。
Dietary fiber is effective for losing weight.
Literal
Food-fiber [topic-は] diet [to-に] effective is-[copula-だ].
A simple health-claim sentence. 食物繊維 ('dietary fiber') is a kango compound standard in nutrition labels. 効果的 ('effective') is a na-adjective formed with the productive suffix ~的 — which turns kango nouns into na-adjectives. ダイエット is the katakana loanword, specifically meaning 'weight loss' in Japanese (not 'diet' in the broader sense of 'what one eats').