"Vad tycker du om man säger att socker är farlig för hälsa?" One can understand this, but "vad tycker du om PÅSTÅENDET att - socker är farlig för hälsa" is much better grammaticly. Because if you leave it as it is in Swedish it is as if you are wondering "is it okey that one SAYS it", the emphasys is on word "say" as the sentece is build right now. Also "hälsaN". you need "N", because "om man säger" is refering to a claim, than you need the article form "N".