Eating about every 3 hours seems to be fairly optimal. To sum up some of Dave Barr's research (presented at the Test-Fest):
When you ingest protein, your body has a spike in protein synthesis (in layman's terms: eating protein = muscle growth). The spike lasts about three hours before you hit baseline again. However, ingesting additional protein during the synthesis period will not prolong the spike. So eating every 1.5 hours will not have any benefit.
Besides, do you really want to have to eat every ninety minutes?
So, (Candy) Barr, when is the Anabolic Index coming out?