Thursday, October 29, 2009

Questions & Answers

This is the first in a series of posts with the most useful replies I made in the íntermittent fasting thread on Answers have been edited/updated when needed.


Calorie Restriction (CR) vs Intermittent Fasting

Q: I think CR in general is probably more healthy for some people than "fasting".

A: Depends on how you define "healthy". The whole premise of CR for life extension may sound great on paper, but it's not much fun to chronically restrict calories for rest of your life in order to live a few years more. Especially if the price you pay is hunger and weakness.

Studies hint that IF may have life extension benefits on it's own, some of them are unique to IF and not seen with CR: disease prevention, protection against brain disorders (i.e Alzheimers), immune system support and improved pulmonary function, even on higher calorie intakes.

IF at energy balance > CR.

So perhaps we can get all the benefits of CR, and then some, without having to restrict intake as harshly. Here's an example of some of the exclusive benefits of IF vs CR;

"...Nevertheless, intermittent fasting resulted in beneficial effects that met or exceeded those of caloric restriction including reduced serum glucose and insulin levels and increased resistance of neurons in the brain to excitotoxic stress. Intermittent fasting therefore has beneficial effects on glucose regulation and neuronal resistance to injury in these mice that are independent of caloric intake. "

From "Intermittent fasting dissociates beneficial effects of dietary restriction on glucose metabolism and neuronal resistance to injury from calorie intake" by Anson et al.

Then again, it may be wishful thinking. Main support for the hypothesis comes from animal research, human research is still sparse. However, there are some recent studies that lends support for the hypothesis to be valid for humans as well, for example:

"...These findings demonstrate rapid and sustained beneficial effects of ADCR on the underlying disease process in subjects with asthma, suggesting a novel approach for therapeutic intervention in this disorder. " (the authors conclude that alternate day fasting > CR)

From "Alternate Day Calorie Restriction Improves Clinical Findings and Reduces Markers of Oxidative Stress and Inflammation in Overweight Adults with Moderate Asthma" by Johnson et al.

The mechanism by which fasting protects the heart is not known, but may involve an enhanced ability of cells to cope with oxidative and metabolic stress. Wan et al speculated that...

"A recent study showed that alternate-day caloric restriction can reduce systemic markers of inflammation and oxidative stress and can reduce symptoms in subjects with asthma" (Here they are referring to the human trial by Johnson et al)


"Intermittent Fasting imposes a mild beneficial stress on cells."

And affects adiponectin:

"Adiponectin concentration was twofold greater in the plasma of rats that had been maintained for 3 months on the IF diet"

Conluding that Adiponectin may possibly explain some of the beneficial effects:

"Adiponectin has previously been shown to have cardioprotective and anti-inflammatory actions. "

Yet finishing with some reservations, as the research is still scarce on this topic:

"IF results in changes in levels of several circulating factors including decreased levels of insulin, leptin and cholesterol, and increased levels of testosterone [27]*. It will therefore be important to elucidate the roles for, and interactions, of these different factors in cardiovascular responses to IF. "

* The effects on testosterone seems unique to rodents so far (personal conslusion based on my review of the topic).

The above is from "Cardioprotective effect of intermittent fasting is associated with an elevation of adiponectin levels in rats" by Wan et al. A recent paper discussed the cardioprotective benefits with regards to humans:

"Short-term modified alternate-day fasting: a novel dietary strategy for weight loss and cardioprotection in obese adults" by Varady et al.


I wrote the above almost two years ago (added some recent studies for the sake of context). Since then, there's been some additional findings, though nothing groundbreaking. There's a lot on this topic, but I'm gonna cut it short here. Have written plenty on this in the book. To summarize my response to the question: intermittent fasting may or may not have exclusive benefits which cannot be obtained with a traditional, calorie restricted diet. However, due to the scarcity of research on humans, and due to many confounders present in the available research (i.e some of the studies on IF/ADF does not use a CR control group), it's hard to say anything for certain yet.

Intermittent Fasting and PPOS

Q: The Life Extension Foundation is big on the idea that big meals = elevated post prandial oxidative stress (PPOS) which is obviously a negative. Any opinion on this seemingly negative effect of IF/Big Meals?

A: Studies* show oxidative stress is less on intermittent fasting compared to regular calorie restriction. Yes, even when comparing the same calorie intake with varying meal splits (i.e 3 big meals vs 6-9 small meals). The neuroprotective effects of the fast yields the net effect of PPOS being lesser on IF - despite larger meals.

* in ref to Anson et al.

Catabolism during the fast

Q: So, how long does it take for significant muscular catabolism to start? Over 24 hrs?

