This is from http://aginginaction.com/2014/03/age-determines-optimal-protein-consumption/ Read the whole article there. Here are the highlights
Researchers recently discovered that the health impacts of eating protein change as we age. Their study looked at the impact of protein consumption on overall mortality, cancer, and diabetes risk in a nationally representative epidemiological study of 6,381 individuals age 50 and better in the United States.
For individuals over 66, the researchers found the opposite outcomes for the relationship between overall mortality and cancer mortality and protein consumption. For this age group, the high-protein consumption group showed a 23 percent reduction in overall mortality, and the moderate-consumption group showed a 21 percent reduction in overall mortality than the low-protein group. This was not affected by the percentage of calories from fat, carbohydrates, or animal proteins. The older group also showed a 60 percent reduction of cancer mortality in the high-protein group compared to the low-protein group.
To look at why different levels of protein consumption are optimal at different ages, the researchers used blood tests and animal models. For middle-aged adults, it appears that high protein consumption leads to an increase in the molecule IGF-1. Higher levels of this molecule in the blood are associated with an increased risk of cancer death. Why this pattern was not observed in older adults is not clear.