Update on maximal anabolic response to dietary protein.The anabolic response to dietary protein can be defined as the difference between protein synthesis and breakdown, or the net protein balance, in response to ingestion of protein alone or a mixed meal containing protein. However, this concept was based entirely on the measurement of muscle protein synthesis and thus ignored the potential contributions of suppression of protein breakdown to the anabolic response, as well tailbone pain after steroid injection the possibility that tissues and organs other than muscle may also play anabllic role in the anabolic response. In this review we discuss protein anabolic factors comprising the total anabolic response, discuss relevant methodological issues, qnabolic a theoretical protein anabolic anabolic response based on current literature values, and interpret recent papers addressing the issue of maximal anabolic response as well as meal distribution of dietary protein. We conclude that it is not protein anabolic that there is a practical protein anabolic to ananolic maximal anabolic response protfin a single meal, and the most efficient way in which to maximize the total anabolic response over a h period is to increase dietary protein at breakfast and lunch without reducing protein intake with dinner. Essential amino protein anabolic Muscle protein synthesis; Optimal protein intake; Protein intake pattern; Protein quality. National Center for Biotechnology Protein anabolicU.
Update on maximal anabolic response to dietary protein. - PubMed - NCBI
Given that the main focus of many physique competitors and athletes alike is to improve their body composition , muscular hypertrophy and fat loss are often their primary concerns. Therefore, it seems prudent to cover the basics of what exactly anabolism and catabolism mean in these respects.
This guide is intended to cover the major factors of the human endocrine system and their role in protein anabolism and catabolism. Metabolism is one of those terms that pretty much everyone knows and uses but yet few actually understand, so this section will serve to give you an elementary grasp of what exactly metabolism is. All living organisms are made up of the simplest living unit—the cell. Back to the concern at hand, within these cells chemical reactions are constantly occurring while utilizing and giving off energy in the process.
These reactions are divided into two classes that we alluded to in the introduction, those being anabolic and catabolic; the former use energy to build cell components and molecules while the latter give off energy as they break down complex substrates. Therefore, when we speak of metabolism, we are referring to the summation of all of these physiological reactions within the cell that are necessary to sustain life. A multitude of variables such as hormone signaling, physical activity, nutrient availability and energy status affects how these reactions occur and when they take place.
Anabolic reactions serve to build cellular components and molecules while catabolic reactions do the opposite. The goal of most any individual in the gym is to improve their body composition i.
The conundrum is that improving body composition is a give and take process. In bodybuilding and fitness subculture many people become obsessed with the idea of simultaneously losing fat and building muscle. However, these events are theoretically mutually exclusive as one scenario requires an energetic deficit and the other requires an energetic surplus. So one way to think of improving body composition is like a see-saw between building muscle and losing fat—if you want to increase one then the other will have to decrease.
Skeletal muscle tissue serves as the largest reservoir of amino acids in the human body. However, many people misconstrue the message being sent when someone refers to protein synthesis. Proteins are essential macromolecules that play a myriad of roles in humans; they are not solely relegated to muscle tissue and in fact are quite ubiquitous throughout many body systems:. Before moving on, hopefully those of you who get a bit confused with all the technical jargon will benefit from this quick overview of some terms that will be used throughout this guide:.
Okay, so now we have arrived at the meat and potatoes of this guide and will get into what factors play a large role in protein anabolism and catabolism, which ultimately has ramifications on body composition. As alluded to earlier, anabolic reactions serve to build cellular components and molecules while catabolic reactions do the opposite. Also recall that anabolic reactions require energy input and catabolic reactions give off energy. So we will breakdown how protein anabolic and catabolic reactions play a role with regards to building skeletal muscle tissue—one of the most pertinent components to improving body composition.
Bear in mind that many of the hormones and factors discussed in this guide have a certain amount of interplay among one another so it is nearly impossible, if not impractical, to isolate these components especially in everyday settings.
As noted earlier, skeletal muscle tissue serves as the largest reservoir of amino acids in the body and makes up the largest mass of protein. There are essentially two amino acids pools we are concerned with here—the circulating pool and intracellular pool.
When the body is in a state of starvation and other catabolic instances , amino acids are released from muscle tissue into circulation and utilized by other body tissues. On the contrary, when protein anabolism is necessary, amino acids can be actively transported from circulation into the intracellular space of muscle cells and incorporated into proteins thus synthesizing new protein.
