10 Causes of Weight Gain That Doctors Have Changed Their Minds About

Spanish TV personality Maria Jose Suarez poses with a line of Zone Diet products. Is any one diet better than the rest? Pablo Blazquez Dominguez/WireImage/Getty Images

Back in 1905, future U.S. President William Howard Taft worried about so much about his girth − he weighed in excess of 300 pounds (136 kilograms) − that he began corresponding with Dr. Nathaniel E. Yorke-Davies, an English weight-loss guru. Yorke-Davies put Taft on a strict low-carb, low-fat regimen that included a three-page list of foods he was permitted to eat and ones he had to avoid. It actually worked − Taft lost 60 pounds (27 kilograms). Feeling successful, Taft then strayed from the diet and got even heavier than he was before [source: Klein].

Sounds familiar, doesn't it? Since Taft's time, Americans have followed other diet doctors, and tried various sorts of exotic regimens − ranging from the 1930s Hollywood Diet, which emphasized eating a grapefruit with each meal to today's Paleo Diet, which supposedly aims to emulate our hunter-gatherer ancestors [sources: Rotchford, Jabr].

We've heard plenty of weight-loss advice over the years as well, about which foods to eat, when to eat them and which combinations to avoid. And we've seen weight-loss experts give conflicting opinions or change their minds about what's really making us fat.

In truth, a lot of popular ideas about weight loss and gain, including ones that once were championed by medical experts, haven't held up to scientific scrutiny. Here are 10 truisms that are now being questioned.