7 common beliefs about obesity and weight loss that are total myths

More than a third of US adults are obese. But despite its increasing prevalence in America and around the world, obesity — and what actually causes weight gain and loss — is frequently misunderstood.

Frustrated by rampant misinformation, a large group of doctors and scientists teamed up to set the record straight in a recent article in The New England Journal of Medicine.

The misinformation "persists ... despite contradicting evidence," the researchers wrote.

Here are seven of the most common myths they identified.

Myth #1: Weight loss from a particular diet and exercise program is predictable and consistent.

There's a popular idea that cutting or burning 3,500 calories over time will lead to one pound of weight lost, while adding that many calories will lead to a pound gained.

In reality, one study found that people only lost about 20% as much as would be expected if that idea were true: just 10 pounds (not 50) after walking a mile every day for five years.

And over the long-term, it's much more complex. It turns out that results can vary significantly among individuals, and that as the body changes, the balance of food and exercise it needs to drop pounds changes as well. Researchers are now moving toward the idea that every person's diet needs to be carefully personalized.

As for the original idea? That's based on short-term studies, primarily in men, the researchers write — so it's erroneous to apply to everyone.

Myth #2: Without realistic weight loss goals, people will get frustrated and shed fewer pounds.

While the researchers call this"a reasonable hypothesis," it turns out there's no real evidence to back it up.

Some studies have changed participants' goals to be more realistic and found that it had no effect on outcomes. In fact, "more ambitious goals"— rather than more realistic goals — "are sometimes associated with better weight-loss outcomes," the researchers write.

Myth #3: "Slow, gradual weight loss" is better in the long-term than "large, rapid weight-loss."

Actually, people in studies who showed "more rapid and greater initial weight loss" also have "lower body weight at the end of long-term follow-up," the researchers write.

As far back as 2001, researchers suggested that greater weight loss during the beginning of a weight-loss program was tied to longer-term success at keeping the pounds off. A 2010 review of research backed this up, adding that people with rapid weight loss early on were not more likely to gain back the pounds than people who lost weight gradually.

Still, no one should embark on a serious weight-loss program without talking to a doctor about their goals and strategies. A doctor can advise how much weight loss would be too rapid for a particular individual. There can be health consequences if weight loss is too aggressive, and many rapid-weight-loss programs involve questionable strategies that are actually unhealthier and more dangerous than the extra weight itself.