Protein absorbtion (or any nutrient for that matter) would depend on 2 things - clean stomach lining and intestines and quality unadulterated whey protein powder consumed. I take about 40g per serving with filtered water on an empty stomach except right after workouts (I up the protein to 60g then). I also take small fiber tablets twice daily (early afternoon and just before bed) along with my other supplements.
The key is the amount of clean lining in your system to absorb theprotein. It will not matter if your taking in only 15g protein if you're not doing everything you can to help the body digest it properly. If your interested in more on this, research Jay Cutler's dietary habits. You'll be amazed at just how hard he works on keeping his internals in top order.
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