The "obesity paradox" — seen in dozens of studies of weight — shows that being a little overweight is not necessarily a bad thing, and could prolong life in some ways, or at least not shorten it.
One study by researchers at the National Center for Health Statistics at the U.S. Centers for Disease Control and Prevention in Atlanta, Georgia, reported in 2013 that being a little overweight was optimal for reducing one's risk of dying. It analyzed data on 2.9 million people in 97 studies.
Researchers found that while moderate to severe obesity was associated with a significantly increased risk of death, mildly obese people had a 5 percent lower mortality risk than normal weight subjects. Slightly overweight people, the study found, had the greatest survival advantage — they had a 6 percent lower risk of death compared to people in a normal weight range.
But a new study by Andrew Stokes and colleagues, published in the journal Annals of Internal Medicine, contradicts the paradox.
Stokes is a professor in the Department of Global Health at Boston University's School of Public Health and Development, and senior author of the new study.
Critics like Stokes said prior studies concluding there is an obesity paradox are flawed because they don't take into account a person's weight history.
Stokes said most of the studies that have been done on weight and its relationship to mortality take a single weight measurement, or snapshot in time, while also recording measurements such as glucose and cholesterol levels, as well as blood pressure — which might be normal. Then, during a follow-up period, the mortality rates of heavier individuals are compared to the number of deaths among people within normal weight ranges.
Stokes said those studies don't take into account the fact that some of the leaner individuals, used for comparison purposes, were battling diseases that ultimately led to their deaths during follow-up.
A better approach, said Stokes, is what he and his colleagues did in their study. They followed the health of 225,000 participants over a 16-year period, in three prospective studies, and then examined deaths that occurred over the next dozen years.
Investigators found that people who were defined as obese or overweight according to a formula called the body mass index were at elevated risk for all causes of death, including cardiovascular disease, cancer and respiratory illness.
The highest risk of death, said Stokes, was seen among participants in the normal range who had significant drops in weight, reflecting unintentional weight loss due to illness.
"People on the pathway to dying often develop illnesses that make them lose weight. So, some people in the normal weight range are there not because they are in good health, but because they've developed a disease such as heart disease or cancer," Stokes said.
The key to good health, according to the authors of the new study, is losing weight if one is carrying around extra kilos, then maintaining the lower weight over a long period of time.
Stokes said he's worried that studies that show being overweight might be good for your health have a message that trickles down to the public at large.
Stokes noted that more than one-quarter of the world's population is overweight, a problem that's emerging in low- and middle-income countries due to the availability of sugary drinks and processed food.
These foods can lead to chronic health problems, such as diabetes. So, said Stokes, people should not falsely believe that being overweight due to these indulgences is a prescription for good health in the long run.
"It's a message that could potentially create apathy toward weight loss and maintaining a healthy weight," Stokes said. "So, one implication of this study is that even a bit of excess weight can be harmful, and it's really important to prevent weight gain and to maintain a stable healthy weight across the life course."