A: That's context dependent, but consider that blood glucose is maintained within range mostly by gluconeogenesis beyond the 16 hr mark*. That answer might not make a lot of sense, but eat sufficient amounts of slow releasing protein before going to bed and it shouldn't be an issue even if you go for longer than 16 hrs.**

They key factor in whether you'll lose muscle or not is the severity of calorie deficit, not meal time intervals within a non-retarded range.

* note that the studies looking at this contained nutrional regimens very different from what we are doing (i.e Cahill et all fed test subjects 100 g cho before bed time, no protein, and then had them fast for several days to gauge the rate by which liver glycogen vs gluconeogenesis contributes to maintain blood glucose).

** hell there's even a study out there suggesting proteolytic gene expression does not become turned on until the 40 hr mark or so.

A more recent question on the same topic -

Q: Hey guys, got a question about fasting length. I'm currently IF'ing by doing two 24 hour fasts per week (two days with complete fasting) My question is, could I do both fasts consecutively and do one large 48 hour fast? What is the longest amount of time that it is safe to fast before LBM loss/metabolic downregulation?

A: Safest? Well, consider that de novo gluconeogenesis escalates beyond 16 hrs. 16 hrs is the tipping point - your glucose demands after this point is met primarily (more than 50%) by conversion of stored amino acids into blood glucose. Liver will support the brunt of glucose needs before that point. Theoretically, proteolysis will occur to the greatest extent 24-48 hrs into the fast. Of course, there are numerous confounders here to take into account (i.e a casein heavy meal before the fast will delay proteolysis further).

Metabolic downregulation? Up to 72 hrs according to most studies.


Anonymous said...

Great stuff as always, Martin.

Tim said...

I disagree with one point.

You said muscle loss will be more dependent on the size of the deficit, but as we've seen with properly performed PSMF, muscle loss can be minimal or nonexistent with even these extreme caloric deficits.

I think the claim that the size of the deficit has any effect on muscle loss. What determines that is training status (not killing yourself when dieting but still providing a stimulus) and protein intake. Granted, on larger deficits more protein would be needed to spare muscle loss, but the deficit still isn't directly affecting muscle loss.

Your thoughts Martin?

Tim said...


"I think the claim that the size of the deficit has any effect on muscle loss is false, or at least extremely context dependent."

Martin Berkhan said...

Muscle loss is dependent on

1. body fat percentage

2. size of deficit

3. protein intake

4. training

I've covered this many times.

PSMF is a horrible idea for someone already lean. Generally speaking.

Paula said...

Great post!! I am now documenting my IFing journey at youtube(dot)com/hislivingsacrifice

It would be great for you to post videos along with your blog in an effort to spread the news of IFing.

I recently posted a video showing my results of going from a size 14 to an 8. I follow The Fast-5 Diet so my aim is to fast 19 hours a day with flexibility on the weekends. It's working well for me in releasing body fat.

Al said...


Excellent post. I look forward to more.

What is your recommendation for protein based on grams per pound of BW?


Martin Berkhan said...

'It would be great for you to post videos along with your blog in an effort to spread the news of IFing.'

I'll look into that, thanks, Paula.


it's context dependent. At energy balance and above, 1 g/lb is a good rule of thumb. For dieting purposes, more. Check out one of the earlier Q&A's where I covered this in greater detail.

Mike OD - IF Life said...

Hey Martin,

Good stuff as always. I'd like to know your thoughts about the following quote from Dr Michael Eades (Protein Power author) on the source of amino acids during IF:

"I don’t think IF would affect muscle mass much at all. If you go without food for a long period of time, say, several days, your metabolic system goes after your muscle mass to convert the protein stored there into the glucose you need to keep your blood glucose normal. This doesn’t happen in the short term. All the protein structures in the body draw from and add to the amino acid pool. When muscle breaks down the individual amino acids go into the pool from where they’re harvested by the system that converts them to glucose. When new muscle is made, the amino acids used to construct the muscle protein are drawn from the amino acid pool. One of the contributors to the AA pool is enzymes that are no longer needed and junk proteins that the body is cleansing from the cells. When one is fasting, one of the group of enzymes not really needed is the group of digestive enzymes that would otherwise be employed in digesting food. These enzymes break down and their amino acids enter the AA pool where the muscle can pick them up as needed. Also, during an IF, the body goes into ketosis. I posted a few months back on how ketosis stimulates the process of cellular cleansing by removing junk proteins from the cells. The amino acids from these proteins also enter the AA pool where they can be recycled by the muscle mass. So, even though new protein isn’t coming into the body minute by minute from the diet, there is plenty of substrate there in the AA pool to last until the next meal, which is, at most, only 24 hours away."

