Carnitine as Repartitioning Agent? IGF-1, p-AKT & mTOR Up, Catabolic Proteins Down + 7% Improvement in Lean- to Total Mass Ratio W/ HED of 1-1.5 of Carnitine/Day

It won't spare you the sweat, but carnitine could make it even more worthwhile by ramping up the anabolic and shutting down the catabolic signals.

Until 2006 l-carnitine has been known as a fat-burner, an in-effective fat-burner and an expensive and pretty useless supplement (depending on whom you were asking). Then, in July 2006, Kraemer et al. published a paper (a human study, above all!) in the journal Medicine & Science in Sports and Exercise a consequential paper so to say; a paper in which the authors report that l-carnitine l-tartrate supplementation at a dosage of 2.933g/day (this amount of LCLT contains 2g of pure carnitine) led to a statistically significant increase in androgen receptors in the vastus lateralis after a heavy resistance training protocol in previously strength trained male subjects (Kraemer. 2006).

Still, the evidence has always been inconclusive to say the least

Despite the fact that the concomitantly elevated post-workout luteinizing hormone levels (+19%) Kreamer et al. observed would tell you that the testosterone that would have been necessary to activate those receptors was already on its way, I have never considered this study as convincing evidence of the anabolic prowess of l-carnitine. Plus, let's be honest, differences in whatever serum markers in response to an acute bout of resistance training have failed us way too often, not to look at studies like these with appropriate skepticism.

Do you remember the Ratames study from 2005? The one that showed that high volume training lowers the no. of androgen receptors on the trained muscles? This certainly makes l-carnitine sound like the perfect addition to high volume routines, right? (learn more)

That the same principle of "calm down and don't get too excited over the results of a single trial" does all the more apply to rodent studies should be self-evident and still, science is all about taking each and every experimental result into account to form a theory that can explain all of them, or, alternatively, is able to bust short-comings in previous studies that don't comply with the predictions of the respective theory.

Now, the soon-to-be-published paper by Janine Keller and her colleagues from the University of Giessen (Germany) certainly qualifies as part of the evidence we simply cannot ignore, when we are looking for evidence in support of the theory that l-carnitine could be an overlooked muscle builder or repartitioning agent.

After all, their observation of decreased levels of the proteolytic (=catabolic) MuRF1 protein, as well as the ubiquitin-protein conjugates, which are increased in catabolic states such as starvation and atrophy denervation (cf. Wing. 1995) , alone, would signify that l-carnitine could make a valuable addition to everybody's supplementation regimen.

Lower catabolism + increased anabolism = ???

There is more, however, the addition of 1250 mg L-carnitine/kg to a basally "low carnitine" vegetarian diet also led to significant increases in systemic IGF-1 concentrations in plasma and a local increase in the activity of the PI3K/Akt/FoXO-1 signalling pathway (see figure 1)

Figure 1: IGF-1 mRNA and serum levels, as well as the muscle specific expression and phosphorylation (ph) Akt, mTOR & co after four weeks on the low or high carnitine diets (Keller. 2013)

These results do yet not stand in isolation as the ones by Kraemer et al. still do. Other recent studies by the same research group in Giessen, as well as colleagues from the University of Barcelona have already confirmed the anti-catabolic effects of l-carnitine in piglets and a cancer cachexia model in rodents, respectively (Keller. 2012; Busquets. 2012).

"And you are telling me that works in humans, as well? "

What's the best form of carnitine to take to elicit these effects: I knew you would ask this, so I react to two facebook questions by adding this red box willingly admitting that I just cannot tell you what the best form of carnitine is. There simply is no study that would compare e.g. acetyl-l-carnitine (ALCAR) and l-carnitine l-tartrate (LCLT) in a scenario that would be relevant to the above question. What I can tell you though, is that it appears as if you were better off with LCLT than with ALCAR, if your goal is to top off your intra-muscular carnitine levels. That being said, even normal creatine can do that - you will just have to take more of it. If you are looking for more information you can check out the part of the Amino Acids for Super Humans Series that's dealing with "the carnitines", here.

In this context it does yet also have to be mentioned that the effects of l-carnitine are at least in part species specific. How we know that? Well, in contrast to the said study by Basquets et al. the provision of an carnitine to piglets (Keller. 2012) did not only reduce the MuRF-1 expression, but also the level of its likewise catabolic E3 ligase cousin atrogin-1.

