Medical News by Miriam E. Tucker

We know we don't have a "magic bullet" yet when it comes to weight loss, but at least we can count on some old standbys -- like eating a little less each day adds up over time, breastfeeding means lean children, and when all else fails, sex can burn the cheesecake off. Right?

Not so fast.

An article published online in the New England Journal of Medicine shows that some of the most firmly held beliefs about weight loss are unproven or downright untrue, based on analysis comparing what we hear in the popular media to what we actually know from reliable research.

“From social media outlets like Facebook, to mainstream television news, to dietetic and nutrition textbooks, these myths are perpetuated, irrespective of the scientific evidence,” says researcher Krista Casazza, PhD, RD, from the department of nutrition sciences at the University of Alabama at Birmingham, in a prepared statement.

The researchers discuss a total of seven myths and back it up with evidence. The myths are:

Small changes in how much you eat and/or exercise will result in large, long-term weight changes.

This was based on the old idea that 3,500 calories equals 1 pound of weight. But it does not take into account the fact that energy requirements change as body mass changes over time. So, as weight is lost, it takes increasingly more exercise and fewer calories to keep the weight off.

Realistic weight-loss goals will keep people motivated.

This idea seems reasonable, but it is not supported by evidence. In fact, several studies have shown that people with very ambitious goals lose more weight (i.e. TV's The Biggest Loser).

Slow, gradual weight loss is best for long-term success.

Actually, a large review of gold standard trials found that rapid weight loss via very-low-calorie diets resulted in significantly more weight loss at six months, and the differences in weight loss persisted up to 18 months.

People who feel "ready" to lose weight are more likely to succeed at it.

It does sound like a logical idea. But evidence suggests that first defining "readiness" doesn't predict weight loss or help to make it more likely to happen.

Current-day gym classes play a key role in reducing or preventing childhood obesity.

Physical education, as typically provided, has not been shown to reduce or prevent obesity.

Breastfeeding protects the child from obesity.

While breastfeeding can provide health benefits for the child, the evidence does not support the idea that preventing obesity is one of them.

A bout of sexual activity burns 100 to 300 calories per person.

With intense sexual activity, a 154-pound man burns approximately 3.5 calories per minute. However, given that the average amount of time spent during sex is about six minutes, this man might expend about 21 calories total. But, he would burn about 7 calories per minute just lying on the couch, so that amount has to be subtracted, which gives a grand total of 14 calories of energy expended.

The article also explores six "presumptions," or widely accepted beliefs that are neither proven nor disproven. They are:

Eating breakfast prevents obesity.

Actually, two studies showed no effect of eating vs. skipping breakfast.

Childhood is the time to learn to exercise and eat well.

While it certainly can't hurt, there's no rigorous evidence to support it.

Adding fruits and vegetables to the diet results in weight loss.

Adding more calories of any type without making any other changes is likely to cause weight gain. Eating fruits and vegetables is healthful, however.

Yo-yo dieting increases your risk of death.

While some studies have shown a debatable link, none have actually proven a cause and effect.

Snacking contributes to weight gain and obesity.

There's no solid evidence to support this belief.

More parks and sidewalks means less obesity.

Again, the evidence just isn't there.

9 Facts

Finally, the authors offer nine facts about obesity and weight loss that are supported by evidence.

"The myths and presumptions about obesity that we have discussed are just a sampling of the numerous unsupported beliefs held by many people, including academics, regulators, and journalists, as well as the general public. Yet there are facts about obesity of which we may be reasonably certain -- facts that are useful today," Casazza says.

Here they are:

• Your genes are not your destiny. Moderate environmental changes can promote as much weight loss as even the best weight-loss drugs.
• Diets do produce weight loss, but attempting to diet and telling someone to diet are not necessarily the same thing.
• Even without weight loss, physical activity improves health.
• Physical activity or exercise in the right amounts does help people lose weight.
• Continuation of conditions that promote weight loss helps people keep the weight off. Think of obesity as a chronic condition.
• For overweight children, involving the family and home environment in weight-loss efforts is ideal.
• Providing actual meals or meal replacements works better for weight loss than does general advice about food choices.
• Weight-loss drugs can help some people lose weight.
• Bariatric surgery can help achieve long-term weight loss in some people.

Several of the researchers -- not including Casazza -- disclosed a long list of financial relationships with a wide range of groups, from Coca-Cola to Kraft Foods, to pharmaceutical companies such as Vivus and Arena -- companies that make two weight-loss drugs recently approved by the FDA. The study was supported in part by the National Institutes of Health.

Regardless, the researchers write that what they included in their article "are just a sampling of the numerous unsupported beliefs" out there. It is important, they say, to banish myths with "scientific method and logical thinking."

“As scientists, we have the responsibility to present the evidence as it exists without inflating ideas and contributing to popular misconceptions. As a registered dietitian, I feel that providing evidence-based statements about weight loss is essential,” Casazza says.