Logical Reads x Buffer Pool Content

Hi All.I'm troubleshooting a specific query performance, and one of the first thing that i do is to check the statistics IO output.Below is one of the lines from statistics io result Table 'XXXXXX'. Scan count 0, logical reads 571960, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.But when i look into the buffer pool content (using sys.dm_os_buffer_descriptors), the total pages is 7.941 for the same table.if i run the same query again, the result is the same (statistics io reports a lot of logical reads , but the buffer descriptors contains far less pages).Does anyone know why these values are so different?I'm using sql server 2014 SP2 enterprise edition.Thanks,Luiz