"It has been shown that myofibrillar proteins, like myosin light chain proteins are the main targets of MuRF1for ubiquitination. Thus, carnitine might suppress particularly the degradation of myofibrillar proteins, which under physiological conditions comprise around 60% of total muscle proteins. In contrast to MuRF1, atrogin-1 tags primarily proteins for degradation which are important for controlling protein synthesis and myoblast differentiation, like myogenic factor MyoD, myogenin and the eukaryotic initiation factor of protein synthesis eIF3-f." (Keller. 2013)

With pigs usually being a superior model of the human physiology, this would suggest that the anti-catabolic effects l-carnitine could have on humans are probably more, not less pronounced than those that were observed in previous rodent studies.

Whether the same goes for the IGF-1 response cannot be said, but just like the anticatabolic effects, the pro-anabolic increase in IGF-1 has been observed in previous trials, including a human trial by Di Marzio et al. who observed a significant increase in IGF-1 in HIV patients in response to the provision of 3g/day of acetyl-l-carnitine (Di Marzio. 1999). In the absence of the existing evidence from animal studies, these results would yet have little significance for healthy human beings, whose growth hormone and IGF-1 levels are not rock bottom to begin with (Viganò. 2003).

---

Bottom line: Irrespective of the absence of human data on the IGF-1 boosting effects from non-HIV patients - or even better in training scenarios - it would warrant future studies if an adequate amount of carnitine in the diet can exert beneficial effects in non-obese human beings. For the "sedentary", or let's rather say non-exercised rodents in the study at hand, the latter was a mere fat loss effect - despite the elevations in p-AKT, m-TOR, IGF-1 and the overall more "anabolic" state the rodents were in their lean body mass was not increased compared to their peers on the low carnitine diet.

"Just another set!" ... "I don't know man, we've already pumped away 100,000kg today... do you really believe that's productive, I mean, yeah, we are cuttin', but still" ...learn what this dialog is all about and whether and if / when "another set" is / isn't a good idea (read more)

The lean-to-total mass ratio of the rodents, on the other hand was ~7% higher in the rodents in the high carnitine group. If we do however take into consideration that most of you will not be vegetarians and thus not similarly carnitine deprived as the rodents in the control group on the <1mg/kg carnitine diets, it is highly questionable if the addition of the human equivalent of the 1.25g/kg chow, i.e. 15mg/kg body weight (HED) would actually yield any measurable benefit to non-vegetarians - irrespective of whether they train or not. After all, even the average omnivore human being consumes 100-300mg of carnitine per day (Broquist. 1994), so that the difference between your basal carnitine intake and the supplemental equivalent dose of 1050-1500mg/day is more than 100x lower than the exorbitant difference between the low (if not deficient) carnitine diet in Keller's rodent study at hand (remember: the basal diet had less than 1mg/kg chow; the supplemented diet hat 1250mg/kg diet!).

So what's the verdict then? I guess, I will leave the final words to Burke et al. who reviewed the usefulness of carnitine as an ergogenic aid in one of the first installments of the "A-Z Supplement Review" in the British Journal of Sports Medicine and wrote "future work with l-carnitine may also find some useful outcomes" (Burke. 2009) - needless, to say that the SuppVersity is going to be the place, where you will read about it first ;-)


References:

