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Analysis: Health pros must not spread obesity myths

Thursday January 31, 2013
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Myths about obesity lead to poor policy decisions, inaccurate public health recommendations and wasted resources, according to an analysis by an international team of researchers.

David Allison, PhD, associate dean for science in the School of Public Health at the University of Alabama at Birmingham, and fellow researchers analyzed articles published in the scientific and popular press to separate myths from evidence-supported facts. The authors defined myths as beliefs about obesity, many of which are fervently held despite evidence to the contrary.

"False and scientifically unsupported beliefs about obesity are pervasive," Allison said in a news release. "As health professionals, we should hold ourselves to high standards so that public health statements are based on rigorous science. In instances where the science doesn’t exist, we should conduct rigorous studies to find the answers."

The seven myths, published in the Jan. 31 issue of the New England Journal of Medicine, are:

• Myth 1: Small, sustained changes in number of calories taken in or burned will accumulate to produce large weight changes over the long term.

Fact: Small changes in calorie intake or expenditure do not accumulate indefinitely. Changes in body mass eventually cancel out the change in calorie intake or burning.

• Myth 2: Setting realistic goals in obesity treatment is important. Otherwise patients become frustrated and lose less weight.

Fact: Some data suggest people do better with more ambitious goals.

• Myth 3: Gradually losing weight is better than quickly losing pounds. Quick weight loss is more likely to be regained.

Fact: People who lose more weight rapidly are more likely to weigh less, even after several years.

• Myth 4: Patients who feel "ready" to lose weight are more likely to make the required lifestyle changes. Healthcare professionals therefore need to measure each patient’s diet readiness.

Fact: Among those who seek weight-loss treatment, evidence suggests that assessing readiness neither predicts weight loss nor helps to make it happen.

• Myth 5: Physical education classes play an important role in reducing and preventing childhood obesity.

Fact: Physical education, as typically provided, does not appear to counter obesity.

• Myth 6: Breast-feeding protects the breast-fed offspring against future obesity.

Fact: Breast-feeding has many benefits for mother and child, but the data do not show that it protects against obesity.

• Myth 7: One episode of sex can burn up to 300 Kcals per person.

Fact: It may be closer to 5% of that on average, and not much more than sitting on the couch.

The authors also defined six "presumptions" — beliefs held to be true even though more studies are needed before conclusions can be drawn. For instance, some advocates have presented as fact the idea that regularly eating versus skipping breakfast contributes to weight loss, but the few studies that have been done have found no effect. The same goes for the idea that eating vegetables in itself brings about weight loss, or that snacking packs on the pounds. According to Allison and colleagues, these hypotheses have not been shown to be true, and some data suggest they may be false.

The researchers also identified research-proven weight-loss facts. For example, weight-loss programs for overweight children that involve parents and take place in the child’s home achieve better results than programs that take place solely in schools or other settings. Also, many studies show that while genetic factors play a large role in obesity, "heritability is not destiny." Realistic changes to lifestyle and environment can, on average, bring about as much weight loss as treatment with the most effective weight-loss drugs on the market.

Although difficult for many to sustain over the long term, eating sufficiently fewer calories effectively reduces weight. Exercise is useful, but only when frequent and intense enough to use up more energy than taken in, and one must not compensate for that exercise by increasing food intake or decreasing movement at other times.

Although the scientific community agrees that randomized, controlled trials provide the strongest evidence of a causal relationship, the obesity epidemic has prompted officials to take action before all the facts are in, or when a long-term randomized trial was neither practical nor ethical.

Allison and his colleagues argue that randomized trials are possible even in scenarios where once thought impractical. The 2011 NEJM study of the relationships between neighborhood environment and obesity is an example, and underscores the opportunity for wider use of more rigorous studies to test hypothesized risk factors, treatments or prevention strategies.

The study abstract is available at www.nejm.org/doi/full/10.1056/NEJMsa1208051.


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