Washington (AFP) - A few years ago, two researchers took the 50 most-used ingredients in a cook book and studied how many had been linked with a cancer risk or benefit, based on a variety of studies published in scientific journals. The result? Forty out of 50, including salt, flour, parsley and sugar. "Is everything we eat associated with cancer?" the researchers wondered in a 2013 article based on their findings. Their investigation touched on a known but persistent problem in the research world: too few studies have large enough samples to support generalized conclusions. But pressure on researchers, competition...