Full Idea
Nietzsche believed that by elevating the importance of the mind, Plato downplayed the wonders of the body, and by searching for a timeless Truth he degraded the indisputable fact of human temporality.
Gist of Idea
Nietzsche felt that Plato's views downgraded the human body and its brevity of life
Source
report of Friedrich Nietzsche (Beyond Good and Evil [1886], Pref) by David Roochnik - The Tragedy of Reason Prol. X
Book Reference
Roochnik,David: 'The Tragedy of Reason: the Platonic logos' [Routledge 1990], p.-7
A Reaction
Both ideas are very important. The second is widely misunderstood. Nietzsche was not a denier of truth. He asked us to scrutinise the role and value we assign to truth.