Quote from Gabfly1:
I was listening to a science show on the radio yesterday, and a 19-year study conducted in Japan was briefly discussed. The study followed the lives of a very large group of people during that period, starting at ages between mid-40s and mid-50s. The findings showed that those people who ate meat sparingly, one meal every second day, had more autonomy in later life than other groups in the study. Other groups included those who consumed meat daily as well as those who ate no meat at all. Bottom line, some meat helps to maintain muscle mass needed for general autonomy in older age since muscles naturally atrophy with age. This study did not deal with ideals, but rather simply followed a large sample of people who lived their lives as they usually do.
Interpretation of the results may vary, but those were the general conclusions drawn by the people who conducted the study.