Last week, the UK health secretary declared that we are in a grip of an obesity epidemic, but does the evidence stack up? Researchers in this week's BMJ debate the issue.
Claims about an obesity epidemic often exceed the scientific evidence and mistakenly suggest an unjustified degree of certainty, argue Patrick Basham and John Luik.
For example, the average population weight gain in the United States in the past 42 years is 10.9kg or 0.26kg a year. Yet, between 1999-2000 and 2001-2002, there were no significant changes in the prevalence of overweight or obesity among US adults or in the prevalence of overweight among children.
Furthermore, they say, the categories of normal, overweight, and obese is entirely arbitrary and at odds with the underlying evidence about the association between body mass index and mortality.
For example, the study on which the bands for overweight and obesity in the US are based found that the death risks for men with a body mass index of 19-21 were the same as those for men who were overweight and obese (29-31). Other studies have shown negligible differences between body mass index and death rates.
The association of overweight and obesity with higher risks of disease is equally unclear, they write. And, despite supposedly abnormal levels of overweight and obesity, life expectancy continues to increase.
They suggest that some public health professionals may have deliberately exaggerated the risks of overweight and obesity, and our capacity to prevent or treat them on a population wide basis, in the interests of health. They warn that this has unwelcome implications for science policy and for evidence based medicine.
But Robert Jeffery and Nancy Sherwood argue that a large body of scientific evidence shows that obesity is a major global health problem.