Last week the New England Journal of Medicine put out a special article on “Myths, Presumptions, and Facts about Obesity” (1). It received quite a bit of media coverage, including CBC News, so we thought we should take a look at the details.
They use the scientific research to disprove seven myths about obesity that they claim are common in both the scientific literature and popular press.
Myth # 1. “Small sustained changes in energy intake or expenditure will produce large, long-term weight changes (1).”
This myth is based on the commonly used math that one pound of fat contains 3 500 Calories. Theoretically, by expending an extra 100 Calories per day you should lose 50 pounds over 5 years; however, the actual amount is closer to 10 pounds (1,2). Clearly the reality doesn’t match the prediction. There are a lot of reasons for this including individual variability and the fact that as your weight decreases your energy expenditure also decreases.
A difference of 40 pounds is huge, BUT we also want to point out that 10 pounds of weight loss is excellent. The norm would be a gradual weight creep over this time!. We agree, you might not lose as much as expected BUT we don’t think this should discourage anyone from burning an extra 100 Calories per day, as there are still many benefits.
Myth #2. “Setting realistic goals in obesity treatment is important because otherwise patients will become frustrated and lose less weight (1).”
The authors reference the study by Linde et al. (3) that found that ambitious goals did not cause more participants to drop out of the program and sometimes were better – at least for women. It also turns out that when people are taught to set more realistic goals their expectations became more realistic but they don’t actually lose more weight (1). The message? Go ahead and dream big OR be realistic… the end result is likely to be the same.
Myth #3. “Large, rapid weight loss is associated with poorer long-term weight outcomes than is slow, gradual weight loss (1).”
To bust this myth the authors use a study that found that those who were “FAST” weight losers (0.68 kg/wk) lost significantly more weight than those in the “SLOW” weight losers group (<0.23 kg/wk) after 6 months. No surprise there BUT after 18 months the “FAST” group was still better off. There was also no difference in weight regain. The ultimate conclusion, fast weight losers lost more weight and did not seem to be more susceptible to weight regain than those who lost weight slowly (4).
Importantly, even the “FAST” group wasn’t experiencing drastic weight loss in this case. Looking at more extreme measures, Casazza et al. (1) also cite a meta-analysis that found greater initial weight loss with a very-low-energy-diet (<800 Calories per day) as compared to a low-energy-diet (800-1200 Calories per day). However, after one year there was no difference (Unfortunately, the reference they cite is not a meta-analysis so we don’t know where they got the information?). Honestly, if there is no difference, why subject yourself to less than 800 Calories per day? We say unless the drastic diet was ordered and supervised by a health professional, stick to more moderate methods. You’ll be much happier and end up in the same place……..possibly with a few more friends!
Myth #4. “It is important to assess the stage of change or diet readiness in order to help patients who request weight-loss treatment (1).”
It appears being more or less ready to make changes doesn’t make much of a difference. If you are ready enough to voluntarily choose to enter a weight-loss program, being “more ready” isn’t going to help (1,5).
Myth # 5. “Physical-education classes, in their current form, play an important role in reducing or preventing childhood obesity (1).”
Time spent in physical education classes does not seem to have consistent improvement on body-mass index in children (6). What you should read here is NOT physical activity isn’t beneficial in weight control BUT rather our physical education classes are not being taught in an effective manner! They need to be structured so that all children exercise vigorously for long enough; not sit around and learn the rules of basketball or watch the five athletic kids in the class play dodge ball. Another key point noted in the review AND not in this article is the conclusion that:
“Given that there are no harmful effects and that there is some evidence of positive effects on lifestyle behaviours and physical health status measures, ongoing physical activity promotion in schools is recommended at this time. ” (6)
Myth # 6. “Breastfeeding is protective against obesity (1).”
The authors note that a large randomized, controlled trial found no evidence that breastfeeding impacted obesity (1,7). Whatever! Really, there are so many other benefits to breastfeeding – bonding with your infant, lower cost, lower environmental impact, nutrient balance, immune health – it should be encouraged regardless of its role in obesity prevention.
Myth #7. “A bout of sexual activity burns 100 to 300 Calories for each participant (1).”
Again, we hope you have better reasons for having sex but if not… you’re about to be disappointed. Turns out the 100 to 300 Calories is an overestimation for most. Yes, you can burn ~210 Calories having sex; the problem is it takes an hour – the average is apparently about 6 minutes – in 1984, at least (8). As the authors (1) point out, that’s still more Calories than sitting in front of the TV and hopefully more enjoyable! Oh, where’s the romance? Good thing Valentine’s Day is just around the corner.
No Baloney’s thoughts. Yes, they disproved the myths but all of the myths were pretty harmless anyway. In no case was the behaviour encouraged by the myth increasing the risk of obesity or promoting bad habits. We say make the changes you can and need, keep having sex, breastfeed any infant that should arise, and send them to school and encourage better physical activity classes!
- Casazza K, et al. Myths, presumptions, and facts about obesity. N Engl J Med 2013; 368: 446-454.
- Thomas DM, et al. A simple model predicting individual weight change in humans. J Biol Dyn 2011; 5:579-99.
- Linde JA, et al. Weight loss goals and treatment outcomes among overweight men and women enrolled in a weight loss trial. Int J Obese (Lond) 2005; 29:1002-5.
- Nackers LM, et al. The association between rate of initial weight loss and long-term success in obesity treatment: does slow and steady win the race? Int J Behav Med 201; 17:161-7.
- Fontaine KR, et al. Dieting readiness test fails to predict enrollment in a weight loss program. J Am Diet Assoc 1999; 99:664.
- Dobbins M, et al. School-based physical activity programs for promoting physical activity and fitness in children and adolescents aged 6-18. Cochrane Database Syst Rev 2009; 1:CD007651.
- Kramer MS, et al. Effects of prolonged and exclusive breastfeeding on child behavior and maternal adjustment: evidence from a large, randomized trial. Pediatrics 2008; 121:e435-40.
- Bohlen JG, et al. Heart rate, rate pressure product, and oxygen uptake during four sexual activities. Arch Intern Med 1984; 144:1745-8.