Hormonal & Appetite Response to Macronutrients

I came across this paper recently and thought I would share it here on my blog.  I think it is rather eye-opening as to the postprandial hormone responses to meals rich in each of the macros (and alcohol) and the ultimate effect on satiety.

Meals with similar energy densities but rich in protein, fat, carbohydrate, or alcohol have different effects on energy expenditure and substrate metabolism but not on appetite and energy intake

This study was done in normal weight healthy humans (9 women, 10 men) in their early 20's.  They fed them a meal containing the same calories, but high in one of each nutrient.  Each subject was given each diet with a 4-8 week "washout" in between, a standard diet the day before each test day, and subjects fasted 10 hour overnight before testing.   Hormones, etc. were measured for 5 hours postprandially, and then were provided an ad libitum meal.   Here are the diets tested:

Unfortunately it would be impossible to keep all things constant varying so many parameters, but the high protein meal contained roughly 2.5X the 12% for all of the other meals.  The high carb v. high fat meals were relatively isoprotein with fat/carb percents flipping between the two meals at 65% for the enriched macro.  In the alcohol meal they essentially exchanged 23% of carb calories for alcohol.  

Below are some subjective assessments related to appetite and satiety.  Interesting, eh?  Apparently none of the differences reached statistical significance, but *if anything* they trended in favor of protein and carbs over fat.  It's interesting as well that the ad libitum intake was significantly different between men and women.  If anything, both fat and carb reduced future intake in the women but increased it in the men (not stat.sig., just trends folks).  

This next graphic at left is for blood glucose and lactate along with insulin and glucagon profiles.   At right of each are the "AUC's" indicating total 5 hour exposure.  The glucose profiles are predictable with mostly carb raising levels.  Lactate is increased by carb and alcohol to statistically similar degree.  Since these were mixed meals, albeit enriched in one macro or another, the insulin responses were not as pronounced as one might presume.  I think most often misunderstood or not well characterized is the glucagon response.  Glucagon is actually suppressed by the high carb meal, but it is increased considerably by protein, fat and alcohol.  A common "out" given to protein for it's insulinogenic properties is the fact that it stimulates glucagon while carbs do not.  Clearly it does, but so, too, do fat and alcohol. 

Next up we have the energy expenditure and oxidation rates of glucose and fatty acids.  Note that DIT = Dietary Induced Thermogenesis.  As reported in Nutrient Fates, alcohol is highly thermogenic!  In this study exceeding protein.  However at the same time, alcohol suppresses fatty acid oxidation moreso than even carb.  The DIT for carb and fats were essentially the same, which differs slightly from Jequier's factors as in Nutrient Fates.  This illustrates that except at extremes, manipulation of carb:fat ratios are unlikely to alter total energy expenditure.  I note that fat oxidation rates are suppressed (albeit to a negligible degree for protein and fat) following all meals!  So much for eating fat stimulating fat burning...  Comparing the carb and alcohol meals we see that DIT for carb is less than that for alcohol, and yet the alcohol consumers virtually shut down fat oxidation (as would be expected because of obligate hepatic alcohol metabolism).  So ... does fatty acid oxidation rate necessarily correlate with energy expenditure?  It would appear not.   Meanwhile, only carbohydrate stimulated its own oxidation considerably, and since all meals contained some carbs, we see that carb oxidation is increased after all meals.  

And what of the mastermind hormone leptin?   I don't see any "spiking" going on ... unless you consider the alcohol-induced anti-spike!  Maybe there's something to this Spiked Leptinade after all ;-) ... or perhaps the "hard stuff" is the anti-Leptinade!

Clearly leptin is not a postprandially stimulated hormone in this study.  Yeah, carbs seem to suppress it the least in the postprandial period, but mostly it's carbs for which the leptin-to-FAoxidation correlation falls apart.  

Lastly, let's look at postprandial lipids.  Despite the alcohol meal containing ~38% of the fat of the fat meal, the postprandial AUC for circulating triglycerides is almost equal to that of the high fat meal and vastly exceeds both the carb and protein meals containing roughly equal and slightly more fat respectively.   Moral?  Don't drink and eat fat!  How about that all important availability of NEFA?  You know, the stuff your insulin is starving your mitochondria of causing your metabolism to be so effed up?  Well, we note that all meals ultimately lower NEFA levels.  Somewhat surprisingly (though apparently not significantly) protein seems to lock away your fat the most (and we know how fattening protein is!).  Sure carbs play the role of metabolic bully (bad, bad carbs!!) and, as might be expected so does alcohol.  But it is worth noting that even the fat meal reduces NEFA somewhat.  But fear not peeps, as you can see, the fats are released by hour 5.  And cheers!!  If you've had alcohol, you're on the way to fat burning in hour 6!!  I note that I've omitted the incretin data (GLP-1, GLP-2, GIP) , please feel free to check it out!

Yes, I realize there's not much original or groundbreaking in this post.  But I thought it might be helpful to share it and put the graphics out there.  As a Ricky Martin fan once said "pictures are worth more than a thousand words".  The next time you read claims about what this or that macro does to this or that hormone level or your metabolism, remember these images!