Any one that has hung out in the gym for more than 5 minutes has probably heard that you can only absorb about 25 grams of protein in one meal. So is it true? I learned this in college, and have taken it as fact (with the likelihood of a standard deviation, of course). Recently I decided to read the original research to see exactly what that standard deviation might be. To my surprise (though it shouldn’t have been), I discovered that there was no original research. I went as far back as the database allowed (the 70’s), and there was nothing.
Most of what is available, is comparing various proteins and amino acids and their effects. The short version of all of that research is that typically, long acting and slow digesting proteins, such as animal meat and casein from dairy, work better for overall nitrogen balance and muscle growth than short acting proteins like whey. The exception for this is in the elderly. That is mostly likely attributable to poor gut health. Some research does suggest that the fast proteins, like whey, work better post workout for increased muscle and strength, and there is some evidence for this. But still, overall, the slower digesting proteins have more impact. Why? Because, as with all recovery, most of it happens while you sleep. The 30 gram post workout whey protein shake that you had only sustained blood protein levels for about 2 hours. Your average protein source (i.e. chicken, fish, beef, etc…) will sustain blood protein levels for up to 8 hours. This is because they release into your blood slower (this is because the take more work to breakdown).
That brings me to the next point. Research does show that more complex meals, and larger meals can take upwards of 3 hours (normal) to fully digest and absorb. So your body will actually adjust digestion rate as needed to fully extract nutrients. Any extra amino acids then floating around in your system after absorption will be turned in to urea and excreted. This is more likely with a fast absorbing protein, like whey, as it causes a surge of amino acids into the blood. So again, a slow acting or slow digesting protein is better.
So there is some validity to this myth, because eating protein throughout the day will yield better blood protein levels throughout the day and hence better results. But, from an absorption stand point, this is absolutely a myth. If you have a healthy gut, and eat 80 grams of protein in one sitting, there is nothing scientific to suggest that you will not digest and absorb all 80 grams.