I usually recommend a slightly reduced protein intake (1-1.2g/kg body mass/day (see feature article in 220 Triathlon magazine out May 10, 2005) during rest days. This is because protein intake is supplemented by Low Biological Proteins from carbohydrate food sources. This can add another 30% to your overall protein intake. Your recovery is optimised within the 1st 2 hours post exercise at a 7-8% conversion rate (carbohydrate to glycogen storage in skeletal muscles and liver) per hour and subsequently declines to 5% per hour. Recovery can take up to 24 hrs post exercise so utilising the 1st 2 hours post exercise is vital. Your recovery days therefore dont require extra protein by way of protein shakes.