Some of the controversy is due to inferring causality from associative links between an illness and a factor of interest. Another factor is the dependence of journalists upon unbiased interpretation from experts, which is not always available.
Consequently the public believes it has no reliable source of advice on these topics. When a particular health topic is popular, public attitude and behaviour is swayed violently by each new possibly relevant study that is reported, reinforcing and debunking fads overnight.
2. A study on obesity was reported in the American press as showing that obesity did not hasten death as much as previous medical research had shown. Closer inspection of the study revealed that it left out of account the diseases that are thought to be aggravated by obesity.