• Broquist HP. Carnitine. In Shils ME, Olson JA, Shike M (eds): "Modern Nutrition in Health and Disease." Malvern, PA: Lea & Febiger, 1994. 459– 465.
• Burke LM, Castell LM, Stear SJ, Rogers PJ, Blomstrand E, Gurr S, Mitchell N, Stephens FB, Greenhaff PL. BJSM reviews: A-Z of nutritional supplements: dietary supplements, sports nutrition foods and ergogenic aids for health and performance Part 4. Br J Sports Med. 2009 Dec;43(14):1088-90.
• Busquets S, Serpe R, Toledo M, Betancourt A, Marmonti E, Orpí M, Pin F, Capdevila E, Madeddu C, López-Soriano FJ, Mantovani G, Macciò A, Argilés JM:  l-Carnitine: An adequate supplement for a multi-targeted anti-wasting therapy in cancer.  Clin Nutr. 2012;31:889–895.
• Di Marzio L, Moretti S, D'Alò S, Zazzeroni F, Marcellini S, Smacchia C, Alesse E, Cifone MG, De Simone C. Acetyl-L-carnitine administration increases insulin-like growth factor 1 levels in asymptomatic HIV-1-infected subjects: correlation with its suppressive effect on lymphocyte apoptosis and ceramide generation. Clin Immunol. 1999 Jul;92(1):103-10.
• Glass DJ:  Signalling pathways that mediate skeletal muscle hypertrophy and atrophy. Nat Cell Biol. 2003; 5:87–90 .
• Kraemer WJ, Spiering BA, Volek JS, Ratamess NA, Sharman MJ, Rubin MR, French DN, Silvestre R, Hatfield DL, Van Heest JL, Vingren JL, Judelson DA, Deschenes MR, Maresh CM. Androgenic responses to resistance exercise: effects of feeding and L-carnitine. Med Sci Sports Exerc. 2006 Jul;38(7):1288-96.
• Keller J, Ringseis R, Koc A, Lukas I, Kluge H, Eder K:  Supplementation with l-carnitine downregulates genes of the ubiquitin proteasome system in the skeletal muscle and liver of piglets. Animal. 2012;6:70–78.  
• Keller J, Couturie A, Haferkamp M, Most E, Eder K. Supplementation of carnitine leads to an activation of the IGF-1/PI3K/Akt signalling pathway and down regulates the E3 ligase MuRF1 in skeletal muscle of rats. Nutrition & Metabolism. 2013; 10:28. 
• Lösel D, Rehfeldt C. Effects of l-carnitine supplementation to suckling piglets on carcass and meat quality at market age. Animal. 2013 Mar 11:1-8.
• Salama AF, Kasem SM, Tousson E, Elsisy MK. Protective role of L-carnitine and vitamin E on the testis of atherosclerotic rats. Toxicol Ind Health. 2013 Feb 13.
• Viganò A, Mora S, Brambilla P, Schneider L, Merlo M, Monti LD, Manzoni P. Impaired growth hormone secretion correlates with visceral adiposity in highly active antiretroviral treated HIV-infected adolescents. AIDS. 2003 Jul 4;17(10):1435-41.
• Wing SS, Haas AL, Goldberg AL. Increase in ubiquitin-protein conjugates concomitant with the increase in proteolysis in rat skeletal muscle during starvation and atrophy denervation. Biochem J. 1995 May 1;307 ( Pt 3):639-45.

Where Protein Fails, Protein + Resistance Training Succeed: Lifting Corrects Diet-Induced Decrease in Postprandial Protein Synthesis, But Fails to Normalize Net Retention

It takes pains to maintain your gains!

You will certainly remember the shocking revelation that simply eating more protein is not going to prevent the diet induced muscle loss that occurs whenever you consume less energy than you expend (read up on "Protein Intake & Muscle Catabolism: Fasting Gnaws on Your Muscle Tissue and Abundance Causes Wastefulness" | go for it!)...

Don't rejoice, the study at hand does not refute this - protein is still unable to counter the increase in atrogin-1 and other muscle cannibalizing proteins, but there is a "tweak" by the means of which you can at least avoid that its pro-anabolic affects are also impaired.

You can learn more about protein intake at the SuppVersity

Are You Protein Wheysting?

Cod protein for recovery

Protein requ. of athletes

High EAA protein for fat loss

Fast vs. slow protein

Too much ado about protein?

What this "tweak" is? Well, that's easy: Heavy lifting. If you are familiar with the "muscle loss in zero gravity" research that has been conducted by and for the NASA in the past decades (e.g. Ferrando. 2002).this shouldn't surprise you. The NASA studies have after all shown quite conclusively that compared to bed-rest / chronic skeletal muscle unloading, starving yourself is almost "anabolic". No wonder that lifting heavy objects, and not dietary protein is the #1 when it comes to saving your muscular ass from shriveling away on a long and hard diet.

Why does resistance training work, if protein fails?

As discussed in "Protein Intake & Muscle Catabolism" (read it!), it's not a question of the pro-anabolic effects. You, as a suppversity reader know that the p-AKT/mTOR pathway that's activated by protein feeding is sufficient to increase the influx of protein into the musculature. What your beloved protein can't do, though, is to reset a different switch: The "sacrifice muscle to fuel more fundamental metabolic demands switch" which is triggered whenever you are in a long(er) term energy deficit.

"Training For Gains: High Intensity, Low Volume Strength Gains Stick." | more

So what can be done then? Well,... as it is so often the case, the answer lies - once more - open before our eyes: Hit the weights, down the protein and kick your diet's catabolic ass!

