you.. 3 weights sessions per week with 2 SFP1 sessions(sometimes SFP2).

I do the weights versions of the SFP's, so im thinking its probably a combination of the practice of the lifts, extra blood flow, and maybe greater insulin sensitivity from depletion + IF causing greater lbm gains... or maybe im completely off haha

Martin Berkhan said...


I was speaking in broad terms. The statement

'For max strength and muscle maintenance during a diet, LISS is superior to HIIT in my experience.'

does not mean that you can't gain or maintain strength while doing HIIT as part of your diet and training plan.

I've used the Stubborn Fat Loss Protocol on several clients with no ill effect. I still use it as part of pre-contest preps or for clients below single digits looking to get leaner. In fact, I helped Lyle test drive the 2.0 protocol, for which I'm mentioned in the foreword to the book.

It's just that for most people, LISS is a better alternative. The great majority is not lean enough to benefit from SFP, nor is metabolic conditioning high on their priority list if they're honest about it. They wanna see abs and that's it.

The only reason most people keep ranting about HIIT is because they think it's vastly superior for fat loss, which it's not. I've covered the true caloric burn of EPOC before (see the post I linked in response to Wolverine). In such cases, LISS is a superior alternative. More arguments for LISS can be found in the link.

Jon (DJTheory9 from lyle's forums) said...

Ok Martin. Just wanting to make sure i'm doing things right instead of doing things wrong lol. I'm really enjoying the program i'm on and IFing just makes things so much easier and more flexible. That is awesome how you helped tested SPF 2.0. i'm going to save that protocol though for when i'm under 10% (hovering at 13% right now).

I'm also going to bulk IF style since people (such as JC over at got good results doing it. its just funny how everyone i talk to finds IF as a BS program and look at me as if i'm crazy...ehh ignorance. keep up the good work Martin!

Mike OD - Fitness Spotlight said...


What is your take on this study I found through Brad Pilon:

Which when comparing a group of exercisers who either drank water or a C+P group, has no net difference in net muscle protein synthesis when you look at 9 hours pwo.

Which also states:
"We conclude that, even in a fed state, protein and carbohydrate supplementation stimulates muscle protein synthesis during exercise. Ingestion of protein with carbohydrate during and immediately after exercise improves WHOLE-body protein synthesis but does not further augment MUSCLE protein synthesis rates during 9 h of subsequent overnight recovery."

So...if I am reading that right, as long as one eats enough calories/protein, the size or timing of the eating window is not vital for muscle protein synthesis.

What are your thoughts on this?

Mike OD

Martin Berkhan said...


Did you read the full text version?

Do you think it's surprising that the miniscule amount of protein and cho provided post-workout did not stimulate muscle protein synthesis throughout the entire recovery period?

From the discussion -

'The fact that the mean muscle protein synthesis rate
assessed over the entire 9-h overnight recovery period did not
differ between groups might be attributed to the inability of the
dietary regimen to elevate overnight plasma amino acid availability and/or increase circulating plasma insulin concentrations.'

...And it speaks highly in favor of the approach I'm advocating.

'Increasing plasma
insulin and/or amino acid availability during the night, either by i.v. infusion of amino acids and/or the ingestion of more slowly digestible protein sources may represent interesting strategies to augment muscle protein accretion during the night.'

Marek B. said...

Hi Martin!

I've been searching for some studies for a little article I'm writing about meal frequency for my fellow students at the university of Halmstad.
I'm searching for the study that's backing up your arguments about T3. The best I could find was this abstract of "Starvation-induced alterations of circulating thyroid hormone concentrations in man" where their conclusion was: "The range of decrease for T3 in all subjects varied from 24% to 55%." (after 60h of fasting). I would be very thankful if you could tell me the name of the study you're referring to here.


Anonymous said...

I just signed up to your blogs rss feed. Will you post more on this subject?

James said...

Hey Martin, I'm curious about liver glycogen; would it be feasible to simply consume ~80g fructose on workout days and minimal fructose on off days in hope to fully fill the stores on workout days (I've seen about 90-100g to be the cap) and to ensure that they won't empty until the next workout?

Monday: 80g fructose --> Mostly full
T: 10-15g fructose --> Replenishes a bit of the lost fructose, nearly depleted by time of tomorrow's workout
W: 80g fructose --> Mostly full again
etc, for a M/W/F split

Basically trying to maximize fructose intake on workout days and attempt to not have a ton of spillover into apidose tissue.

Apologies if this isn't clear, never been a good writer.

My name is Martin Berkhan and I work as a nutritional consultant, magazine writer and personal trainer.

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