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The Big, Fat, Truth: public health, weight and mortality
has a thought-provoking news feature: The big fat truth
More and more studies show that being overweight does not always shorten life — but some public-health researchers would rather not talk about them.
Some interesting quotations:
The report, a meta-analysis of 97 studies including 2.88 million people, had been released on 2 January in the Journal of the American Medical Association (JAMA)1. A team led by Katherine Flegal, an epidemiologist at the National Center for Health Statistics in Hyattsville, Maryland, reported that people deemed 'overweight' by international standards were 6% less likely to die than were those of 'normal' weight over the same time period.
The result seemed to counter decades of advice to avoid even modest weight gain, provoking coverage in most major news outlets — and a hostile backlash from some public-health experts. ...
But many researchers accept Flegal's results and see them as just the latest report illustrating what is known as the obesity paradox. Being overweight increases a person's risk of diabetes, heart disease, cancer and many other chronic illnesses. But these studies suggest that for some people — particularly those who are middle-aged or older, or already sick — a bit of extra weight is not particularly harmful, and may even be helpful. (Being so overweight as to be classed obese, however, is almost always associated with poor health outcomes.)
The reporter describes some of the opposition and the counter-arguments. The article discusses other factors that might be relevant and provides a reasonable, sideways overview of why BMI, by itself, is unhelpfully crude.
Metabolic reserves could also be important as people age. “Survival is a balance of risks,” says Stefan Anker, a cardiology researcher at Charité Medical University in Berlin. “If you are young and healthy, then obesity, which causes problems in 15 or 20 years, is relevant,” he says. With age, though, the balance may tip in favour of extra weight.
Genetic and metabolic factors may also be at play. Last year, Mercedes Carnethon, a preventive-medicine researcher at Northwestern University in Chicago, Illinois, reported that adults who develop type 2 diabetes while they are of normal weight are twice as likely to die over a given period as those who are overweight or obese11. Carnethon says that the trend is probably driven by a subset of people who are thin yet 'metabolically obese': they have high levels of insulin and triglycerides in their blood, which puts them at a higher risk for developing diabetes and heart disease.
All this suggests that BMI is a crude measure for evaluating the health of individuals. Some researchers contend that what really matters is the distribution of fat tissue on the body, with excess abdominal fat being most dangerous; others say that cardiovascular fitness predicts mortality regardless of BMI or abdominal fat. ...
If the obesity-paradox studies are correct, the issue then becomes how to convey their nuances. A lot of excess weight, in the form of obesity, is clearly bad for health, and most young people are better off keeping trim. But that may change as they age and develop illnesses.