Monday, November 18, 2013

7 myths about obesity

Obesity - the medical condition where excess fat tissue accumulates in the body - is the leading preventable cause of death worldwide. Excess body fat contributes to a number of medical conditions, including diabetes, high blood pressure, arteriosclerosis and sleep apnea. Governments search for solutions to this huge public health problem, while the media inundate us with advice about diets, calorie counting and exercise. Unfortunately, a number of beliefs about obesity remain popular despite scientific evidence to the contrary. 

In an article recently published in the New England Journal of Medicine, Casazza et al. describe seven myths about obesity - beliefs that persist and are perpetuated by the media even though research shows otherwise.

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

Fact: Predictions suggesting that large changes in weight will accumulate indefinitely in response to small sustained lifestyle modifications rely on the half-century-old 3500-kcal rule, which equates a weight alteration of 1 lb (0.45 kg) to a 3500-kcal cumulative difference in consumed energy. However, recent studies have shown that individual variability affects changes in body composition in response to changes in energy intake and expenditure, and in reality, the changes in weight that do occur across extended periods are substantially smaller than the 3500-kcal rule would predict. For example, this rule suggests that a person who increases daily energy expenditure by 100 kcal by walking 1 mile (1.6 km) per day will lose more than 50 lb (22.7 kg) over a period of 5 years, but the true weight loss is only about 10 lb (4.5 kg), assuming no compensatory increase in caloric intake.

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

Fact: Although this is a reasonable hypothesis, empirical data indicate no consistent negative association between ambitious goals and program completion or weight loss. Indeed, several studies have shown that more ambitious goals regarding weight loss are sometimes associated with better outcomes.

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

Fact: Within weight loss trials, more rapid and greater initial weight loss has been associated with lower body weight at the end of long-term follow-up. Although it is not clear why some obese persons have a greater initial weight loss than others do, a recommendation to lose weight more slowly might interfere with the ultimate success of weight loss efforts. 

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

Fact: Readiness does not predict the magnitude of weight loss or treatment adherence among persons who sign up for behavioral programs or who undergo obesity surgery. The explanation may be simple - people voluntarily choosing to enter weight loss programs are, by definition, at least minimally ready to engage in the behaviors required to lose weight. 

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

Fact: Physical education, as typically provided, has not been shown to reduce or prevent obesity. Two meta-analyses showed that even specialized school-based programs that promoted physical activity were ineffective in reducing the incidence or prevalence of obesity. 

Myth #6 Breastfeeding is protective against obesity.

Fact: Studies with good controls for confounding (e.g., studies including within-family sibling analyses) and a randomized, controlled trial involving more than 13,000 children who were followed for more than 6 years provided no compelling evidence of an effect of breastfeeding on obesity. However, breastfeeding does have other important potential benefits for the infant and mother and should be encouraged.

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

Fact: A man weighing 154 lb (70 kg) expends approximately 3.5 kcal per minute (210 kcal per hour) during a stimulation and orgasm session. This level of expenditure is similar to that achieved by walking at a moderate pace. Given that the average bout of sexual activity lasts about 6 minutes, a man in his early-to-mid-30s might expend approximately 21 kcal during sexual intercourse. Of course, he would have spent roughly one third that amount of energy just watching television.  

An obese girl, painted by Juan Carreno de Miranda in 1680. Image from: Wikipedia.

My comment to all this is that, although research shows that genetic and psychosocial factors can contribute to overeating and fat accumulation, it does seem that a wide availability of energy-dense foods and sweetened drinks, a sedentary lifestyle and, perhaps, a wired-in tendency to eat more than we need are the main culprits in the obesity epidemic. Unfortunately, the simple answer "eat less and exercise more" is often impossible to implement. When you're an overworked adult who, since childhood, is used to comfort eating, it's much easier to munch on a cookie (or a bag of cookies) than to spend an hour jogging, and that's assuming that you're fit enough to go jogging in the first place. Sugary and fatty foods cause the brain to release euphoria-inducing chemicals and can be addictive just like drugs (and yes, there are studies to prove this). Since obesity is such a drain on taxpayers' resources, I sometimes wonder whether, in 15 or 20 years, we will all find ourselves on food stamps restricting us to a 2000-calories-a-day, five-portions-of-vegetables diet, with sweets only available in special stores, to people of normal weight. And even though I'm one of the lucky folks who have never carried extra pounds (I have a really delicate stomach - can't eat fried starchy foods or burgers, and I'm not a fan of white bread or sweets), I seriously hope that this Orwellian vision will not come to fruit.

Casazza K et al. (2013) Myths, Presumptions, and Facts about Obesity. N Engl J Med. 368(5): 446–454. doi: 10.1056/NEJMsa1208051


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