Health related research in a nutshell.

[Mosby]

6. I think a lot of health advise changed because of new info, like with cholesterol.

But sadly too much of it is due to shitty research. Like with that now infamous Harvard epidemiological study in 2001 that claimed moderate drinkers had lower heart disease, higher HDL levels and lived longer:

"There's good evidence that, in general, moderate drinkers who average one to two drinks a day tend to live longer," says Eric Rimm, professor of epidemiology and nutrition and director of the Program in Cardiovascular Epidemiology at the Harvard T.H. Chan School of Public Health. "Whether that is directly linked with alcohol, other lifestyle factors, or some combination is still being explored."

The public and media believed this, even though it was poor research using faulty data and weak experimental design. New studies, including meta analysis have shown that light drinkers do not live longer.

One reason for this is plain old sample error. Light drinkers are a different demo than non-drinkers, who are considerably less affluent than light drinkers, and maintain different diets, level of exercise etc. This can be controlled to an extent with good design, but not always.