。
Daily exercise is effective for preventing obesity.
Literal
Every-day [possessive-の] exercise [topic-は] obesity [object-を] prevent [purpose-のに] effective [copula-である].
~のに有効 ('effective for doing X') uses the nominalizer の + に to create a purpose phrase — distinct from the concessive のに ('despite'). である is the formal written copula. 肥満 ('obesity') and 有効 ('effective') are formal written vocabulary.