Now, almost a year later, Lucilla D. Monti et al. have published yet another paper on l-arginine in the latest issue of the scientific journal Metabolism (Monti. 2013). "A pilot study in healthy subjects and a cross-over study in subjects with impaired glucose tolerance and metabolic syndrome" as the title tells us and reason enough for me to take another look at an amino acid that has gotten sort of a bad rep as a supplemental non-starter, because the marketing machinery of the bodybuilding supplement producer has been pimping it as an "nitric oxide (NO) booster" (which is similar to saying that bricks were 'house builders' by the way).
Arginine cookies the saviors of the human race!?
Just so there is no misunderstanding here, while arginine may be more useful as a weight loss tool (esp. for the insulin resistant), it is neither an NO booster, nor a fat burner in the sense that it would "actively" do anything to elicit the named effects. The additional 4cm the arginine stripped off the waists of the initially mentioned ~28-44year-old women, for example, occurred in the context of a diet containing 500kcal less than the baseline diet (that's about -20% and the average subject ended up eating ~2000kcal/day).
"increases mammalian BAT growth and development via mechanisms involving gene expression, nitric oxide signaling, and protein synthesis [, so that t]his enhances the oxidation of energy substrates and, thus, reduces white fat accretion in the body." (Wu. 2012)Usually I would discard these effects as "most likely irrelevant for virtually BAT free mammals" like humans (even those among us with a "high" amount of brown adipose tissue have way less of it than the average "mammal" does; this is particularly true if you compare us to our small hairy mammalian brethren that are living in lab cages ;-).
With the positive effects that have already been observed in past human studies and the "growth promoting effect" arginine is supposed to have on mammalian brown adipose tissue (cf. figure 1), the potential weight loss and ensuing health benefits of the "conditionally essential" (meaning you must consume it in significant amounts under certain circumstances, like bein very sick, burned, hurt, etc. though your body can theoretically produce it on its own) amino acid appear to be well-worth being mentioned in a SuppVersity article again (again, because I already mentioned these effects as an aside in Part II of the Amino Acids for Super Humans Series back in 2011.
Back to the cookies then
After this lengthy general introduction, let's now finally have a look at the Monti study (Monti. 2013). Now, despite the auspicious term "pilot study" in the title of the Italian researcher latest paper, the idea to add some l-arginine to cookies, biscuits and other stuff is actually not really new. In 2011, already, he same research group has published a paper on this concept with initial data on the acute response to the ingestion of arginine enriched biscuits (see previous SuppVersity post). So, the "pilot trial" is actually nothing but a slightly revamped version of the initial test in 7 healthy subjects, plus a 2-week extension in which the scientists probed the effects of the chronic ingestion of their biscuits on 15 obese subjects (8 men, 7 women, aged 62.5±3.5years; BMI ~30kg/m²; 36% body fat) with impaired glucose tolerance (IGT) and metabolic syndrome (MS).
|Figure 2: Weight loss, fat loss and insulin sensitivity (*I divided the actual values on the Matsuda index by 10 so that they would fit into the same graph), as well as glucose response during an OGGT (Monti. 2013)|
During each of the two 14-day intervention periods, the obese volunteers had consumed identically packaged L-arginine-enriched biscuits containing 6.6g l-arginine, 21.9g carbohydrates (15g available
carbohydrates and 6.9g resistant starch), 3.6g protein, 7.5g fat or an isoenergetic biscuit without the 6.6g of l-arginine as morning and afternoon snack . The additional 171kcal provided by the biscuits were included in the daily allowance of the subjects who followed a 55% carbohydrate, 25%–30% fat and 15%–20% protein diet that contained a total of 1,600kcal during the whole 6-week study period (the study used a randomized cross over design with a 2-week washout in-between).
Let's get back to a more general perspective
Not just because I'd hope that most of you don't have just as much weight to lose as the participants of the Monti study, but also in view of statements like "[a]nother added value of the biscuit is the low protein content (6.1% vs. 20%–50%)" (Monti. 2013) in the discussion of the paper, I don't want to go into more details on this particular study, but rather return to a more general analysis of the metabolic effects of l-arginine in these last paragraphs. I mean, it should be obvious that the important most important question here is: "Is there any metabolic benefit of arginine supplementation, or not?
The results of the Monti study clearly show that there is (and that despite the fact that its authors' don't appear to have a grasp of the latest research results). Monti's paper does yet not describe the only experiment, the results of which would suggest that there is more to arginine than nitric oxide - or, if we go by the overview in figure 1, that there is more to nitric oxide than the pump.
