Hormones are our body’s method for signaling between cells.  Perhaps this sounds like a boring topic and you may be wondering why I’m discussing them here.  It turns out, this element of biochemistry is of critical importance when we consider things like optimizing diet for a specific set of goals.  Maximizing muscle growth can be achieved through one set of hormonal responses, while optimizing for fat burning requires another set of responses.  So, if we can manipulate hormone response in the body, then we can better achieve body composition goals.  To this end, I recently came across a study that takes a detailed look at hormone response to three unique dietary protocols.


The Study

Twenty-eight males were examined with BMIs ranging from 18 to 24.  These subjects were split into three groups: 1) fed a dose of essential amino acids (AA group), 2) iso-caloric control group (IC group) and 3) fasted control group.  Each group was fed their respective diet upon completing an overnight fast.  Once fed, various hormones were monitored across all individuals at regular intervals for a 5 hour period.


The amino acid group was fed 0.35g per kg of bodyweight of an AA mixture.  The IC group was fed a skimmed milk powder solution containing 36g protein, 52g carbohydrates and 1g fat (the naming of this group is a bit curious since iso-caloric is typically used to indicate equal parts of each macronutrient).  Finally, the fasted group should be self explanatory, they continued their overnight fast for the duration of the experiment.

The objective of the study was to better understand anabolic and catabolic pathways in response to dietary inputs.  Accordingly, the hormones monitored were: insulin, hGH, ghrelin, leptin and cortisol.  I’d love to get into the nitty gritty about each of these hormones, but that’d turn this post into a novel, so I’ll just provide a quick blurb about each and then discuss the bigger picture for the three dietary groups.


Hormone Response

Insulin is an anabolic hormone that simultaneously stimulates the growth of both muscle and fat tissues.  In both the amino acid group and the iso-caloric group, insulin was secreted rapidly, peaking 20 minutes after consumption.  Levels remained unchanged in the fasted group.

hGHGrowth Hormone (or hGH) is likely familiar to many people.  The artificial form is infamously known as a supplement used by athletes looking for an edge over their competition.  hGH is well established as an anabolic agent in the body.  In addition to the artificial formulation, hGH is also produced naturally.  This hormone exhibited the greatest variability across the three test groups.  Interestingly, there was a massive spike in hGH in the AA group, while levels in the IC group held steady and the fasted group saw a small, but steady rise throughout the experiment.  During the spike for the AA group, the authors observed a great deal of variability amongst participants within this group.  They speculate that personal factors such as age, training status, etc. greatly influence the magnitude of hGH response.

Cortisol is often referred to as the stress hormone and can elicit a catabolic response in the body.  Elevated levels of cortisol can lead to muscle break down through a process known as proteolysis.  The AA group saw a decline in cortisol levels while the other two groups saw no statistically significant changes in this hormone.

Leptin helps to regulate hunger (as I discussed recently).  No changes were seen in leptin levels for any of the groups.  It actually came as a surprise to the authors that there wasn’t a change for the fasted group in response to their lack of caloric input.  Ultimately, they concluded that the 5 hour window over which they observed participants was insufficient to see changes in this hormone.

Ghrelin is known to have the opposite effect of Leptin, in that it induces hunger.  There was a dramatic increase of this hormone in the AA group and a slight uptick in the fasted control group.  Levels in the IC group remained constant.  In addition to signaling hunger, ghrelin is known to have a growth hormone releasing function which is consistent with the hGH response observed in each of the groups.


What does is it all Mean?

Ok, let’s look at these responses by study group now to get a handle on the bigger picture.

First, the amino acid group, experienced an uptick in insulin, hGH and ghrelin. These 3 hormones are anabolic in nature.  Meanwhile, this group saw a decrease or no change in cortisol and leptin – the catabolic signalers considered in this study.  Simultaneous stimulation of anabolic pathways and depression of catabolic ones pushes the body into a state of net anabolism.  So, at least for the 5 hour period observed during this study, this regimen is highly anabolic and should be considered by those looking for big mass increases.

muscle-growthPerhaps, at this point, you’re all pumped up to begin an AA protocol.  Well, keep in mind that hormones like insulin (typically) stimulate growth equally in muscle and fat tissue.  The hormonal response of the fasted group demonstrates many interesting properties for those looking to lean out.  It is a common misconception that fasting stimulates catabolic pathways.  Fasted participants in this study exhibited an increase in hGH with no changes to catabolic signalers cortisol and leptin.  These findings are consistent with the claims of the intermittent fasting crowd.

What about the iso-caloric group?  All hormone levels remained unchanged except that of insulin.  Insulin is anabolic, though as mentioned above, it blindly stimulates growth in all tissue, including fat.  Interestingly, this diet closely mimics a typical American breakfast, high in carbohydrates, low in dietary fat.  Is it any surprise that obesity levels are on the rise?



For those of you that got bored and wanted a concise interpretation of the study findings, here you go….  If you’re looking to bulk up and don’t mind adding a little fat with a lot of muscle mass, the amino acid protocol is perfect for you.  Those of you looking to increase muscle mass, albeit at a slower rate, but continue to lose fat mass, consider fasting through the mornings.  Finally, those of you that want to become big fat, fattys, continue to crush breakfasts high in carbohydrates.



Endocrine responses to the oral ingestion of a physiological dose of essential amino acids in humans.  Gröschl M, Knerr I, Topf HG, Schmid P, Rascher W, Rauh M.  J Endocrinol. 2003 Nov;179(2):237-44.