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| Image 1: One reason why IF works is that it breaks the unnatural constant and convenient availability of high energy food and the subsequent suppression of AMPK phosphorylation (img courtesy of foxsearchlight) |
In the
last installments of this series we have begun to dig deeper into the signaling mechanisms that are / could be involved in the beneficial effects intermittent fasting is hailed for in the (unreal) world of the Internet blogosphere. We have identified
AMPK and mTOR as the two players in the constructive and de-/re-constructive orchestrate of mammalian organisms and we have learned that their relationship - despite all its antagonistic aspects - is, after all, a
complementary one. This means that, as you can observe it time and again in nature, health, vitality, yes even sustainable changes in body composition require
balance!The
delicate balance between mTOR and AMPK, this was another result of our considerations, is oftentimes broken in these days of nutritional abundance, where the rebuild and repair mechanisms of AMPK hardly get a chance to control the growth processes a constantly elevated mTOR pathway is triggering. The forced feeding-breaks on an intermittent fasting regime break this rampantly anabolic cycle. They let AMPK come into it's own and allow for...
- ...broken DNA strands to be fixed, before their (re-)use results in cancerous growth (Habib. 2010),
- ...cancer and defect cells to initiate apoptosis, i.e. to kill themselves (Chen. 2011)
- ...life extension via reduction of dietary glucose to work (Schulz. 2007)
- ...fat to be used as a substrate (Hardy. 2002),
- ...inhibiting adipogenesis = fat cell differntiation (Lee. 2011)
- ...mitochondrial biogenesis to be initiated (Zong. 2002),
- ...muscular GLUT4 activity and thus glucose uptake to be restored/increased (Holmes. 1999),
- ...gluconeogensis in the liver to be suppressed (Rutter. 2003),
- ...much much more healthy stuff ;-)
AMPK may be non-anabolic, but that is not necessarily a bad thing! |
Image 2: Who would you prefer to be? Canto (left), on a life-extension (low calorie) diet with chronically elevated AMPK levels, or Owen (right), who enjoys his bananas to the fullest without even knowing about their profound effects on mTOR expression? (image taken from an article in the Irish Medical Times)
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On the other hand, we have also acknowledged the
beneficial effects of mTOR on muscle growth, cell differentiation and many of the other processes that make life worth living and come to a hold, in the only physiological condition with chronically elevated AMPK levels, which is a "life" (if you want to call it such) extending low calorie diet, like the one poor Canto (image 2, left) has been on for a life, I personally would call miserable, when compared to that of Owen (image 2, right) who obviously got his share of bananas.
Moreover, studies on the effects of the AMPK inducing drug AICAR (cf.
previous news on AICAR) suggest that the increase in mitochondrial oxidation may also lead to
dangerously high levels of radical oxygen specimen (ROS) formation (
Kim. 2006), of which you have learned
only recently, that there is a fine line between the benefits of some vs. the deleterious effects of too much free radicals. Which brings up - yet again! - the issue of
balance!
Reversing perspectives: "Low energy" as the normIn the
previous episode, we have also identified energy availability or, to be precise, the ratio of the high energy ATP (adenosine triphosphate) to the lower energy ADP (adenosine diphosphate; -7.3kcal/mol) and AMP (adenosine monophosphate; -10.9kcal), as a crucial determinant of AMPK activation. In one of the most recent reviews on the topic (
Carlin. 2011), David Carlin and colleagues from the
Imperial College in London state that
[...] the finding that ADP, as well as AMP, protects AMPK against dephosphorylation influences the way we look at the physiological regulation of AMPK. To the best of our current understanding, the concentration of ADP in mammalian cells is much higher (10- to 100-fold)
than that of free AMP, and so it is likely to be the main regulator of AMPK activity under normal energy-stress conditions. The extent of the tighter binding of ADP to AMPK, relative to MgATP, essentially offsets the higher physiological concentration of MgATP. An interesting possibility is that under most conditions AMPK is regulated by the ATP:ADP ratio through changes in Thr172 phosphorylation state. Under severe stress conditions, however, when the concentration of AMP might increase markedly, the additional allosteric activation mediated by AMP could act as a type of fail-safe device, ensuring that all AMPK substrates are maximally phosphorylated.
