Feb. 1, 2012 -- 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.
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.