Womens health initiative
The Womens health initiative (WHI) is a large, federally funded study of several interventions designed to make people healthier. Unfortunateley according to several recent publications they don't seem to work
Three articles in last week's JAMA showed that a low-fat diet didn't protect against either cancer or heart disease. Then in this weeks NEJM, we find out that calcium supplementation did little if anything to increase bone density or prevent fractures and nothing to prevent colon cancer.
Why? Well one problem is that it is hard to get people to change their lifestyle much. The women assigned to a low-fat diet still ate 25% fat 1 year in and 28% after 5 years, dowm for 37% at baseline. In the calcium supplementation study there was actually substantial improvement in patients who actually tood the supplements. But the 40+% of women who were assigned to take them and didn't (defined as <80% of pills taken) are included in the primary statistical analysis, diluting out the effect.
Most trials are analyzed based on what is called "intention to treat" meaning that everyone randomized to a group (calcium supplementation or placebo in this case) is included, whether they took the treatment or not. The reason is clear if you think of say a trial of a new medicine for cancer. If you exlude patients who didn't finish treatment (say because they died) you might make the treatment look better (by kicking out sicker patients). So you analyze the data looking at everyone randomized to get treatment.
In lifestyle interventions, this reasoning is not so clear. What we really want to know is whether making change X will decrease the risk of disease Y. We already know it is hard to get patients to substantially modify their behavior, that is why so many people still smoke. But that doesn't mean that paitents who do change won't benefit.
In summary, both a healthy diet and calcium supplementation may be good ideas, at least from the view of the individual. From a public health perspective, it is hard to know if patients will follow the advice enough to make a difference. As William James said it is easy to have beliefs, the hard part is getting our beliefs into our muscles.