I re-read the protein cycling article about two weeks ago and was interested-but as it was very old wasn't sure anyone would even remember it.
I have to be quite honest. I notice very little difference between 120 and 240 grams of protein a day and used both of these for months at a time, and I really think the body just starts making lots more enzymes (as TopSirloin pointed out the importance of enzymes) which break down protein quickly for use as fuel.
From an anabolism/catabolism point of view, there's only about 80 grams of protein in a pound of muscle, and you typically use up 80 grams of protein a day for daily needs. If your body was 100% efficient in delivering protein where you need it, you could gain 20 pounds in a year with 85 grams a day!
The whole theory of more protein is based on the body being very inefficient, but let's face it, if your eating 300 grams of protein a day, your body has become VERY inefficient at using protein. I TRULY believe that most Americans have an unknown gap in their nutrition somewhere that would be a weak link in building muscle before anyone would need 300 grams a day. We eat fruits and vegetables that grow to huge proportions fast and never absorb the micronutrients in the concentration that they were meant to.
I may try it some time, because, although I've built some muscle over the years, I gained as much or more, and as quickly when eating 90-120 grams a day as 200-240 grams a day.
If you read the article, you'll see that the key is to slowly lower your protein intake, and for a normal male, going down to 70-90 grams a day would be the least, and then to suddenly add back 100 to 150% more. Lets say you start at 200 grams/day. Week 1: 170, Week 2: 140, Week 3: 110, Week 4: 80.
Then say two weeks at 190-220 grams/day.
That's the theory anyway.