Mortality Rates Decreased for Individuals at Lowest Obesity Levels

An interesting study reported in the The Journal of American Medical Association last week found that people whose body mass index (B.M.I.), a ratio of height to weight, ranked them as overweight had less risk of dying than people of normal weight. In the detailed review of over 100 previously published research papers connecting body weight and mortality risk among 2.88 million study participants living around the world researchers at the National Center for Health Statistics, Centers for Disease Control and Prevention, found that while obese people had a greater mortality risk over all, those at the lowest obesity level (B.M.I. of 30 to 34.9) were not more likely to die than normal-weight people.

The researchers found that the summary hazard ratios indicated a 6 percent lower risk of death for overweight; a 18 percent higher risk of death for obesity (at all grades); a 5 percent lower risk of death for grade 1 obesity; and a 29 percent increased risk of death for grades 2 and 3 obesity. It was also noted that the finding that grade 1 obesity was not associated with higher mortality suggested that the excess mortality in obesity may predominantly be due to elevated mortality at higher BMI levels.

It has been suggested that overweight and obese people get better medical care, either because they show symptoms of disease earlier or because they’re screened more regularly for chronic diseases stemming from weight levels, such as diabetes or heart problems. The 6 percent lower death risk advantage held among both men and women, and did not appear to vary by age, smoking status, or region of the world. The study looked only at how long people lived, however, and not how healthy they were whey the died, or how they rated their quality of life.

Instead of viewing the study as a license to overeat, health experts have noted that the study suggests that B.M.I. should not be the only indicator of healthy weight. Additionally, some experts also said the data suggested that the definition of normal B.M.I., currently 18.5 to 24.9, should be revised, excluding its lowest weights, which might be too thin.

Today, roughly 33 percent of U.S. adults are clinically overweight, according to WHO standards, and an additional 36 percent are obese. Using those standards, the average American is not considered clinically at normal weight, but overweight. Yet, at least among this group of Americans, the overweight people in the study who tended to live longest may not be fatter than most people but may actually be of average weight.