As our waistlines have grown, so have the conventional wisdoms attached to obesity.

If we just exercised every day for 20 minutes, we would lose weight. Weight loss is just a matter of willpower. Going back to eating like the olden days will make us lose weight.

But scientists don't often agree with these views, according to a Frontline report by the New York Times .

In fact, scientists say many of the so-called facts about obesity amount to speculation or oversimplification of the medical evidence. For example, diet and exercise do matter, but these environmental influences alone do not determine an individual’s weight. Body composition also is dictated by DNA and monitored by the brain.

And we never ate as well as we thought, even back in the old days.

Check out the full article and see what myths you've fallen prey to.

-- Amanda Barrett, amNY.com