I know this sounds too easy, but if you take a peek at the weight loss diets of the average physique athlete and their appearance on stage, it stands out of question that the combination of resistance training and strategic protein supplementation spares muscle mass.

Now the verb "to spare", according to the Oxford English Dictionary, means "to leave (a person) unhurt" (OED.COM), which is - and you probably expected this already, not really accurate. Even the latest data from the School of Medical Sciences at the RMIT University in Melbourne and the Exercise Metabolism Research Group at the Department of Kinesiology of the McMaster University in Hamilton, Ontario, Canada, and the Canadian Sport Institute clearly demonstrates that you cannot switch the diet-induced protein wasting off, completely (Areta. 2014).

Figure 1: The large inter-individual differences make it virtually impossible to tell, whether the MURF-1 levels increased. The similarly catabolic (see overview in the middle) atrogin was yet significantly increased in the early (15g) and late phase (30g) after the workout during ED (Gumucio. 2013; Areta. 2014)

In the corresponding experiment, 16 young, healthy, resistance trained subjects (8 females, 8 males) who had been fed individualized pre-packaged meals delivering 45 kcal/kg FFM (macros: PRO / CHO / FAT 1.4-1.6, 3-3.5 and 0.5-1.5 g·kg BM) per day for five days before they went on a standardized energy 30% energy reduced diet containing approximately

• 1.4-1.6g protein per kg total body mass, 
• 4.0-4.5g carbohydrates per kg total body mass and
• 1.5-2.5g fat per kg total body mass

for another five days. At the end of this "ED" period and five days on rations with only 30kcal/kg fat free mass, all subjects performed a standardized leg press workout (warmup + 6 sets of 8 repetitions at ~80% 1 RM with 3 min rest between set) that was followed by the ingestion of either 15g or 30g of whey protein or an isocaloric placebo.

Figure 2: SLC7A5 AA transporter expression (left) and myofibrillar fractional protein synthesis (% / hour; Areta. 2014)

What a brief glance at the data in Figure 2 does tell you, though, is that resistance training will effectively counter, the diet-induced downregulation of the pro-anabolic response to protein. What it won't do, though is to increase the net protein retention to levels comparable to those on an energy balanced diet!

A high protein intake doesn't normalize the levels of anabolic hormones, either | learn more

Loss ￪, synthesis down ￬ ➲ net protein loss - there is no way out! In conjunction with the concomitant reduction in protein synthesis (-27% in the study at hand), the combination of increased loss and decreased synthesis in a caloric deficit will always entail a net loss of protein (also in view of the endocrine deterioration | learn more). What exercise can do for you, though, is to counter the net-reduction in protein synthesis, i.e. maximize the amount of amino acids that is pumped into the muscle, before it's used for hepatic gluconeogenesis.

Contrary to what Areta et al. may have suspected the restoration of the protein synthetic response in the post-workout period did not restore the expression of the amino acid transporter gene SLC7A5 to normal. It is thus not surprising that...

Highly suggested read: " Evidence From the Metabolic Ward: 1.6-2.4g/kg Protein Turn Short Term Weight Loss Intervention into a Fat Loss Diet" | more

"[...] despite this elevation, exercise merely restored MPS [muscle protein synthesis] to a level that was similar to, but not exceeding, rates measured in EB [energy balance]. Accordingly, it appears the metabolic status of the muscle during short-term (5 days) ED [energy deficit] plus a ~10 h fast may dictate that contractile overload in isolation is not enough to increase MPS to values that otherwise would be observed when subjects are in EB." (Areta. 2014)

The results of this recent study do thus have to regarded as another nail an already boarded up coffin that's loaded with bro-scientific myths about "body recompositioning."

A word on "body recomposition": You cannot build muscle, while you are dieting. You can, however improve your body composition by losing more fat than muscle. In the mirror / on photos, the results will look like "gains" - in spite of the fact that you simply revealed the muscle that has always been hidden beneath the blubber.

Unlike the non-existent changes in amino acid transporter expression, the observation that 30g of protein are more effective than 15g will probably not come as a surprise to you - notwithstanding the fac t that this was "the first [study] to determine the acute muscle anabolic response to resistance exercise with two different doses of protein ingested after exercise during short-term ED", by the way. About as unsurprising as the researchers' (eventually unwarranted - I don't see a 20g protein group, here ;-) conclusion that their ...