- In June 2012, researchers from the Poznan University of Medical Sciences in Poland, for example, published a paper in which they report that the provision of 9g/day of the nitric oxide precursor l-arginine for 3-months lead to statistically highly significant improvements in insulin sensitivity and a non-significant 1% reduction in body fat in the absence of any changes in dietary or activity patterns in patients with visceral obesity (BMI 39kg/m²). It did yet not, as the scientists had speculated reduce the expression of tumor necrosis factor alpha (TNF-alpha), so that we have to assume that the beneficial effects on glucose management were not mediated by any hitherto largely ignored direct anti-inflammatory effects of the amino acid the Swiss chemist Ernst Schultze discovered in 1886 (Bogdanski. 2012).
- In the American Journal of Physiology. Endocrinology and Metabolism Lucotti et al. reported in 2006 that the addition of l-arginine (8.3g/day) to a combined diet plus exercise program for 21 days had highly beneficial effects on the study outcome, promoted the loss in fat mass (3kg vs. 2kg) and waist circumference (10cm vs. 3cm; no typo!), helped preserve lean mass (0kg vs. 2kg muscle loss) and improved the mean daily glucose profiles and the amount of fructosamine, a glycated serum protein and marker of poor glucose control, in the blood (Lucotti. 2006). Moreover, the supplementaion protocol increased the nitric oxide production, the andioxidant capacity and the adiponectin levels and improved the adiponectin-to-leptin ratio of the 25 women and 8 men (all obese, BMI ~39kg/m²) who participated in the study.
- In addition, studies on rodents and pigs have conclusively shown that arginine supplementation can increase the use and decrease the storage of fatty acids in different dietary scenarios (Fu. 2005; Jobgen. 2009; Tan. 2011).
Is timing crucial and what about the arginine induced insulin release?
|Maybe it's even it's effect on the health of your intestines (read more about that) that helps weight loss, who knows?|
What we should however keep in mind, though is that a robust initial insulin response will lead to a faster reduction of blood glucose in into the normal range. That it turn will (ideally) render the release of even more insulin obsolete so that the initial spike will actually allow you to avoid the far more detrimental chronically (or in a "healthy" individual "long-term") elevation of insulin and can thus have the bring about the exact opposite of what most people believe it will do: weight loss, or a reduction in weight gain!
"So does it work and if so how? Can't be insulin, alone, can it?"
It is nevertheless unlikely that the increased acute response of the pancreas is the only mechanism (I would bet probably not even the most important one) by which increases in the amount of arginine in the diet facilitate and as examples like the study by Bogdanski et al. (Bogdanski. 2012) even trigger weight loss (remember: the obese subjects in this study did not do anything but take 9g/day of supplemental l-arginine three times a day).
Effects by which arginine could promote fat loss and body recompositioning: Stimulation of lypolysis (release fat from adipose tissue); activation of genes that are responsible for the oxidation of fatty acids; interaction with PGC-1 alpha and triggers mitochondrial biogenesis and the "browning" of fat; regulation of adipocyte-muscle crosstalk resulting in an energy repartitioning effect away from the adipose and towards the muscle tissue; activation of the AMPK pathway, resulting in improvements in both lipid and glucose metabolism.According to a review by Tan et al., both the additive (dieting + arginine = better fat loss), as well as the "stand alone" (simply adding arginine on top of whatever diet you are following) effects of the nitric oxide precursor could be brought about by a combination of various factors (Tan. 2012). We have already seen in figure one that the nitric oxide exerts direct agonistic effects on PPAR-alpha. We also know that other substances such as fish oil and TTA (see "TTA + Fish Oil - Fat Burning Super Fats?"), which are likewise PPAR-alpha agonists will also promote the oxidation of fatty acids (specifically in the liver). Now, if you add the list of metabolic benefits, the scientists from the Institute of Subtropical Agriculture at the Chinese Academy of Sciences in Changsha and their colleagues from the Texas A&M University have compiled (see infobox on the right), you will have to concede that your pre-workout nitric oxide booster would - at least on paper - make a pretty decent "fat burner", if all these effects, most of which have been observed in either rodents or pigs could be replicated in human beings.
Bottom line: For the metabolically deranged, the evidence is there. For followers of physical culture, on the other hand, there is as of yet no clear cut proof for the fat burning or repartitioning effects of l-arginine. Ah, and just in case you consider your little N=1 experiment with whatever pre-workout supplement evidence that it does not work - forget about that. With the minuscule amounts of l-arginine most of these products contain you can hardly make a difference when your basal diet does deliver tons of arginine, already (plus: you were probably taking it at the wrong time, namely on empty before a workout).
So do I suggest you buy a 5kg pouch of bulk l-arginine and go through it within 2 weeks? No, certainly not. You better wait until more data becomes available. For now, it would suffice if you don't fall for the anti-hype that's at least in part instigated by the same supplement companies that have been pimping l-arginine a couple of years ago as the ueber-supplement and an absolute must have for any serious trainee. I mean if you had the choice between six pack abs lasting 24/7 and a pump, what would you pick? I thought so... therefore this new area of application, could turn out to be way more exciting than the never-established, but highly marketed NO-boosting effects of l-arginine.
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