Since the whole body is based on protein structures (simplistically stating), how do we know the real % of Amino Acids that are catabolized (and not replenished) from muscle vs other sources after 16hours?

Also one of the touted benefits of IF/CR is the upregulation of "autophagy" where cells consume junk proteins and recycle them (which can also be seen as a slow down of the aging process as well as disease prevention). It would seem that only longer fasts (or very low calorie diets) would stimulate this need for recycling.

Either way, I do enjoy mixing about 3 scoops of BCAAs in a gallon of water and drinking it daily. I find it helps (but I am not also eating over 0.8-1g/lean lb protein)

Mike OD

Half Navajo said...

was just reading the new Mens Health at the bookstore today... mentioned a new study that found people eating 25g of protein, mixed with some carbs before there workout, produced less cortisol, and there metabolism was higher for 24 hours than people who didn't have the pre workout shake.

I have taken your advice on the pre workout meal, awhile ago, and noticed alot more motivation in the gym. Also since ditching the low carb nonsense, and eating potatoes and more fruit again. My favorite pre workout meal is two eggs, hashbrowns, and some grapes.


Anonymous said...

Thanks for taking the time to do this. The IF thread att is such a mess.

Tan Yew Wei said...

I've got a question regarding muscle loss after the 16 hour mark.

This is obviously a very fluid cut off point, and you mention that eating slow releasing proteins in reasonable amounts.

What is a reasonable amount?

If we use the typical 3.5g/hour for milk proteins, does that mean that 56g of milk protein will tie you over for 16 hours and beyond in terms of net nitrogen balance? Does speed of digestion scale linearly?

More importantly, what are the real world results with you and your clients? Finally, if you were to set a certain benchmark value for protein consumption in that final meal, what would it be?

Thanks in advance.

Tim said...

@ Mike OD,

That's an interesting idea.

I do know that approximately 70g of protein daily come from your body digesting enzymes used for digestion. Basically this ties in perfectly with what you posted. During the fast when your body clearly doesn't need digestive enzymes, it will be getting some protein from breaking the enzymes down, which ties you over till you eat. Obviously when you do eat it makes sense that another ~70g would go to remake these digestive enzymes, but as far as the timing goes, it explains why after 16 hours we see more muscle loss. After this point all the enzymes may be broken down and the body starts using muscle as a protein source.

I had never heard about getting protein from digestive enzymes until one of my high level nutrition classes, but it does make sense, and could explain some of the physiological effects of short term fasting.

Martin Berkhan said...


your questions are complex and will be answered in either the book or a future post on the topic.

Martin Berkhan said...


Eades is half right and half wrong. I won't comment much further than that.

'Since the whole body is based on protein structures (simplistically stating), how do we know the real % of Amino Acids that are catabolized (and not replenished) from muscle vs other sources after 16hours?'

There are amino acid tracers for that.

Migue said...

I started doing fasted cardio 30-60min with ECY when i woke up 2 weeks ago, then i wait 8 hours to eat.
All would say that i will lose muscle, strength, etc...well, i checked with caliper, etc...
And the only thing i have lost its almost pure fat, i gain strength each week,
i dont have much strength with my upper body, and i been with the same strength like 1 year.
When i started I.F, i gained some LBS of strength but it stopped.
But when i started the fasted cardio, and eating more, i have gained in 2 weeks 20lbs of strength with arms, back, arms, shoulders, abs and i have maintained strength with my legs, even with every day LISS cardio.

So, what i wanted to said its that losing muscle without eating, even when doing cardio, it could be true but just when food its available, its completely restored all the muscle i had lost in the day and maybe i could gain.

Fasted cardio and then eating a lot of hours later, shows the body that it has to use almost completely the fat stores to produce energy trough all the day, then strength training make the body to conserve all the muscle when in a deficit.

This type of training and eating, really need more studies because some days i ate like 5000kcals of crap, and in the next day i looked better so i think with this approach maybe it really could be possible to lose fat and gain muscle in the same day.

BTW: Sorry for the bad english :p

Tim said...


I agree. Whenever I do LISS and wait a while to eat, I see mostly fat loss and no muscle loss (assuming that I still weight train). It's pretty cool to help shed some fat quickly.

Also Martin did a post on this a while back about an experiment Dr. Mark McCarty did that showed fat loss and some lean gains with only cardio during a fasted time. It was posted August 22, 2009 if you wanna go back and read it.

Martin Berkhan said...

Fasted LISS and meal timing is a non-issue. Fasted HIIT and meal timing is a different animal though, and that's where you might run into trouble if you wait several hours until feeding. Escalating gluconeogeneis (amino acids => glycogen) coupled with increased cortisol doesn't make for a good combo in the fasted state.

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

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