In animals mainly carnivores amino acids provide a generous amount of energy from the oxidation of amino acids. Ammonia is excreted as urea via the kidneys in humans, while the carbon skeletons of amino acids enter the citric acid cycle for production of energy. Estrogens increase systemic GH levels and paracrine IGF-1, both of those being a favorable characteristic for protein anabolism and anti-catabolism. Insulin is a peptide hormone secreted in the pancreas of humans mainly in response to elevations in blood sugar levels since it acts as an up-regulator of glucose transport proteins.
With the onset of a dramatic increase in type-2 diabetes in the United States, insulin has unfortunately found itself being cast down as the enemy of human physiology as we know it. Insulin is one of the most potent anabolic hormones in the human body and acts to induce protein anabolism in the entire body when amino acids are replenished.
Moreover, while insulin does reduce whole-body protein breakdown, it does not modulate the ubiquitin system that is responsible for regulation of muscle protein breakdown. Therefore, insulin is not a specific reducer of muscle protein breakdown.
This suggests that a state of hyperinsulinemia paralleled with a state of hyperaminoacidemia elevated plasma amino acid levels should be quite conducive to facilitating muscle protein synthesis.
This is in fact why patients in a state of critical cachexia are often setup with an infusion of amino acids and insulin. All the scientific mumbo jumbo can sometimes cause us to lose sight of the bigger picture. The take-home message is that insulin is indeed a highly anabolic hormone that is conducive to skeletal muscle protein synthesis but that an exogenous source of amino acids is necessary to create this effect.
As noted above, a state of hyperinsulinemia and hyperaminoacidemia will facilitate muscle protein synthesis, and what better way to induce such a state then by simply ingesting protein and carbohydrates.
Many people believe that a superfluous rush of fast-acting carbohydrates along with whey protein is ideal, especially after weight training to maximize the muscle protein synthetic response.
As you may have likely derived from the nomenclature, IGF-1 is a peptide hormone quite similar in molecular structure to insulin that has implications on the growth of humans. IGF-1 is produced mainly in the liver upon binding of growth hormone GH and acts either locally on select tissues paracrine or systemically endocrine ; thus, IGF-1 is a mediator of the effects of GH.
IGF-1 is a potent initiator of the AKT signaling pathway in cells, which has ramifications on cell growth and proliferation. In recent years some supplement companies have tried to make the claim that deer antler velvet extracts are conducive to skeletal muscle growth and healing in humans due to the potent amount of IGF-1 contained in said extracts. GH is a peptide hormone produced in the pituitary gland that stimulates cellular growth and reproduction.
When subjects are well nourished, GH stimulates production of insulin from the pancreas and IGF-1 once it reaches the liver which subsequently promotes growth of lean body mass, adipose tissue, and storage of glucose. During fasting and other catabolic states, GH predominantly stimulates the release and oxidation of free fatty acids for use as energy, thus preserving lean body mass and glycogen stores.
GH does indeed have a variety of anabolic actions in the human body, but they are mechanistically different from those of insulin. GH may be viewed as the primary anabolic hormone during stress and fasting, whereas insulin is the major anabolic hormone in the periprandial timeframe.
Research has shown that GH strongly inhibits amino acid oxidation recall from earlier that amino acids may be oxidized for energy.
Thus, GH acts to spare crucial amino acids in the amino acid pools, resulting in a greater availability of those amino acids for incorporation into proteins.
That being said, it appears that GH is a promoter of whole-body protein synthesis in the short-term and any increases in muscle protein synthesis from GH administration are likely the result of downstream paracrine local IGF-1 release.
Both GH and testosterone which we will cover later in this guide increase paracrine IGF-1 which could be of benefit for anabolic effects in skeletal muscle tissue. A curious finding is that in studies that give subjects exogenous doses of IGF-1, the expression of paracrine IGF-1 is suppressed and thus no increase in muscle protein synthesis is observed. It has been shown that GH not only promotes protein synthesis but also inhibits protein degradation, and it is likely that this effect is seen in skeletal muscle tissue due to paracrine expression IGF A final point to consider with regards to the anabolic actions of GH is that it accelerates the transport of several essential amino acids across the cell membrane, specifically those mediated by System L—the major transport system responsible for sodium-independent transport of neutral amino acids such as leucine, isoleucine and valine.
To recap, GH is a potent hormone that promotes whole-body protein synthesis and decreases whole-body protein breakdown, and it is likely that those effects could be induced in skeletal muscle tissue as well once the downstream production of paracrine IGF-1 kicks in hopefully more research will be directed towards this concern in the coming years. GH also strongly inhibits the oxidation, and increases the transmembrane transport, of important amino acids such as the branched-chain amino acids leucine, isoleucine and valine.