"[...]results suggest that the optimal amount of protein to maximize the response to a single bout of resistance training while in ED may be above the level (20 g) found to maximize MPS post-exercise for individuals who are in EB." (Areta. 2014)

And my recommendation, not to worry too much about all the details. There are a couple of simple principles that have been working for generations of athletes thriving to cut weight without having to sacrifice muscle mass; and as you should know if you've read and memorized the "9 Simple Rules Every Dieter Must Follow" (go back) consuming 30g of protein with every meal and lifting heavy objects are both part of a set of rules that's rooted in bro- and supported by pro-science.

"There is Such a Thing As Over- training, Beware! When IGF-1 & Co Plummet and MAFbx Gnaws Away Your Muscles, It'll Be Too Late to Acknowledge" | more

Bottom line: In the end, the results of this study are probably less exciting than the title, i.e. "Reduced resting skeletal muscle protein synthesis is rescued by resistance exercise and protein ingestion following short-term energy deficit" may have suggested.

That's yet not the least owed to the fact that you all know what it takes to maximize lean mass retention. If there wasn't that irrational hope somewhere deep inside your head that there was a hitherto unknown non-pharmacological way to build muscle and lose body fat at the same time, you'd now be hitting the weights or enjoying your post-workout protein shake... ;-)

Reference: 

• Areta, José L., et al. "Reduced resting skeletal muscle protein synthesis is rescued by resistance exercise and protein ingestion following short-term energy deficit." American journal of physiology. Endocrinology and metabolism (2014). Ahead of Print.
• Ferrando, Arny A., Doug Paddon-Jones, and Robert R. Wolfe. "Alterations in protein metabolism during space flight and inactivity." Nutrition 18.10 (2002): 837-841.
• Gumucio, Jonathan P., and Christopher L. Mendias. "Atrogin-1, MuRF-1, and sarcopenia." Endocrine 43.1 (2013): 12-21.

Protein Intake & Muscle Catabolism: Fasting Gnaws on Your Muscle Tissue and Abundance Causes Wastefulness

How much of the protein you can eat and how much of it you need two keep the status quo are very different questions.

Don't worry, this article is not about the notorious "Anabolic Barndoor" or the purported magic of "nutrient timing" and post.workout supplements. The thing I want to discuss in today's SuppVersity article is of a more general nature and revolves around the upregulation of the ubiquinase enzymes and consequent proteolysis (=catabolims) of skeletal muscle tissue ... or if you want to use my buddy Carl Lanore's term: "The loss of metabolic currency" we all know you better avoid at all costs, if you care about aging healthily. 

You can learn more about protein intake at the SuppVersity

Are You Protein Wheysting?

Cod protein for recovery

Protein requ. of athletes

High EAA protein for fat loss

Fast vs. slow protein

Too much ado about protein?

What we are going to deal with today is protein breakdown, or the purported general anticatabolic effect of high protein diets. To this ends, we will be taking a closer look at the ubiquitin proteasome system (UPS) response to constant energy deficits (ED) at varied dietary protein intakes before and after the consumption of a high protein meal replacement. An issue, by the way, that was also addressed in a paper that has been published a couple of days ago in the peer-reviewed scientific journal FASEB (Carbone. 2013).

No, this is not a deja vue! You've actually read about the same experiment, yet a different portion of the results back in June, in one of my previous articles on optimal protein intake / supplementation | read more 

In said paper by scientists from the School of Health Sciences at the Eastern Michigan University, the Nutrition Division at the U.S. Army Research Institute of Environmental Medicine, the Human Nutrition Research Center that's located at the U.S. Department of Agriculture, and the School of Medicine and Health Sciences at the University of North Dakota thirty-nine young, fit and healthy adult volunteers, who were caged in a metabolic ward, were randomized to one out of three groups with different baseline protein intakes:

• 0.8g/kg body weight of protein (RDA)
• 1.6g/kg body weight (2 -RDA), or 
• 2.4g/kg body weight (3 -RDA)

The participants, 32 men and 7 women, had to be between the ages of 18 and 42 yr and of stable weight ( 2 kg for a period of 2 mo), to have a body mass index (BMI) between 22 and 29 kg/m²,
and to be physically fit [peak oxygen intake (Vo2peak) 40–60 ml/(kg ·min)].

