Medical/Scientific Conventional Wisdom That Turned Out to be Wrong:

For a paper I'm working on, I'm collecting recent examples of conventional wisdom among health professionals that turned out to be wrong once the issue was studied in more depth. I'm not looking for eccentricities, but for generally accepted theories that had a reasonable basis, but have since been refuted or at least strongly challenged. Recent examples I can think of: (1) that it's generally good to give estrogen to post-menopausal women; (2) that being overweight, but not obese, lowers one's life expectancy; (3) that eating lots of fiber reduces the risk of colon cancer; (4) that eating tomatoes lowers the risk of prostate cancer. More examples, along with citations to any relevant scientific studies (including for the examples above), would be most appreciated. Wisdom from commentors regarding how unproven theories become conventional wisdom in the absence of hard data would also be welcome.