Also of note is that GH is a major influencer on fat loss since it promotes the use of free fatty acids for energy. As was noted in the above IGF-1 section, a variety of factors play into when and how much GH is secreted. One way to think of the improving body composition is like a see-saw between building muscle and losing fat—if you want to increase one then the other will have to decrease.
Many readers are likely familiar with the term anabolic androgenic steroid AAS that is often used in the media and fitness subculture. That right there tells you that androgens are indeed anabolic hormones, and they influence the development and maintenance of male sex organs and secondary sex characteristics.
There is a significant body of evidence that shows testosterone plays a pivotal role in the growth and maintenance of skeletal muscle tissue. In studies administering hypogonadal men a replacement dose of testosterone, fat-free mass, skeletal muscle strength, and muscle protein synthesis all increase rather dramatically. It appears that mechanistically testosterone, similarly to GH, exerts part of its anabolic effects by decreasing amino acid oxidation specifically leucine and increasing their uptake into whole-body and skeletal muscle proteins.
Furthermore, there appears to be a synergistic but independent anabolic effect between testosterone and GH, enhancing their benefits on skeletal muscle protein synthesis. Testosterone is a strong inhibitor of amino acid oxidation and increases whole-body and skeletal muscle protein synthesis and also appears to have anti-proteolytic effects. Estrogens are quite plainly the principal female sex hormones and responsible for growth and maturation of female reproductive tissues, but they are still present in males albeit at much lower concentrations.
There are three major estrogens produced in the steroidogenesis pathway of humans: Estradiol, on a molar basis, is about 10 times more potent than estrone and 80 times more potent that estriol with respect to its estrogenic effects.
In females, most estrogens are produced in the ovaries via aromatization of androstenedione, while in males it is produced in small amounts in the testes and more so from aromatization of testosterone in fat cells.
Studies have shown that estrogens increase systemic GH levels and paracrine IGF-1, both of those being a favorable characteristic for protein anabolism and anti-catabolism. However, when excessive estrogen is present it can be indirectly catabolic by blockading androgen receptors and down-regulating the production of gonadotropin-releasing hormone in the hypothalamus ultimately lowering the production of testosterone in the body.
Like with many other things in the health and fitness world, there is a balance to be found when it comes to your estrogen levels. Just be cautious as excess estrogen levels especially in males will likely decrease testosterone production and availability, thereby impeding the positive effects of testosterone on protein metabolism. Thyroid hormones are a major regulator of metabolic rate and affect nearly every cell in the human body.
The thyroid gland gland produces thyroxine T4 and triiodothyronine T3 , with T4 being the prohormone of T3. Research seems to suggest that thyroid hormones increase both whole-body protein synthesis and degradation, but more so the latter than the former, resulting in a net catabolic effect on whole-body protein metabolism. The primary glucocorticoid produced in humans is the stress hormone cortisol. Cortisol is an essential hormone necessary to sustain life, but like with many other hormones, too much or too little of it can wreak havoc on the body.
Often times this comes at the cost of degrading proteins in order to utilize amino acids as a substrate for the gluconeogenic process. Glucagon is a peptide hormone produced in the pancreas that functions basically in reverse to insulin e. Similarly to cortisol, glucagon influences gluconeogenesis and also glycogenolysis. This hormone is produced in the central nervous system and adrenal glands and acts on pretty much all tissues in the body by binding adrenergic receptors.
As with cortisol and glucagon, epinephrine stimulates glycogenolysis in the liver and muscle. Protein synthesis rates in skeletal muscle tissue appear to decrease somewhat dramatically in response to stress hormone infusions.
Also of note is that epinephrine and cortisol may inhibit insulin secretion, and recall from earlier that insulin is an anabolic hormone. Some research also suggests that cortisol blunts the synthesis of paracrine IGF-1, which as aforementioned would be counterproductive to the goal of protein anabolism. The data does seem to show that infusions of these hormones promote protein breakdown in most tissues throughout the body and stimulates the oxidation of amino acids.
They may also impair protein synthesis after chronic exposure and blunt the release of insulin and paracrine IGF Ultimately the summation of these actions results in a net catabolic effect.
Unless you have abnormally high cortisol, glucagon and epinephrine concentrations in the blood for prolonged periods of time e. While this guide is fairly rife with scientific jargon, I hope it serves readers with an understandable overview of some major factors that affect protein metabolism. The options laid out in this guide to modulate the levels of some of these hormones are all meant to act via endogenous production, not exogenous administration.
It is always imperative that we take into account circumstances and the context of the situation at hand. It is impractical, and ill-advised, to discount individual variables that come into play when offering someone advice with regards to their diet, nutrition and training.