So that's why it's so hard to know whom to believe.

The New York Times this week offers a fascinating question: Is it possible doctors have succumbed to an irresistible pressure to agree that fat is bad for us when there's no such proof?

In Diet and Fat: A Severe Case of Mistaken Consensus, (Findings, October 9th) columnist and debunker John Tierney talks about why physicians such as former Surgeon General C. Everett Koop might have made dietary recommendations based on received wisdom rather than on actual evidence. Tierney presents evidence of a phenomenon social scientists call 'informational cascade' in which one person tends to agree with the opinions of trusted others rather than evaluating the evidence independently. As agreement on the issue builds, dissenters are ostracized until eventually an entire community of so-called experts may very well believe something that simply hasn't been proved.