Many of the beliefs we have about obesity are myths or presumptions that have no good scientific evidence to back them up, according to a paper published Thursday in the New England Journal of Medicine (NEJM).
Written by 21 different obesity experts from a variety of institutions (and funded by a grant from the National Institutes of Health), the paper identifies what the authors call “false and scientifically unsupported beliefs about obesity” that “are pervasive in both scientific literature and the popular press.”
Unfortunately, however, nine of those 21 authors have financial ties to processed food manufacturers, pharmaceutical companies or weight-loss programs — major conflicts of interest that raise the question of possible bias in the paper’s findings.
The myths
With that rather large caveat in mind, here are the authors’ seven obesity-related myths, which they define as generally held beliefs that have been scientifically refuted:
- Eating just a little bit less or exercising just a little bit more will produce large weight changes over the long term.
- It’s important to set realistic weight-loss goals if you want to keep from getting frustrated and giving up on your weight-loss plan.
- Losing a lot of weight quickly is less effective over the long term than losing weight slowly.
- You have to be highly motivated to lose weight before you can be successful at it.
- School physical-education classes, as currently designed, play an important role in reducing or preventing children from becoming obese.
- A bout of sexual activity burns 100 to 300 calories. (“Given that the average bout of sexual activity lasts about 6 minutes,” write the study’s authors, “a man in his early-to-mid-30s might expend approximately 21 [calories] during sexual intercourse. Of course, he would have spent roughly one third that amount of energy just watching television.”)
The presumptions
And here are the author’s six obesity-related presumptions, which they define as generally held beliefs that have been neither proven nor disproven [with my bracketed comments]:
- Regularly eating (versus skipping) breakfast is protective against obesity.
- Early childhood is the period in which we learn exercise and eating habits that influence our weight throughout life. [Lifetime weight is more a function of genetics than of early learning, say the authors.]
- Eating more fruits and vegetables will result in weight loss or less weight gain, regardless of whether any other changes to one’s behavior or environment are made.
- Weight cycling (i.e., yo-yo dieting) is associated with increase mortality. [The studies that have found this association probably didn’t account for other confounding health factors, the authors say.]
- Snacking contributes to weight gain and obesity.
- The built environment, in terms of sidewalk and park availability, influences the incidence or prevalence of obesity. [Studies that have shown this association have been observational and thus can’t prove that “walkable” neighborhoods help reduce obesity, according to the authors.]
The problem of possible bias
Needless to say, given the authors’ financial connections with General Mills, Kraft Foods and other companies that sell snack foods, we’re left wondering just how unbiased they were to assert that, say, snacking doesn’t contribute to weight gain and obesity. Similar doubts surround the nine “facts” about obesity that the authors list toward the end of the paper, particularly these two:
- Provision of meals and use of meal-replacement products promote greater weight loss.
- Some pharmaceutical agents can help patients achieve clinically meaningful weight loss and maintain the reduction as long as the agents continue to be used.
Several of the authors have financial ties to pharmaceutical companies that make weight-loss drugs. And several others have close ties with Jenny Craig, a weight-loss company that sells prepared meals to its customers.
There are many myths about diet, food, nutrition and obesity — myths that are hindering people’s ability to maintain a healthy weight. Having experts address those myths in a major journal is a great idea. But, unfortunately, the financial conflicts-of-interest of this paper’s authors make it difficult for consumers to trust that the paper is truly sorting fact from fiction.