In other words, under normal conditions ADP, i.e. the higher energy variety of the dephosphorylated ATP molecule, and not AMP is the main determinant of AMPK activity. And, and this is a pretty novel finding, both ADP and AMP do not actually activate
5' adenosine monophosphate-activated protein kinase (AMPK), but rather
prevent it from being deactivated. While it may seem that this does not really matter, looking at things this way let's the "deactivation of AMPK by energy abundance" - a state we have accepted as a norm - suddenly look like the exception; and when we come to think of it, all the "diabesity"-related ailments an ever-increasing percentage of our society is experiencing can be tracked back to
the reversal of norm (=AMPK phosphorylated = restore and repair using stored energy) and exception (=mTOR phosphorylated = build, grow, store) that is triggered by the persistent abundance of energy.
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| Image 3: This is the way "fast food" is supposed to look like |
I think I do not have to tell you how to "restore" a normal state, which is characterized by recurrent episodes of increasing ADP levels: Exercise and fasting, or for the paleo crowd out there
"hunting and gathering". I often make fun of the 1001 self-proclaimed paleo experts who try to explain everything based on largely non-verifiable assumptions about how our ancestors lived, but in this case, it is just plain obvious that
"fast food", back in the day, was a rabbit that was too fast to be caught and not a hamburger, which, despite its greasy look, has about 2x more carbohydrates than fat (
CalorieCount).
What I am trying to say, here is that
in human history, exercise or at least "movement" usually preceded nutrient availability. To facilitate that nature has equipped us with a compulsion to move most that is most prominent in anorexic patients, whose desire to "get going" is in part (another factor, these days, is obviously the hilarious calories-in-calories-out conception) mediated by the same mechanism that triggers the "food seeking behavior" in rats (
Guisinger. 2003). With the neolithic age "food seeking" has become obsolete and with the advent of
modern fast and
convenient foods the movements we are making to avail us of the next (mostly sugary) snack or meal, whenever our body senses that the energy level is about to drop to normal (notice the change in perspective), takes us from the couch to the fridge and back... but I am digressing from the topic at hand, so let's get back to how intermittent fasting plays into that.
Intermittent fasting = resisting the urge to go to the fridgeObviously your usual "walk" to the refrigerator is a definitive "no-no", when you are on in intermittent fast - or, to get back to the paleo metaphor,
you are like Paleo Eve waiting for Paleo Adam to bring the "fast food" he is just chasing (the rabbit from image 3) home for you to roast it (I assume you will have read that
doing the same with potatoes is not a good idea). While you are sitting there (on the couch or at the fire place, whatever you like better ;-) the majority of your
5' adenosine monophosphate-activated protein kinase will obviously
stay in the same phosphorylated state it was, when you woke up this morning. This, in turn, brings up the question
when / how the enzyme (AMPK) gets phosphorylated in the first place. A question you will probably be able to answer, if you read
yesterday's news item on the
effects of postprandial carbohydrate, leucine or carb + leu feeding on muscle protein synthesis.
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| Figure 1: Postprandial changes in AMPK activity (relative to fasted state) 0min, 90min and 180min post ingestion of a 4g meal and following supplementation with water (control), carbohydrate (CHO), leucine (Leu), or leucine + carbohydrate 135min after the ingestion of the meal (data adapted from Wilson. 2011) |
If you take another look at the AMPK response to feeding and subsequent supplementation (135min post 4g of chow) you will notice that there is a decline in AMPK that corresponds to the peak in protein synthesis at 90min post ingestion of the meal. If you literally sit through (on the sofa or beyond the fire place
without eating), AMPK will have reached it's former max again (and in the Wilson study peak even higher) another 90 minutes later. Thus
the general recommendation to eat every 2-3 hours would leave little to no time for of normal / elevated AMPK levels during the day - this does certainly benefit muscle protein synthesis, as the latter - the results from the Wilson study confirm that - would be constantly elevated.
In spite of the relatively rapid "restoration" of AMPK phosphorylation in response to "not eating", sitting on the sofa, watching TV and worrying about when you can finally break the fast is not what you would expect to give your physique the edge you are probably trying to achieve.
