Exogenous amino acids stimulate human muscle anabolism without interfering with response to mixed meal ingestion.
Douglass Paddon-Jones, Melinda Sheffield-Moore, Asle Aarsland, Robert R. Wolfe, and Arny A. Ferrando
Am J Physiol Endocrinol Metab 228: E761-E767, 2005.
ABSTRACT. We sought to determine whether ingestion of a between-meal supplement containing 30 g of carbohydrate and 15 g of essential amino acids (CAA) altered the metabolic response to a nutritionally mixed meal in healthy, recreationally active male volunteers. A control group (CON; n = 6, 38 +/- 8 yr, 86 +/- 10 kg, 179 +/- 3 cm) received a liquid mixed meal [protein, 23.4 +/- 1.0 g (essential amino acids, 14.7 +/- 0.7 g); carbohydrate, 126.6 +/- 4.0 g; fat, 30.3 +/- 2.8 g] every 5 h (0830, 1330, 1830). The experimental group (SUP; n = 7, 36 +/- 10 yr, 87 +/- 12 kg, 180 +/- 3 cm) consumed the same meals but, in addition, were given CAA supplements (1100, 1600, 2100). Net phenylalanine balance (NB) and fractional synthetic rate (FSR) were calculated during a 16-h primed constant infusion of L-[ring-2H5] phenylalanine. Ingestion of a combination of CAA supplements and meals resulted in a greater mixed muscle FSR than ingestion of the meals alone (SUP, 0.099 +/- 0.008; CON, 0.076 +/- 0.005%/h; P < 0.05). Both groups experienced an improvement in NB after the morning (SUP, -2.2 +/- 3.3; CON, -1.5 +/- 3.5 nmol x min(-1) x 100 ml leg volume(-1)) and evening meals (SUP, -9.7 +/- 4.3; CON, -6.7 +/- 4.1 nmol x min(-1) x 100 ml leg volume(-1)). NB after CAA ingestion was significantly greater than after the meals, with values of 40.2 +/- 8.5 nmol x min(-1) x 100 ml leg volume(-1). These data indicate that CAA supplementation produces a greater anabolic effect than ingestion of intact protein but does not interfere with the normal metabolic response to a meal.
Today’s objective is two-fold. The first objective is to outline for everyone how to critically analyze and interpret a scientific paper using a specific example (i.e. the study above). The second objective is to simply give my interpretation of the paper provided and the reasoning behind my interpretation. You are free to disagree, but if so, please provide evidence as to why. That being said, we can now move on.
Today’s paper is not new. In fact, it was published back in 2005 by a group of researchers from the University of Texas and Shriner’s Hospital for Children in Galveston, TX, but I like the topic so much, because amino acids (AA) are becoming such a growing presence in the gym and among athletic communities, alike. This group has put out plenty of other papers on amino acids and muscle protein synthesis and I suggest looking them up and digging through the literature if you’re interested. I will not talk much about those papers because that will not be my focus today, but rather I will analyze this paper and see if their conclusions are sound and if any recommendations can be made from this paper. I will, however, disclose some information right now, being, that anyone who makes a recommendation from one paper is foolish, so essentially no recommendations can be made, however implications can, and even those are shaky without a body of literature. So let’s continue.
As provided above, the abstract is meant to supply the reader with (almost) everything he/she needs to know about the study. There is a brief 1-2 sentence opening describing why the study is important, and it then continues with the methods and procedures, any salient results, and finally their conclusions based off of the results. Simply reading an abstract doesn’t give you all of the information needed, because their might be some methodological flaws or inherit bias built into the study, and therefore the entire text is needed to fully critique and analyze the findings. The above paper is freely available online and I highly suggest finding it and reading along as you read.
The introduction is meant to describe to the reader WHY the paper is important. It may also illuminate some previous research that was done which prompted this study and it may even provide some statistics to show you how important the problem is and why this study is important to help alleviate that problem. Today’s paper does just that. The authors open with the rationale (reasoning) for why AA supplements should be used, and the specific requirements that a supplement must have in order to be effective. They also allude to some previous research which prompted this study to be done. They finish with their objectives for the study, which were to examine the effects of an AA and carbohydrate (CHO) supplement on muscle protein synthesis (MPS) when given between meals. This is essentially only relevant for certain populations looking to maximize muscle gains. A study like this can provide some critical insight into how to treat older populations who are at risk for sarcopenia, which simply means losing muscle as one ages, or in clinical settings where people are in extreme catabolic states and desperately need to hang on to whatever lean tissue they have. The final population is the athletic community who wish to maximize muscle gains. I will essentially be speaking directly to the latter.
Materials and Methods
The next section is probably one of the most important (and potentially boring) sections of the paper. A result is only as good as the method used to produce that result. Remember that. This means that you might get a great result, but if the method (or protocol) used to find that result was poor then those findings come into question. Now, let us use that rationale and apply it to this section of this paper.