The subjects followed the prescribed dietary protocol for a whole month (31 days), went into a tightly controlled 10-day weight maintenance phase and started fasting for 21 days, immediately thereafter (Note: To keep the protein intake stable, the dietitians who planned and prepared the meals for all study participants had to prepare meals with a significantly higher relative protein content),

In this study: 30% energy restriction +10% physical activity = "fasting"

Just to avoid any confusions: The above, i.e. a 30% reduction in energy intake and a 10% increase in physical activity, is what John W. Carbone and his colleagues talk about, when they use the word "fasting". It does not mean that the subjects have been sitting in one of those tents, where you can actually measure the energy expenditure for 21-days eating nothing, but their finger and toe nails.

An important note on the accuracy of calculated: While Carbone et al. state that their -30% intake, +10% expenditure protocol will produce an energy deficit of 40%, I'd hope that you as seasoned SuppVersity students see through the futility of calculations like these and let go off figures that signify a degree of exactness that's simply not there.

In view of the fact that the term "fast" is contemporarily used to designate "diets" that are really low in energy (up to ZERO calories, intermittently), I suspect I should also mention that I personally would call the last 21 days of the study the "diet" not "fasting" phase.I mean, 30% reduced energy intake and +10% physical activity? We all know that the health and physique 90% of our fellow men and women would benefit from this regimen.

Muscle biopsies and enzyme expressions

The scientists took muscle biopsies before (fasted) and 2h after (fed) the ingestion of "a commercial nutrition supplement (Boost; Nestlé HealthCare Nutrition, Florham Park, NJ, USA)" with a total energy content of 480 kcal and 20 g of protein to assess the degree of intracellular proteolysis on day 10, i.e. right before the "fast", and day 31, i.e. right after the "fast", of which Carbone et al. write that it was based on individualized menus that were administered under supervision, to ensure compliance.

"To maintain fitness, the volunteers performed resistance type physical activity 3 d/wk, and daily endurance-type exercise, at levels comparable to those they had reported in their prestudy activity logs. To minimize the potential that an unaccustomed training stimulus would influence skeletal muscle outcomes and to ensure accuracy, research personnel closely controlled and monitored the intensity and volume of physical activity. For resistance-type exercise, the volunteers performed 1 single-joint movement per major muscle group (3 sets of 15 repetitions), using workloads determined during the prestudy period. The intensity of the endurance-type activity (40 – 60% VO2peak) was based on prestudy measurements, and verified by indirect calorimetry (ParvoMedics) and the corresponding heart rate during familiarization trials conducted before the study, and by the heart rate reserve-method throughout the interventio." (Carbone. 2013)

The 10% increase in physical activity was achieved by an increase in the length of the daily endurance training sessions that would accommodate for the corresponding increase in energy expenditure

Figure 1: Changes in lean body mass and fat mass (kg) that occured during the 21-days on 40% energy restricted diets with varying amounts of dietary protein in it (based on Pasiakos. 2013)

As you can see in Figure 1, which is based on results the researchers presented in a previous publication that was likewise discussed, here at the SuppVersity, this intervention was not without consequences on the body and fat mass of the study participants who lost on average 3.2 ± 0.2 kg body mass, but at very different lean:fat-mass ratio (learn more).

What's the more important "-bolism": Cata- or ana-bolism?

In contrast to their previous paper that focused exclusively on the increase in muscle protein synthesis, this "follow up"* discards the influx of dietary protein into the muscle of the subjects and focuses on the proteolytic enzymatic response to the diet  (*I assume both were filed at the same time, but the one in FASEB was published ahead of print, while the one at hand did not).

Figure 2: Enzymatic activities for 26S 1(A), 26S 2(B), 26S 5(C), and caspase-3 (D). Open bars, weight maintenance; solid bars, energy restriction.

Put differently, instead of asking the likewise important question: "What's more anabolic?" that was already answered in the paper by Pasiakos et al. (read more). Carbone et al. focus on the similarly or even more important question: "What's more catabolic?" - with a quite intriguing outcome, if I may say.

I mean, you would expect that the activity of the catabolic enzymes would vary depending on the protein content of the diets, wouldn't you? No? Well, maybe you did expect that the response to the 20g protein shake the subjects consumed would have an effect on their expression (black bars in Figure 2)?

You didn't? Tthat's awesome, you must be a genius, 'cause nothing of that actually happened. In other words, the expression of proteolytic enzymes did not in any way or form depend on the total amount of protein, the healthy young subjects in the study at hand consumed on a daily basis - once, twice or thrice the RDA of 0.8g/kg body weight.