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| Figure 2: Weight of fat pads in g/100g body weight in AICAR (intraperitoneal injections @ 0.7g/kg body weight) treated vs. control male Wistar rats after 4 and 8 weeks of treatment (data adapted from Gaidhu. 2011) |
On the other hand, Tipton et al. report that as you approach glycogen-depletion (your liver glycogen stores will be depleted within ~16h, cf.
previous installments of the series), your
basal AMPK activity will be elevated up to 2.5x (
Tipton. 2006) - even if you are just sitting on the sofa! Moreover, chronic stimulation of AMPK via AICAR administration in a 2011 has been shown to have a exactly that beneficial modulatory effect on adipose tissue, that would be required for those type of changes, the health and fitness community generally labels as "recompositioning effects" (Ghaidu. 2011, cf. figure 2). Interestingly,
the scientists did not observe any changes in lean mass (meaning you do not necessarily lose muscle when you deliberately increase AMPK), but - and this will remind you of the
effects of high intensity interval training, you have read about, here at the SuppVersity earlier this week - chronically high levels of phosphorylated AMPK did
increase mitochondrial density and energy expenditure (cf. figures 3-4).
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Figure 3: Inguinal mytochondrial density in AICAR
(data adapted from Gaidhu. 2011) | Figure 4: Energy expenditure in kcal/h
(data adapted from Gaidhu. 2011) |
What would you say? Leaning out and setting the scene to stay lean by increasing the capacity to burn energy consequent to a >100% increase in mitochondrial density does not sound too bad, does it?
Optimizing AMPK during the fast by exerciseFrom
previous installments of this series you know that the current "fitness-oriented interpretation of intermittent fasting", as I would like to call it, prescribes exercise as an obligatory 2nd element of a body recompositioning scheme à la leangains.com. It probably does not take a rocket scientists to gather that the energy depriving character of exercise will deplete cellular ATP levels, increase the APD:ATP ratio and thus prevent the dephosphorylation of AMPK. But if this is in fact the case (and it is, cf. "
Exercise is perhaps the most powerful physiological activator of AMPK",
Richter. 2009 ;-), the next question would be:
How on earth can you still build muscle, if exercise activates AMPK and AMPK reduces protein synthesis? Well, the answer is simple: It's the seesaw principle!
fast + exercise > AMPK up || rest + feed > AMPK down
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| Figure 5: AMPK and protein synthetic response (relative to basal levels) to resistance exercise in 7 men and 4 women (data calculated based on Dreyer. 2006) |
In this context, the results of a 2006 study by Dreyer et al. (
Dreyer. 2006) are quite exemplary. The scientists
investigated the effects of resistance training in a fasted state (notice that AMPK is nothing only endless cardio sessions will promote) on AMPK phosphorylation and protein synthesis in 11 healthy young subjects. As the data in figure 5 goes to show, there was the expected increase in AMPK phosphorylation (+89% over baseline) during the exercise session, BUT despite constantly elevated AMPK levels, the protein synthesis, which had dropped to about 71% of baseline during exercise increased to +134% and +147% in the post-exercise period. This is initially counter-intuitive, because
if AMPK were the sole deteriment of protein synthesis, the post-exercise rise in protein synthesis, Dreyer et al. observed should not have occurred. So how can we explain this "paradox"? The answer is pretty simple:
Exercise is in itself a trigger for muscle protein synthesis (
Drummond. 2009)!
And if you remember the two posts on "glycogen-free muscle growth" related to the 2011 study by Camera et al. you will be aware that the phosphorylation of p70s6k and the subsequent
increase in protein synthesis following resistance exercises does occur, even if you train in a glycogen-depleted state.
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Image 4: Duong at the beginning and
end of his 12-week intermittent fasting
body transformation program;
click here to read more |
Furthermore, the desirable (in terms of fat loss) increase in AMPK does not occur, if resistance training is performed in a fed state (
Wittard. 2009). It should thus not be surprising that people like
Duong (cf. image 4), in whose approach to intermittent fasting, training "on empty", i.e. at least without prior repletion of muscular glycogen stores by the consumption of great amounts of carbohydrates prior to his training sessions, was a staple, managed to achieve what everyone appears to be after these days, which is to
lose fat and gain muscle (or at least maintain) muscle weight, at the same time! In that, the provision of supplemental BCAAs before resistance exercise (another of Duong's staples) could help prevent unwanted muscle breakdown, and increase the mTOR response
without decreasing the exercise-induced increase in AMPK phosphorylation that is so beneficial in terms of metabolic health and, of course, fat loss.
With that, I will leave you hungry for more until tomorrow, where due to a national holiday, here in Germany, I will have time to continue my elaborations on AMPK's role in intermittent fasting and beyond. So, I would suggest, you
come back tomorrow if you want more information on how to modulate AMPK and its effects on your physique by exercise, sleep and supplementation to make your intermittent fast (or whatever other diet you are following) even more productive!
