Given how much press is devoted to articles on losing weight and "the obesity epidemic," you might think you — and the experts — are pretty knowledgeable. So, test yourself. Are the following statements true or false?

  • Snacking causes weight gain.
  • Eating breakfast regularly prevents weight gain.
  • Losing weight slowly is better than losing weight fast.

If you answered "true" to any of these, you may not know as much about dieting and obesity as you think you do. But you are in good company. Even health professionals have lost sight of some of the facts about obesity and weight loss and dispensed advice based on presumptions that have no scientific support.

The authors of the report, published last week in the New England Journal of Medicine, believe that these myths and presumptions are beliefs held by not only the general public, but also by many health professionals, academics, regulators, and journalists.

These are the findings of a study by a group of researchers led by David Allison, a biostatistician at the University of Alabama at Birmingham. They used Internet searches of popular media and scientific literature to find which popular beliefs about gaining and losing weight were supported by scientific evidence and which weren't.

Debunking the Myths

The researchers found seven myths in wide circulation and nine facts that may actually help people lose weight:

Myth #1 Small sustained changes in calorie intake or physical activity will produce large weight loss over time.
Truth: Body composition and metabolism change over time and alter our bodies' energy requirements, so ignore all advice like “cut 100 calories a day to lose 10 pounds in a year.” Science shows it doesn’t work like that.

Myth #2. Setting realistic goals for weight loss is better than setting more ambitious goals.
Truth: The science suggests that people generally will lose more weight if they set more ambitious goals for themselves.

Myth #3 Losing weight slowly is better than quickly; rapid weight losses are more likely to be regained.
Truth: Scientific evidence shows that those who drop more weight quickly are more likely to weigh less years later.

Myth #4 People who are ready to lose weight will be more likely to adhere to weight-loss treatment.
Truth: The science says that assessing the readiness for change of an individual neither predicts nor helps with weight-loss.

Myth #5 Physical education classes are important in the prevention and treatment of childhood obesity.
Truth: In their current form, PE classes are not long enough or intense enough to make a difference one way or another, and the level of physical activity that would be required to make a difference (from a scientific standpoint) probably isn’t realistic in the conventional school setting.

Myth #6 Breastfeeding protects infants against obesity.
Truth: Though breastfeeding offers many benefits to both mother and infant, there is no scientific data that show it protects against obesity in offspring.

Myth #7 Sex burns anywhere from 100 to 300 calories for each partner.
Truth: Calories burned during sex can be estimated by a scientific formula. Intercourse lasts on average about six minutes and burns just slightly more calories than sitting on the couch for six minutes.

Facts You Can Count On

Just as important as debunking the myths about weight-loss is being able to recognize widely accepted weight-loss advice that has never been proved or disproved. Some examples:

1) Eating breakfast regularly protects against obesity;

2) Eating and exercise habits formed in early childhood influence weight throughout life;

3) Eating more fruits and vegetables will result in weight-loss or less weight gain regardless of any other changes one makes;

4) Yo-yo dieting is linked to increased mortality;

5) Snacking contributes to weight gain; and

6) The availability of amenities like sidewalks and parks in a community reduces obesity.

Though there is some basis for assumption for each of these, at present there is no science to back up any of them.

The authors of the report believe that these myths and presumptions are beliefs held by not only the general public, but also by many health professionals, academics, regulators, and journalists. They argue that promoting "unsupported beliefs may yield poorly informed policy decisions, inaccurate clinical and public health recommendations, and an unproductive allocation of research resources and may divert attention away from useful, evidence-based information.”

Exercise is beneficial even if it doesn’t result in weight-loss because it can lessen the ill effects of obesity.

The study lists nine "Facts about Obesity" that are supported by scientific studies. Some are fine points that are often lost in favor of broader, more sweeping (and less true) statements:

  • Genes are not destiny. Environmental changes can promote as much weight-loss as the best pharmaceutical products.
  • Diets (eating fewer calories) work, but diet strategies (eating more vegetables, for example) or recommending a diet to someone doesn’t work.
  • Exercise is beneficial even if it doesn’t result in weight-loss because it can lessen the ill effects of obesity.
  • A good dose of substantial exercise helps with long-term weight maintenance.
  • Obesity requires ongoing management.
  • Programs for overweight children that involve the parents and the home work the best.
  • Programs that provide pre-packaged meals and meal-replacement products work because they offer structure and control.
  • Some weight-loss drugs are moderately effective in treating obesity.
  • In certain individuals, bariatric surgery works and can be lifesaving.

So while weight-loss advice is dispensed everywhere from doctor’s offices to magazine stands, much of what we’ve been led to believe may not have any basis in science. While we’re working on finding solutions to the problem of obesity, we need to be sure that what is recommended has been evaluated for accuracy and efficacy. This report was published in the New England Journal of Medicine.