The researchers had 13 (n = 13) healthy, physically active males between the ages of 28-48 participate in the 16-hr, in-lab study. Seven (7) of them were assigned to the supplement (SUP) group and the remaining six (6) were the placebo or control (CON) group. The control group is meant to be used almost as a baseline, so that any differences seen between the two groups can be solely attributed to the supplement given to the treatment group. Simply put, every condition is the same for each group EXCEPT the supplement given to the SUP group. Easy enough.
Once admitted to the facility where they would be studied, the participant’s caloric requirements were established using the Harris-Benedict equation (~2,600kcals each). From here, each participant’s total caloric intake was split evenly over 3 mixed-meals (breakfast, lunch, dinner) with 59%, 27%, and 14% of calories coming from CHO, FAT, and PRO, respectively (This means each group got the same percentage of carb, fat and protein given their caloric requirements). This amounted to about 380g CHO, 93g FAT, and 70g PRO for each participant. In addition to the 3 meals, the SUP group was given an AA supplement containing 30g sucrose, and 15g essential amino acids (EAA) dissolved in a diet, calorie-free beverage, regardless of caloric requirements. The CON group received only the diet beverage. The supplement was given after each meal i.e. three times throughout the study protocol to each of the seven SUP group members.
Throughout the study blood samples were taken periodically and a continuous infusion of stable isotope phenylalanine was administered in order to measure muscle protein synthesis (MPS) as well as the rate of that synthesis.
The second most important section of the paper is the results. The results tell you whether or not the experimental condition worked or didn’t work. This either proves or disproves the hypothesis.
The most salient results of this study were as follows:
- The meals plus the EAA+CHO supplement resulted in a greater anabolic response than just the meals alone.
- The rate of MPS in the SUP group was ~25% greater than the CON group.
Simply put, the SUP group had a greater anabolic response from the supplement, and their rate of MPS was greater than the CON group. The rest of the results are listed in the abstract above. I merely listed the most relevant ones to my discussion.
This is the part where the authors take their results and try to explain them. They might also relate their findings to other previous findings that were seen in other studies done elsewhere. This is also the chance for the authors to reflect on the strengths and weaknesses of the paper wherein suggestions can be made for future studies. Sometimes a separate section, conclusions can also be made in the discussion. This is essentially their interpretation of the results which can be accepted or doubted by the reader. Here is where I will give my interpretations of the findings. As I stated earlier, feel free to agree or disagree, but make sure to back it up. I will refer you to my very first post back in January as to why I believe this.
At first glance, one might argue that an amino acid supplement taken in between meals indeed works to enhance MPS and that taking an EAA supplement will surely increase muscle synthesis (especially bodybuilders and muscle-hungry gym-goers that only care about increasing muscle mass). However, let us backtrack and take a look at the study protocols again before we go jumping to conclusions.
First-off, this is a short-term study (16-hrs) and tells us nothing about consistent, long-term AA supplementation.
Secondly, and more importantly, the researchers used protein intakes which are DRASTICALLY lower than what many bodybuilders or other athletes consume on a daily basis. In this study, all participants consumed a paltry 70g of protein/day spread over their 3 meals (~23g per meal). In my opinion, 70g is not sufficient enough protein for the athletic population trying to build muscle, so the results cannot accurately be applied to this population who most definitely do consume enough protein. Furthermore, even with the EAA+ CHO supplement, the SUP group only amounted to 115g total protein which is barely adequate to begin with, which brings me to my next and final point.
The final major flaw of this study was that the SUP group’s total caloric intake, as caused by the supplement, was greater than the CON group due to the extra 45g EAA and 90g of CHO (~540kcals). This amounted to ~2,600kcals for the CON group and ~3,150kcals for the SUP group. Again, the two group’s diet conditions were so different that it’s hard to say that the supplement is what caused the results. It could have just been virtue of eating 500+kcals over the SUP group’s baseline needs. Had the researchers controlled for kcals the study would have been much better. Usually during studies using micronutrients this isn’t an issue because vitamins and minerals do not supply calories. However, this study seemed to neglect controlling for calories, and to me this was the biggest flaw.
In conclusion, the aforementioned are all confounding factors which bring the final results into question. Does this mean that taking an amino acid supplement won’t help increase MPS for the athlete/bodybuilder looking increase his/her muscle mass? Well, it’s hard to say. Given adequate protein intake (definitely one above the intakes seen in the study), adequate calories, and a solid training protocol it’s nearly impossible to argue that this study answers the question at hand. There are just too many confounding factors and weaknesses in the study which make it useless when put into context of the athletic population who most likely cover all their dietary needs to begin with. A much better study would have used adequate protein intakes and would have controlled for calories.
Summing it up
As you can see, it’s not good enough to only read the abstract. There are many components of a research paper besides the results and conclusions. It is up to you to dig through the literature, recognize potential flaws and bias, and make your own decisions given the data. As I just showed you, something may seem great at first glance, but once you start picking it apart and analyzing the details you may realize the results aren’t as applicable or as relevant as you thought. Which brings me back to the insistent and unrelenting theme of my Blog, and that is context. It is IMPERATIVE to keep things in context, because without context, results mean nothing.