I'd say you're misinterpreting what belief implies here
Tradition isn't proof, but also it doesn't harm credibility, at least to coherent people, and that's how it should be*
Eventually if there's enough proof, the consensus shifts, regardless of how much initially people try to deny it
Fasting goes against recent consensus, yet it's becoming both more researched and more recommended (At the very least at the layman level, I'm no dietician)
* Something working doesn't tell you why it works, so it's important to be rigorous and always check, else you risk cargo-culting unnecesary or even risky things
Eventually if there's enough proof, the consensus shifts, regardless of how much initially people try to deny it
Fasting goes against recent consensus, yet it's becoming both more researched and more recommended (At the very least at the layman level, I'm no dietician)
* Something working doesn't tell you why it works, so it's important to be rigorous and always check, else you risk cargo-culting unnecesary or even risky things