Monday, February 11, 2013

Seven Myths About Obesity And Weight Loss?

Whether we cruise the internet, turn on the TV or simply open up our email Inbox, we are bound to encounter advice regarding obesity and weight loss. The problem is that a lot of the circulated opinions about obesity and weight gain are only poorly supported by medical and scientific evidence. The recent paper “Myths, Presumptions, and Facts about Obesity” published in the New England Journal of Medicine on January 31, 2013 by Krista Casazza and colleagues investigates popular notions about obesity and tests whether they are actually backed up by peer-reviewed, evidence-based studies. Their findings are quite surprising and unravel many of the “myths” that relate to obesity and weight problems. The authors refer to these notions as “myths”, because they were unable to find adequate evidence to back them up and even find some evidence that actually refutes the notions. Unfortunately, the data presented by the authors does not always provide definitive evidence, so it may be rather premature to dismiss these widely held beliefs as “myths”.

Here are the seven “myths” about obesity and weight gain that the authors discuss:

Myth number 1: Small sustained changes in energy intake or expenditure will produce large, long-term weight changes.

The authors claim that this is a myth, because it is based on the assumption that small dietary or activity changes yield benefits that continue to accumulate and result in large changes. They think that these calculations overestimate the achieved weight loss, because they do not adequately take into account that the metabolism adapts to the ongoing weight loss. A very obese person with a high caloric intake may respond strongly to a minor increase in daily exercise levels, but the degree of weight loss will decrease over time.
I have to disagree with Casazza and colleagues on this point, because I think that their analysis does not refute the idea of small sustained changes having long-term benefits. One can disagree about the magnitude of the long-term benefit, but there is still a long-term benefit.

Myth number 2: Setting realistic goals for weight loss is important, because otherwise patients will become frustrated and lose less weight.

Casazza and colleagues cite multiple studies which show that ambitious weight loss goals may be associated with better outcomes.

Myth number 3: Large, rapid weight loss is associated with poorer long-term weight-loss outcomes, as compared with slow, gradual weight loss.

The authors point to a meta-analysis (summary analysis of multiple published studies) which showed that very low energy diets (rapid weight loss) and low energy diets are similarly successful in terms of achieving weight loss.

Myth number 4: It is important to assess the stage of change or diet readiness in order to help patients who request weight-loss treatment.

The evidence does not support the need to wait for people being “ready” for weight loss. It may be best to start right away.

Myth number 5: Physical-education classes, in their current form, play an important role in reducing or preventing childhood obesity.

The authors of the paper summarize the results of multiple studies which did not show any statistically significant and consistent benefit of increasing physical education time in school on childhood obesity. They state that there is probably a level of activity that will be beneficial, but that this level may not be achieved in the limited amount of time that children have in school for physical education.
The problem with the analysis of the Casazza and colleagues is that they dismiss the findings as “inconsistent”, but this inconsistency may reflect that some children do benefit from the intervention while others do not. One study, for example, showed a benefit in girls that were overweight, but not in boys. This “inconsistency” does not necessarily invalidate the notion, it merely means that we need to identify the group of children that are most likely to benefit and to perhaps modify the type and duration of physical education in schools to help even more groups of children.

Myth number 6: Breast-feeding is protective against obesity.

Casazza and colleagues reviewed all the major studies in this area and found no significant evidence that breast-feeding children protects them against obesity, but they concede that breast-feeding may be associated with other benefits for the child, unrelated to obesity.

Myth number 7: A bout of sexual activity burns 100 to 300 kcal for each participant.

The authors calculate the amount of calories burned during sexual activity and estimate that the actual amount is probably closer to 20 to 30 kcal (calories) and not 100 to 300

These are the seven “myths” that the authors claim to have debunked. I also think that it is important to note the disclosures at the end of the article, which shows that the authors have very strong ties to food manufacturers. Here are the financial disclosures for just one of the authors:

“Dr. Astrup reports receiving payment for board membership from the Global Dairy Platform, Kraft Foods, Knowledge Institute for Beer, McDonald’s Global Advisory Council, Arena Pharmaceuticals, Basic Research, Novo Nordisk, Pathway Genomics, Jenny Craig, and Vivus; receiving lecture fees from the Global Dairy Platform, Novo Nordisk, Danish Brewers Association, GlaxoSmithKline, Danish Dairy Association, International Dairy Foundation, European Dairy Foundation, and AstraZeneca; owning stock in Mobile Fitness”

These financial ties do not invalidate the analysis, but they should be considered when interpreting the results.

Overall, I think this is an important paper, because it shows us that we often operate under certain assumptions about obesity and weight loss without there being adequate evidence to back it up. This highlights the need for more unbiased research in this area. However, I am disappointed by some of the analyses made by the authors, when they summarily dismiss a belief as a “myth”, just because there are some inconsistencies or differences in estimated benefits. Instead of using the somewhat sensationalist term “myth”, it would have been better if the authors had just focused on pointing out weaknesses in the current evidence and need for more studies.

Image credit: Painting “Schlaraffenland” (“The Land of Cockaigne”, 1567) by Pieter Bruegel the Elder – via Wikimedia Casazza K, Fontaine KR, Astrup A, Birch LL, Brown AW, Bohan Brown MM, Durant N, Dutton G, Foster EM, Heymsfield SB, McIver K, Mehta T, Menachemi N, Newby PK, Pate R, Rolls BJ, Sen B, Smith DL Jr, Thomas DM, & Allison DB (2013). Myths, presumptions, and facts about obesity. The New England journal of medicine, 368 (5), 446-54 PMID: 23363498


  1. In 2009, I lost 60 pounds in six months, and I thought I was a badass, because I'd seen people go on Oprah and similar shows to brag about how they lost less weight than that in twice the time frame. But after a while I got lazy and stupid, and I started eating the way Americans normally eat, and I soon re-acquired the weight problems that Americans normally have. So eventually I got a hold of my senses, and in the past two months, I've lost 32.5 pounds, which is a very swift rate of weight loss. In fact, most of the weight loss comes from one week in February, when I lost 20 pounds, and the past two days, in which I've lost 9 pounds.