Take home message #1 -- Your daily total protein intake has no effect on the expression of catabolic enzymes in your musculature. Even your total energy intake has little effect on the expression of catabolic enzymes in your musculature.

And if we are honest, most of us would probably also have expected a much more pronounced difference in these markers of muscle catabolism, when comparing the weight maintenance to the fasting phase (white vs. black bars) - a difference that existed for some yet not all of the ubiquinase enzymes, but was statistically significant for none of them.

Figure 3: mRNA expression of the Ub ligases MuRF1, atrogin-1 and TNF-alpha (Carbone. 2013)

And just in case you find all that not yet surprising enough, I'd suggest you take a parting look at the Murf-1 and atrogin-1 expression in Figure 3 -- what do you see? Correct, Murf-1 and atrogin-1 are the most prominent members of muscle-specific proteases that are highly expressed during muscle atrophy (Gomes. 2001; Witt. 2005); and you are also correct, if you are now scratching your head thinking:

"But how come that both are increased with higher protein intakes?"

Actually you know the answer already. It's after all not just take home message #2 of today's SuppVersity article, but has been addressed in many previous articles on total protein intake and the effects of protein supplementation here at the SuppVersity, as well.

Take home message #2 -- The more protein you eat the more wasteful your body will be (note: this does not mean that the net protein retention does not increase, but it means that you will see diminishing at intakes of thrice the RDA even non-existent returns; cf. "Are you Protein Wheysting?")

So what's left do discuss then? Ah, right, aside from the proteolytic enzymes, the scientists also tested for changes in the expression of TNF-alpha & co and observed that the expression of TNF- mRNA and activation of NF- B1 increased as protein intake exceeded the RDA.

This increase in TNF-alpha and NF-B1 may at first surprise you - TNF [tumor necrosis factor] and consequent NF- B activation are, after all, generally associated with increased muscle proteolysis. If you look back at "take home message #2", however, you'll realize that this, i.e. an increase in muscle proteolysis is exactly what's going on, in the 2x and 3x RDA groups. It is thus also logical that this increase in tumor necrosis factor occurs only in the fed state - a state, when dietary protein is abundantly available.

So what's to be learned on the practical side of things, then? In view of the results of the study at hand, it appears as if we may in fact have overrated the influence of the loss of skeletal muscle protein, i.e. proteolysis, in the past. Compared to the amplitude, or differences between ups and downs of protein synthesis the activity of the proteolytic enzymes is (a) very constant and does (b) depend inversely, but non-linearly on the total amount of protein you eat.

Remember the recent article about the myostatin reducing and thus potentially muscle building effects of low protein diets? | read more

Practically speaking this means that there is a relatively low threshold beyond which the "loss" of protein (=protein not being incorporated into the muscle tissue) keeps increasing, while the storage of protein stagnates. A hypothesis that stands in line with the results of experiments that investigated the differential effects of bolus (=all at once) vs. staggered (=in 4x20g or 8x10g) ingestion of protein supplements (see "Slow or Fast, Bolus or Pulse? Protein Synthetic Response is Identical!" | read more) and the revelation that protein fasting can decrease the expression of myostatin and thus ramp up the capacity for and efficacy of muscular protein storage (see "36% Decrease In Myostatin, With Low Protein (0.1g/kg BW) Diet" | read more).

References:

• Carbone, J. W., Margolis, L. M., McClung, J. P., Cao, J. J., Murphy, N. E., Sauter, E. R., ... & Pasiakos, S. M. (2013). Effects of energy deficit, dietary protein, and feeding on intracellular regulators of skeletal muscle proteolysis. The FASEB Journal, 27(12), 5104-5111.
• Gomes, M. D., Lecker, S. H., Jagoe, R. T., Navon, A., & Goldberg, A. L. (2001). Atrogin-1, a muscle-specific F-box protein highly expressed during muscle atrophy. Proceedings of the National Academy of Sciences, 98(25), 14440-14445.
• Pasiakos SM, Cao JJ, Margolis LM, Sauter ER, Whigham LD, McClung JP, Rood JC, Carbone JW, Combs GF Jr, Young AJ. Effects of high-protein diets on fat-free mass and muscle protein synthesis following weight loss: a randomized controlled trial. FASEB J. 2013 Jun 5. [Epub ahead of print].
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